2021.09.12 | Glenn Diekmann: Imaging Through the Light Dome

zero hi everybody welcome back to the astro imaging channel on this sunday night the first full night of nfl action we have something else for you today it's not working if you've been watching stop alex please it's not working okay eric it's not working from what you can see the video's not coming through no it's black screen but the audio is coming through that's weird uh tim do you want me to it's on now i got it okay hi everybody we're back hi everybody welcome back to the astro imaging channel it's the first sunday of nfl football the national football league is back so you may be distracted but this is more important this is your sunday night astro imaging club meeting the astro imaging channel and we're so glad to have you back uh we've got some things happening for you and i do need to tell you about those things um and so i'm going to present my screen and click over to the astro imaging channel and oh i'm not there yet i want to go over here we've got two projects going for you nebulae the beauty of dust and you click on tack shows check shots up here to get into that and then eric coles has his m33 processing data out there so uh if you go to tech workshop you get into that you can go get all of this data and we really want you to go do that go get the data it's good clean data like all of eric's data and it's so much fun to process clean data so um you link to the data files here download them and then when you're finished click here to submit the file and we'll put the show together sometime uh you got till october 17th so it's a little more than a month to do that and then um and then we'll have a show sometime in november or something like that to show everything that's gone on uh and we also have um we also have if you go over to the tech shots you can submit your images of nebulae and um same kind of thing and we'll make a movie out of it arnold's going to be hard at work at that so um we hope you enjoy that and uh i also like to go during this portion of the show just uh real briefly go through the calendar a little bit get you excited about some of the upcoming shows and tonight glenn's going to tell us about imaging through the light dome which will be pretty cool and then queef the lazy geek is going to be here next week he's put out a lot of really good uh videos and a lot of people really like them queef are you still here with us tonight can you um i am here i am here what are you going to talk about next week so next week we're going to talk about um imaging in difficult conditions which does include something similar to glenn uh imaging through a light dome but some other other stuff other tips and tricks and probably a lazy lazier way to go through things since i do like to be lazy but yeah i'll i'll make sure that we don't uh cover too much of the same ground yeah just what i need more help being lazy and then i go back to sharing again and one of the things i should tell you is that is that just by a quirk of of the way things are linda is coming in on october 3rd and she's going to be quantifying the effect of dark skies which is somewhat related to what glenn is talking about this week we've talked about next week and then when i was visiting my cousin back in back last summer i found a gian lorenzo ferratti uh he was in an article in the chicago sun times and he's talking about imaging from the city so he'll be here november 7th so we've got four topics talking about it and when we were talking in the warm-up before the show we said wow that's a lot huh and as glenn pointed out yeah that's because we all need to know about this kind of stuff but we've also got one of the one of the people that keeps phd running uh coming in next week peggy walker will be here not next week on october 10th peggy walker will be telling us about tactile astronomy resources for the blind and disabled and how to use our images to help people that may be a little bit handicapped to enjoy the night sky but you can see that while we're good until all november or something actually i think we're good until december um we start having problems after that okay we we don't have any more uh dates after that so you need to hit the presenters the the contact link here and uh tell us that you'd like to do a show for us and tell us what you'd like to do it about and we'll talk to you a little bit about it and maybe we'll put you on the show and you can share your knowledge remember you're an astro imager that means you're pretty smart and you can do things that the average guy can't do the average girl can't do you're because you're smart and you know how to handle technology and stuff like that you are capable of putting on a show if you've done something in astro imaging that you'd like to tell other people about or you see people you know struggling on something you need to pitch in on the astro imaging channel and do your thing okay so contact us and get into it now i asked glenn to be here because i know glenn puts out really good images i see him on occasion and i'm going to ask glenn to go ahead and take over while the rest of you guys all go out there on the astro imaging channel on youtube and ask your questions of glenn as we go along glenn you ready i'm ready okay take over all right okay um you see my screen i'm seeing it it's not presenting yet here we go play or whatever you do yep there you go now now it looks like you're presenting okay well uh thank you very very much for uh for letting me be here i've been watching the astro imaging channel for years and i've learned so much from it and uh it's an honor to to finally be presenting on it my name is glenn diekmann and i'm going to be telling you about imaging through the light dome or doing astrophotography from a light polluted place or a light polluted sky here's the outline i'll start by giving a little bit of information about myself and uh the uh the location where i do most of my imaging from i'll tell you about the problem of light pollution where it is why it is and then i'll get into the the the heart of the talk which is the strategies to mitigate the effects of light pollution you know things that i've discovered or learned along the way to to make it just a little bit easier i will be uh presenting examples from my own work along the way and uh and then at the end we'll we'll wrap things up and hopefully tie it together feel free to to stop me at any point when there are questions okay and we'll also have time for questions at the end all right so a little bit about me uh my background is in medicine i'm not an engineer or a physicist and i mentioned that only to say that i didn't intend this talk to be a super technical one i um tried to make it uh accessible and um and practical so that's been my approach i live in the los angeles area and los angeles is a pretty big city with a lot of light pollution i have always been enjoying the night sky uh always looking up and uh wondering what was out there and then finally uh when i was um in in 2015 i guess about six years ago i found a guy who was selling a celestron 8se in my neighborhood and i bought that thing and i set it up on my lawn and uh the um it's a go-to mount and it has a an alignment routine that asks you to point the scope at three bright objects many of you are probably familiar with this so it didn't ask for stars or i didn't even have to know what the objects were just three bright objects and lo and behold that's what i saw in my eyepiece and my mind was completely blown i wouldn't i i was i guess expecting to see a star i wasn't expecting to see a planet let alone a planet with rings and it was just the most amazing thing i'd ever seen and uh in my mind this this is how it looked and it left a lasting impression on me i uh i've been into astronomy ever since and i love visual i love imaging but uh because of light pollution in my area i tend to do a lot more um i tend to do a lot more of the imaging um so i belong to the same astronomy club that alex mcconaughey uh belongs to and it's called the riverside astronomical society and it's a great club and they have a wonderful dark site called gmars and it's wonderful and i enjoy myself every single time that i go there unfortunately because of work and family commitments i just never seem to be able to get out there more than a couple times a year or so right now so as a result i do most of my imaging from my home from my backyard so i think it's important to show you where i image from so that you can understand the the context of my experience and and the things that i'm telling you all right so this is the side of my backyard looking to the north and my roof line is over here on the left my neighbor's roof is on the right and there's a great big hedge on the north end of it and and that gives me this sort of strip of the sky looking northward and looking southward it's kind of the same thing i've got uh it's reversed here but uh but you know roofline roofline and um you know and that's it so i call this my my alleyway view of the sky or my bowling alley view of the sky it's a narrow strip but you know it could be worse i can see things pretty far to the north i can see objects pretty far to the south and i have a pretty good view through the meridian which is what uh you know matters for imaging anyway so i'm not complaining however when i look to the south um i really have problems with light pollution and the reason for that is i live in a sprawling metropolis that's what los angeles is and i've circled the city there and that's me the blue dot about 30 miles away or so but everything around it is just densely packed um a high density population and what i'm showing you here probably represents 10 or 12 million people so it's congested and uh it is bright the night sky is very bright and what i'll draw your attention to here is um i'm on the edge of a mountain range and that does give me some reprieve from the light pollution i have a somewhat darker sky looking northward but anything to the you know to the west and to the east and the south i'm i'm dealing with all this and i suspect that many of you are in a similar situation here's the street i live on and uh the first thing you notice is uh the bright street lights bright unshielded street lights uh shining you know not just the ground on the ground but into the sky laterally there's a lot of landscape lighting and the sky is just a pale featureless thing with you know some stars you can probably make out but not a whole lot and it's pretty bright near the horizon there and uh this would be looking kind of west by southwest and that's los angeles uh sort of in that direction so um and and here is uh so this is the same uh this is i showed you where my scope was on the side yard and this is actually during an imaging session this is about midnight and what you notice here it's a little bit underexposed but what you notice here is just how gray and bright the sky is in case you can't see my telescope uh there it is and you can probably make out the uh bright led of my mini pc sitting on top of the scope but that's a really bright gray featureless sky and just for reference here's jupiter jupiter is one of the brightest objects in the night sky and it shows up as this faint little dot um you know in from from my backyard so as i said that's what i'm dealing with um i i suspect that many of you are dealing with the same sort of thing so what's the problem light pollution is the problem and it is caused by too much outdoor lighting and the wrong kind of outdoor lighting what do i mean by the wrong kind well i just showed you the wrong kind the um lights that are not shielded they don't just illuminate the thing they're supposed to illuminate but rather they uh send a lot of light in in directions that uh that don't help lighting the the intended source so straight into the sky uh to the side where it contributes to glare um that sort of thing and when you take a lot of people and you put them in an urban urban setting and everyone has outdoor lighting this is what you get and the picture to the right shows uh kind of the worst case scenario of that about well i would say 80 plus of the world's population lives in urban uh areas or suburban areas and as a result uh about 80 percent of the population cannot see the milky way at night and i couldn't either i mean i still can't but uh i didn't see the milky way uh until my wife and i went to hawaii 12 years ago or so that was my first time seeing it that's a shame as it's breathtaking but but the sad reality is that most people can't here's a um here's an interesting picture that i found on the international dark sky association website and apparently there was a huge power outage in 2003 that affected 50 million people and the lights across multiple states just went out and this picture on the left was taken before the power outage and the one on the right is after and i don't know about you but i would never have guessed that on the picture on the left that the milky way was stretching just above uh that house so this to me really drives home how much uh the light pollution is depriving us of our view of the night sky uh this just shows you know urban centers are bright there's um in every you know every major country uh they've got big cities and big cities have lots of lights and so this is kind of a nighttime satellite view uh demonstrating that this is my neck of the woods again this is essentially the same map that i showed you earlier of where i live and i'm behind the target here and it's bright there's lights in every direction except as i said to the north i get a little bit of a reprieve because of the mountain range that's behind me uh alex mcconaughey is out here somewhere so he's got it pretty bright as well all right uh john bortle is an astronomer and an astronomy journalist who proposed a scale for raiding the darkness of a sky and it goes from one for an excellent pristine dark side all the way to nine which is basically your inner city uh sky that's almost white and completely featureless and then there's you know a variation in between my sky's about a seven so take that uh everything that i'm telling you is um you know from the perspective of someone who's in a sort of a bordeal seven sky all right now i want to be very clear that there is no substitute for a dark sky the pictures that i get at g mars or other dark places are they just always seem to be a little bit better than what i can achieve from my backyard say for example you're at uh you take a one-hour exposure at a nice dark place with sky brightness of say 21.8 magnitudes per arc second that's a pretty dark uh dark sky if you go to a place that's only one magnitude brighter you would need two and a half times the exposure to get the equivalent image or the equivalent image quality if you go someplace two magnitudes brighter you would need 6.3 times and i'm right in here at the 18.8 to 19 range so i'm somewhere in between 15 almost 16 times brighter and all the way to 40 times brighter for a 4 magnitude difference and you know even when i say equivalent image quality i mean it's never going to be quite the same um but this just drives home what a what a big difference having a dark sky can make so those of you who have a dark sky i i hope you appreciate it um all right so that brings us to the strategies how do we deal with this problem um first i'm going to tell you about signal to noise ratio because everything sort of comes down boils down to optimizing your signal to noise ratio so snr and signal to noise ratio i'll be using those in interchangeably for the purpose of this talk signal is simply useful information and uh specifically it is the light that is coming from your target whatever you're taking a picture of that's what you want to put on your camera sensor that's the signal unfortunately that always comes with noise and noise is uncertainty in that signal and it manifests as a graininess in the in the pictures that we take so uh signal and noise are inextricably linked and when you add signal you will always add noise however there is an important relationship to understand between the two that uh that we can exploit for the purpose of astrophotography the signal adds in a linear fashion but the noise adds with the square root of the signal and what that means is as you collect data and you you add to your data your signal is going to build and build and build in a more or less linear fashion but your noise although it will add it will add at a slower rate and therefore the difference between the signal and the noise will increase and you'll get an increased signal-to-noise ratio it's um it's a pretty deep topic i discovered in researching for this talk and uh there are it's pretty math heavy theory every heavy and i don't intend to get into that but i refer you to the excellent talks by doctors craig stark robin glover and others if you're interested this this diagram just depicts what i was trying to explain in the previous slide the signal will build linearly but the noise although it builds it builds more slowly so you get an increase in the ratio between the two all right so the goal of um the goal of dealing with light pollution in fact it's true for all of astrophotography is you want to optimize your signal-to-noise ratio and i like to distill things down to their essence whenever i can because it helps me understand them better so the uh the way i think about optimizing signal-to-noise ratio when i take pictures is i want to number one uh collect my photons efficiently i want to collect lots of photons and then i want to collect photons that i'm interested in so by that i mean the photons coming from the target and not necessarily the the photons coming from the sky okay so i'm going to tell you about collecting photons efficiently first all right so there's two ways to do this uh there's probably others but these are the two that i've identified uh you can do it better with a fast telescope and with a sensitive camera okay so i'll start with a fast telescope what do i mean by that well to uh to to understand you need to first understand what um excuse me um you need to understand focal ratio and focal ratio is the relationship between focal length and aperture of the telescope and it's expressed as number and f number like f 2.8 f6 you've probably seen such numbers if you're doing terrestrial photographies it's the same thing and the importance of it is it determines how much light from the telescope falls on each pixel of your sensor okay and for the purpose of the talk i'm going to be calling things less than uh telescopes with an f ratio less than f5 to be relatively fast and those greater than f5 to be relatively slow and in deep sky imaging we tend to use at most a ratio of f10 f11 maybe and it's usually a lot closer to f5 and lower all right this uh this diagram i think really clarifies the idea so on the left we have an f10 optic and that's you know a relationship so the focal length divided by the aperture in this case is 10. and what you can see and there's the sensor at the bottom and what you can see is that the uh the light entering the funnel if you think of it as a funnel shape the light entering um it doesn't really uh it doesn't really collect much of the light because the funnel is quite narrow now by doubling the aperture we produce an f5 optic and that really broadens the opening of the funnel and it's able to collect a lot more light and focus that light on the sensor in astrophotography we don't do that so much we don't routinely increase the aperture of our telescope that would mean basically changing telescopes but what we do commonly do is we change the focal length of our telescopes with focal reducers and um that ends up doing the same thing you can take an f10 and turn it into an f 6.3 or something like that by shortening the focal length but it wasn't as intuitive in the diagram so i went with this one but astrophotographers tend to do it the other way all right so a lower focal ratio is good it's a good thing and as i said it concentrates more light onto each one of your pixels and it results in shorter exposure times and it will produce a wider field of view and a decreased object size on your sensor and that may or may not be a good thing depending on what you're trying to achieve and it will give you a better signal-to-noise ratio okay so that was how to collect photons with a faster telescope now let's talk about a sensitive camera first we need to understand quantum efficiency all right so the light enters your telescope and um you know it goes through the optics and then it hits the sensor some percentage of those photons will be converted to electrons which becomes signal that the camera can use to produce an image and a quantum efficiency can be thought of simply as electrical sensitivity to light and it's expressed as a percentage of photons converted to electrons okay on that sensor this is a um a quantum efficiency curve for a variety of sensors um and what you see here along the bottom x-axis is the wavelength of light and then the quantum efficiency zero to 100 on the y-axis and every one of these sensors has i want you to notice um a peak uh quantum efficiency okay this is hovering right around 78 80 for the one in green that's the sony 674 ccd uh and then there are other ones that are much lower right so a peak uh efficiency of 40 45 so and it also uh falls off in the very short wavelengths and in the very long wavelengths okay here's another uh another view and this is a mixture of uh kodak or on semi uh sensors as well as some sony sensors and again you see the the you know the variation with the peak but there's also these lines and uh i want you to pay attention to these for a moment so this is o3 that's ha and this is s2 and those are uh specific wavelengths that are very important to astrophotographers and to astronomers in general all right and a given sensor might be very sensitive in one but less sensitive in the other and if we compare uh a couple of them like this is the the 8300 that's a very i mean it's ubiquitous it's been out for for years and i i have one of these as well but its quantum efficiency in the s2 wavelength is only 40 percent and then 44 percent for ha uh o3 is only 48. compare that to the sony sensor and you've got uh you know 61 65 76 so judging uh based on that alone it's a much more efficient sensor now uh sensor efficiency is very very uh important and i've found that it helps me to collect photons more efficiently for sure but it is far from the only consideration when setting when choosing a camera you have to look at image scale and sensor size pixel size uh full weld depth and read noise dynamic range and other things so um obviously there's a lot more to it than that you don't just want to pick the most sensitive camera but it's just one thing that you can look at if you're trying to uh to be more efficient with your photon collection all right now let's talk about collecting lots of photons so astrophotographers don't just take a single picture of an object when it's uh when it's up in the sky they take many many pictures sometimes over multiple nights until they have hours and hours worth of pictures and then through [Music] a process called stacking they they integrate these pictures into one master image and and stacking uh takes this information from the individual images and makes a new image with a much higher in some cases signal-to-noise ratio okay so stacking will give you a higher signal-to-noise ratio and along with that you get noise reduction okay that goes hand-in-hand with that and the relationship again like i showed you earlier it's the square root of the number of frames stacked so sound familiar and this is how it looks let's say you have two frames instead of one you're going to reduce your noise by 1.4 x 4 frames gives you a 2x reduction basically cutting your noise in half and so forth you know 25 frames gives you a five-fold reduction in the noise and then finally 400 frames giving you a 20-fold reduction in the amount of noise and it's a very powerful effect so i'll show that to you now here's an example this was uh this is again taken from my backyard this is andromeda the andromeda galaxy and this is a single frame with my 8300 sensor 60 seconds and this is the kind of thing that doesn't come through very well on youtube so i apologize in advance but what i'm seeing here is that the background has a lot of graininess to it and uh you know you can tell it's a galaxy and all that but it's you know not very bright the details are faint okay bringing it to four frames and what you see is the background really becomes smoother and the object itself becomes much brighter so there's one frame four frames one frame four frames going to 16 frames halves the noise again so four frames 16 frames i mean that's a big that's a pretty big jump i think and now we're starting to see nebulosity all the way out to the edge of the of the galaxy and the background is looking much much smoother all right and here's 200 frames that's about a 14-fold decrease in the noise okay and i know that's hard for you to see so maybe you can see it a little bit better if i do it if i show it to you this way so up here it's grainy and uh you can see the this is sort of the upper left uh edge of the galaxy that i'm showing you so this is you know pretty dark kind of grainy a little bit brighter down here going to four frames it's a little smoother you know and uh and getting a little bit brighter here but by 16 frames i'm starting to see things up here that i did not see over here and that's what i meant when i said earlier that that noise is uncertainty in the signal because you can't tell if you're looking at what what these grains represent is there something really behind there or is it just um you know bad information or noise by the time you get to here you can see that yes in fact there is nebulosity right here i would never have guessed that from this first one and then finally by the time you get to 200 frames what i'm looking at here essentially shows no noise anymore and not only can i see the nebulosity but i can start to see some nice uh you know dusty details in there as well so you know stacking gives you this amazing improvement in signal-to-noise ratio your noise goes down it's in my opinion it's the best form of noise reduction all right now let's talk about collecting only the photons that you are interested in and by that i mean wouldn't it be nice if you could collect only you know put on your sensor only the light leaving your target and none of the light that's coming at you from the sky the sky glow in other words um so that's that's what we're going to talk about next okay first we need to talk about uh just just real quickly about um how this works for certain objects and i want to be clear this works for certain objects and not for other objects all right but imagine that you have a bright star uh with uh that's that's in a cloud of gas or next to a cloud of gas and the bright stars really has a lot of stellar wind and radiation coming out of it and uh it some of that radiation hits the gas cloud and it hits the the atoms or the molecules of the gas cloud and it will excite some of the electrons in the um in that gas cloud and those electron electrons will go up to a higher energy state all right and then they will relatively quickly drop back down again and when they do that they produce or they emit a photon and the reason that's important is when you drop from one energy level to another energy level it's always the same energy value and the wavelength of light that's emitted is always the same and that's that's called emitting a photon and that's why we call these types of nebulas emission nebulas right now looking at the spectrum of hydrogen so you've got your full your full spectrum of light up top but i want you to focus down here there's only four lines and these are the very very tight specific wavelengths that hydrogen will emit photons at so imagine if you had a filter that could let just this through and block everything else uh that would seem like magic and in some cases it works almost like that all right now i need to tell you about broadband versus narrow band uh images so the the trick that i just showed you or the concept that i just showed you applies only to certain types of uh of objects and specifically those emission type objects okay broadband objects emit the full spectrum of light and narrow band objects only emit light mainly in those specific emission lines that we talked about broadband objects include stars galaxies reflection nebulae dark nebulae and then on the narrow band side i already told you about emission nebulae but there's also planetary nebulae and it sort of the same principles apply okay these are the narrow van filters that most people use there's one for oxygen one for sulfur and one for hydrogen alpha and there are other specialty ones but these are the the ones that that most people doing narrow band imaging are using and you can see uh off on the right column the wavelength is very specific 500.1 656.3 so they block all other light except a narrow bandpass just around those frequencies okay so what does that mean now i think an example or two is in order uh what i'm going to show you is uh some of the images i've taken or at least some of the data that i've collected from my backyard and i'm going to show you first some rgb data okay and here's the first one i'm going to show you rgb data and then i'm going to show you kind of an equivalent set of narrow band data for the same target same framing everything all right this is rgb 45 minutes per filter and this represents a simple uh histogram stretch in uh in pix insight i didn't do anything to it i didn't reduce gradient nothing else all right okay so here's rgb and there's narrow band uh 45 minutes per uh hs and oh okay i chose a palette that looks a little bit more natural just to make it more directly comparable to the rgb but i think the point uh is made so what i'm seeing here is just a lot more definition sharper edges a lot more dusty detail and even the um even the ugly gradient over here goes away to a large degree you don't see it over here because it's being filtered out so you your your narrow band filters are getting you a lot of mileage here's another example this is fleming's triangle or pickering's triangle uh in cygnus uh in the cygnus loop and it's part of a supernova remnant uh the rgb version is pretty good you know for only 45 minutes i mean i can i can see all the nice red hydrogen i can see the teal blue uh oxygen signal so i mean it's not bad but i mean it's just it's just no comparison to what you get from uh from narrow band so you know rgb to narrow band and to me this is i mean it is almost you know magical and to do this from a light polluted place is just incredible so so that's narrow band filters okay all right so other tips um maximize the amount of time that you spent on target i already told you that as you collect more and more data you get an improved signal to noise ratio but what if you're setting up every night if you set your gear up every night and you have to polar align and you have to you know troubleshoot and all that you're probably not going to get all that much data so my first recommendation or suggestion for you if you can do it is find some way to have a permanent or a semi permanent setup now i don't have a permanent setup i i do something a little different that i'll mention in a moment but if you have an observatory or if you can make yourself an observatory that's amazing you should do that up here would help tremendously or do as i do and just kind of leave your setup out for multiple days at a time and i i leave the one you know this this setup i leave it out for two three weeks at a time sometimes and i just use uh good scope covers these just a telegizmos uh scope cover and i have one for the you know for the ota as well and my stuff does great outside so that lets me image night after night after night on a target and get enough good data that i have something to you know to work with and really turn into a nice picture what goes hand in hand with that is automation and i think that everyone who's interested in doing this kind of thing needs to automate we're very very fortunate to have so many excellent programs these days there's voyager and nina sequence generator pro and maxim dl i mean there's there's really uh an amazing selection of session management software out there um and i have set mine up i i use voyager i've set mine up to be basically one click uh before sunset and my scope wakes up at the right time it does its auto focus routine and it it you know aligns to the target with you know pixel accuracy and um i wake up in the morning and there's there's data on my hard drive that to me is is amazing um furthermore it lets me make a choice what i want to do with my time sometimes i'll sit out there with binoculars and i'll just look at stuff and um and i love doing that other times i'll go on date night with with my wife or i'll watch a movie with my kids so uh it's you know it's it's nice to have that automation capability another tip is image around a new moon the new the moon is the uh the biggest natural light polluter that's that's up in the sky it reflects 12 percent of the sun's light and if you're struggling with light pollution to begin with don't add to it by shooting uh you know around a full moon wait for the new moon or at least you know on either side of the new moon i'll usually start imaging around the last quarter and i'll go all the way through the first quarter and if i have narrow band imaging to do i'll do it when the moon's a little bit brighter and i'll save my rgb imaging for when you know when it's a new moon and there's no moon out at night all right choose targets that make sense for your sky i see so many wonderful uh wonderful pictures people with scopes and chile and other dark places uh and they're just amazing uh amazingly deep and they have so much fantastic dust and and details that i would love to bring out in my own pictures and then i go and i try them and i just can't do it or at least not to the degree that they're doing it and the the simple truth is certain targets really can't be done um from a light polluted place as uh well as they could be done from a darker place so objects that make sense from a dark sky include globular clusters open clusters um bright emission nebulae those are all good choices um dark nebulae the faint stuff probably not and there's even a limit i think to to what you can do with narrow band filters in light pollution too all right and my last tip is to upgrade yourself and what do i mean by that you know uh this is a a challenging hobby and it requires a lot of effort and a lot of learning and uh a lot of practice to to do right and i see from time to time on astr ben or elsewhere uh images that uh that are taken by people who have some really fancy equipment very you know expensive equipment but the images themselves are a little bit lackluster and and that's fine i'm not saying that everyone should have images that are a certain standard and if the person's happy with the quality of image that is absolutely all that matters but my point is you don't necessarily need the fancy equipment to get the nice image and i think of it as learning how to play a musical instrument for example this guitar if you hand a mediocre guitar to someone uh who really plays well they're going to make it sound amazing and conversely if you take a premium guitar and you hand it to someone who doesn't really know how to play it's just not going to be a good result and i think it's the same thing with astro imaging and many other things frankly so practice practice practice learn picks insight learn photoshop i was intimidated by pix insight and i put it off for a long time for for several years and then finally i jumped in and you know what it was something that wasn't all that hard to learn there are some amazing tutorials out there and it's made a huge difference in my processing i mentioned some of these things there are some excellent books there's free online tutorials light vortex astronomy i think is one that i used early on and then there's some subscription video libraries i use adam blocks all the time i've also used warren keller's and when you consider how much we spend on this hobby i mean thousands or tens of thousands or more than that the cost of a subscription is really pretty pretty trivial and i have learned you know so much from um uh you know from from some of these videos i i just consider it to be one of the best investments you can make in your astrophotography all right um hey do we have any questions at this point um am i doing okay yeah no questions uh yet wow everything's that clear huh yeah no we we've had about 80 some 80 plus people watching which is a pretty good night for us okay and uh there's a few comments about the uh light pollution where we live and stuff like that and a few other stories but everybody's just been fascinated with listening to you give your advice there hey um i got a question i got a little question for you yes um you were going through your list of ideal targets immediately after you did narrowband can you tell us about what the effect of narrowband is on some of those targets for instance globular clusters and narrowbands i've just never put them into the same bag so maybe maybe we should maybe you should explain a little bit about that well i think what i meant to say was certain targets are not suitable for narrowband and i wouldn't for example try to shoot a globular cluster or um a galaxy through a narrow band filter because it's just those are broadband objects they're producing light across the whole spectrum and it's just not going to look right if you try to uh to image it through a narrow band filter so yeah sorry if i didn't make that uh clear and the other thing is that you are using monochrome with various filters you're not using one shot color with one of those tripods i totally forgot to mention that yes this is my this is mono camera and uh and filters okay yes you know uh glenn i think it's there's probably one more thing to mention i had to switch mics i hope you can hear me but yes i can hear you it's a fairly easy calculation if you look at say a red filter which will capture all the light from an emission nebula it's about let's say 125 nanometers wide if you have a three nanometer filter that just gets all the emission you're only getting one-fourth of the light pollution but you're getting all of the red and and that's kind of how that works it's not just that it's narrow but it's eliminating everything else everything else you don't get more signal red signal you just get you know 140th of the ex the light pollution that you would normally get even with a red filter yes now that that is an excellent way of saying that too but uh but yes that's absolutely the case well said all right shall i carry on yeah please okay all right so uh wait wait glenn i'm sorry glenn we forgot to tell you in the warm-up that we turn our microphones off when we're um we're not talking and so if you if you say any other questions and like i was fumbling from my mic button anyway uh there was a question it was just eerily quiet that's all yeah uh um there was a question from who was it what's uh um uh renin vander wingard uh how about taking hydrogen alpha with the full moon or at a target that's 45 degrees or more away from the moon have you had any success with that yeah yeah i've done it and uh and i i showed you my view to the south i mean it's uh i've got terrible light pollution out that way and i've taken some low objects i mean with uh a declination of um oh what would it be something that's only like 26 uh degrees over the horizon for example so low i mean more than like a two two air mass kind of a situation and um yeah i use narrow band i mean that's the only way i can shoot to the south uh and get a decent image i really can't do uh rgb when i'm pointing really low in the south it's just the the light pollution is overwhelming okay and you're lucky you've got a national forest to the north i pointed out earlier that is fortunate yes yeah um uh but is it jeff wants to know i know jeff once jeff commented that he wished that they weren't we didn't have broadband led lighting but rather had selected the parts of the spectrum but john ed astra wants to know what's your exposure length how do you optimize exposure length that is a very good question and there's a lot of discussion about that on the forums i will expose to get my background over the reed noise and i do a simple calculation for my camera to kind of figure out what the what the read noise is and uh how much over the bias signal in other words the the zero second exposure signal for my camera would have to be in order to kind of drown out that that noise a little bit um and then i i consider my target if i'm shooting a target that has a relatively few stars i'm inclined or at least not very bright stars i'm inclined to let the exposure maybe go a little bit longer as long as i'm not blowing out stars once you start blowing out stars you start to uh you know you start to clip them and that hurts your star color so for me it's a little bit of a uh maybe do some calculations or just know your equipment uh to to to know where to start your exposure and then i just adjust i do a few you know when i'm starting on a target i'll do a couple of uh trial exposures just to see um you know how they how they look and i've even found that during an imaging run let's say i'm collecting 03 on something and i've got a three-minute exposure set up and it looks like it's kind of borderline maybe a little bit underexposed i'll go to a four minute exposure uh next and so there's always a little bit of trial and error for me but i want to make sure the background is bright enough uh you know the sky you know i'm drowning out my read noise and i want to make sure that i'm not clipping too many stars and beyond that i don't get too fussy about it um the astronomical league has a program called the urban observer and it suggests that you it has targets that you can see from the city and they also have a list of suggestions there as to um uh that you observe after midnight because the stores close down and the traffic's less and there's less light pollution so you've got a better chance of seeing things i don't buy it have you have you ever noticed whether there's a change in exposure values caused by the cycle of life gaming down and people turning off lights there is a little bit uh in my area anyway um i do have a sky quality meter and uh sometimes i'll just check it at the beginning of an imaging session then um a little bit later in the night if i happen to be walking out to check on my rig and you know not always but uh but sometimes it's like a tenth of a point uh lower you know i mean who knows if it makes a difference in the in the final image but um i'm more concerned about total imaging time so i start generally at astronomical night and when my target clears my neighbor's roof and that's when my imaging session starts because i don't have a huge view of the sky i've just got that little narrow alleyway like i said so i'm more concerned about just getting on target as early as i can imaging night after night and then i will weed through my sub frames in pix insight later to pick the quality ones okay uh eric you want to take the questions that have come in while we've been talking lance mann and martin have a couple of questions right i have to click my microphone as well narrowband filters how narrow as it relates to the difference in portal scale not sure what that question is but that's how it reads well i think they're asking you know how narrow narrowband filters are sold as 12 uh uh seven or threes which one is better and how does it relate to your light pollution situation well you know that the narrower the band the more expensive the filter by a significant amount but the narrower the band the higher the ratio of emissions that you see versus the background and the stars so i think they've kind of priced it you know they know the narrower band filter is going to cost more because it gives you a better result so i think my recommendation always is get the narrowest band filter you can afford i glenn have you what what do you what are your uh what's the bandwidth of your filters i use five nanometer and i had three nanometer but then i switched to um faster telescopes with f ratios less than four in some cases and what i found was i was actually clipping part of that um bandwidth and i was getting less signal with my faster scope than um i had with the slower scope so the band pass that each filter gives you um it shifts a little bit depending on the focal ratio of your scope so if you have a longer focal ratio or or a higher focal ratio scope you can use any any uh band pass filter that you want i mean you can use threes no problem but as you get down close you know below four and close to you know two or whatever you have to make sure that you're using a filter that is going to pass the light you think it should pass for a system as fast as yours and they do make some filters that are designed specifically for lower focal ratio scopes so i had threes i found that it was hurting my images and i actually went up to fives so i use five nanometer astrodon filters yeah mark marsha asked about the dual narrowband filters you have any thoughts about that uh for um for color imaging i mean for for one shot color uh a one shot narrowband yes yeah you're talking about the the the double band pass or the triple band pass filters that are out i mean i i'm seeing some amazing pictures with those um i had started out with an slr like many people do and then after that i got an astro camera that was a one-shot color and it didn't work very well and whether it was my own inexperience or something else i can't say but i never used it for very long but i can say that the pictures that i see that people take with some of these uh multi you know multi-band uh filters for their color cameras the cameras produce so amazing images with them do you do you know any differences between the expensive filters and the less expensive filters the the thing that seems to come up most often is uh haloing a brown and reflections things like that around bright stars bright objects especially um i've i i believe in buy once cry once so i i just bought astrid on filters right out of the gate and that's what i've been using i haven't had any problems with them but uh the people who complain of um uh the people with the less expensive filters seem to be the ones complaining more about uh haloing i don't know i don't know what any uh of the experience of others has been like but that's sort of my understanding thank you thank you now you were going to show us some other stuff i think we're through with the conversations over there but if you've got anything else guys be sure to just type in your questions over there and we'll get to them but let's see some image examples okay all right so uh these are some of the images that i've that i've taken and these are all i've i've i've taken out all the ones that i've done at uh at my dark site these are all just backyard examples i'll start by showing you some of the broadband uh ones okay so these are just going to be rgb or lrgb and and i want to say up front that the struggle um in processing these images is controlling the noise and controlling the gradients the noise and the gradients that is a problem for almost every image that i process but especially for my broadband images but having said that it's not an impossible situation it just requires a little bit more work so here's uh here's uh m108 and m97 so it's the owl and the surfboard and this is an image that i got i think over 2 000 luminance frames they were 15 second luminance frames but there was 2 000 of them and it did a a good job of knocking down the noise what uh the problem with this image was the gradients uh there were some really powerful gradients that had to be tamed in order for this image to be produced but the noise was great and the color turned out uh pretty great too so i was happy with that here's uh here's m101 i took this with an eight inch sct and i think noise was the big issue um with uh with this one um markarian's chainsaws galaxies uh galaxies from a light polluted site are a little bit challenging so i had gradients and again noise uh despite having a decent amount of integration on this one um okay and i mentioned earlier that uh that i admired all the dusty pictures that people take from their dark locations well here's uh here's pleity's m45 uh from my backyard and you can see some of the dust in the back i think i did capture some of it but it's nowhere near as uh you know as detailed as as what what can be seen but you know what i did it i and i did it to the best of my ability for what my sky would allow and i had a lot of fun doing it and and that's the bottom line so this is the image that i was able to produce uh from from my backyard to this one um i showed you some of the sub frames from this one earlier this is the uh the m31 finished and i think i got over 20 hours of integration on this one main issue was gradients and i also noticed since i've shot this target from a dark side as well i couldn't bring out some of the you know some of the faint nebulosity right out here at the edge of the galaxy like i can from uh from my dark side all right some narrow band examples uh here's my uh here's my rosette this wasn't a particularly long integration so uh noise was a factor here um uh gradients not not quite so much and this is a hubble palette or a modified hubble palette whatever you want to call it um okay and this is the a wide field view of the bubble nebula which is up here lobster claw nebula again kind of modified hubble palette and you'll notice that i i tend to shoot objects to the north whenever i can just because that's the direction that's favorable in my sky um i like to experiment with color palettes this uh is the california nebula and the appearance of this nebula has always been one of um a flame or fire to me and i noticed by uh inverting the color channels for um hydrogen and sulfur hubble palette is usually uh sulfur uh hydrogen and oxygen for the red green and blue channels respectively so i inverted the uh the uh hydrogen and the sulfur and it came out this neat um the orange flame like color so so i went with it i i felt like it worked with the flame-like appearance of it this is the north american nebula and the pelican nebula and i got quite a lot of data on it and it's a bright object and honestly this one didn't pose that much of a processing challenge um hubble palette all right i tried my hand uh not too long ago at a planetary nebula this is the the quintessential planetary nebula um m27 and it's a bi-color image hydrogen and oxygen is what we're seeing here and you can just make out um you could just make out the faint outer shell and i took this one with my um 10 inch newtonian all right and alex i think you might have asked me about this earlier this was an example of maybe what the limitations of narrowband uh are and this is the the bat all right the bat nebula and then the squid nebula inside there and the bat nebula is very heavy in um hydrogen and hydrogen alpha and the bat excuse me the squid emits light in the oxygen 3. again bi-color image and i collected quite a bit of um uh data for for hydrogen alpha but i really went what i thought was overboard on collecting data for uh for the squid and i got over 20 hours and that seemed to me like it should have been enough but uh you know try as i try as i might i just could not bring out the detail in the squid like uh you see images you see examples of this online and the squid just is this incredible you know three-dimensional almost solid-looking object i just couldn't do it um you know it was just this is all i was getting and no matter how much integration time i threw at it it just didn't seem to come out any better so to me this says that maybe they're even with narrow band filters there's a limit to what you can do so but like i said before i'm still having fun and that's what matters so i'll continue to take pictures of this and maybe i'll try my hand at it again but i just wanted to show you that and this is um this is one that i recently completed elephant trunk nebula hubble palette taken with my 10 inch newtonian and my cmos mono camera so in about 22 hours integration on that all right so uh let me wrap this up so in conclusion uh light pollution hides the night sky uh from all of us and it's a it's particularly bothersome for people who want to take pictures of deep sky objects to overcome the effects of light pollution for astrophotography you have to optimize your signal-to-noise ratio and there's three ways of doing that uh you can collect photons efficiently or more efficiently with a faster telescope and a sensitive camera you can collect lots of photons by stacking as many subframes as you can really accumulating your exposure time to minimize that noise and to enhance that signal and then for certain objects collect only the the photons that you are interested in the photons from the target with the use of narrow band filters maximize your time on target using an observatory or peer or if nothing else find a way to leave your portable setup out for multiple nights you will not believe the difference in the amount of data that you can acquire hand in hand with that automate automate automate we have some fantastic session software out these days get one learn it and automate image around a new moon if you can i image from fourth quarter or from excuse me last quarter through first quarter pick a target that makes sense in your sky and then finally invest in yourself by uh sharpening those processing skills and there's a lot of great resources to do that and that's it that's all i have thank you glenn um we did have a question come in could you um you went mentioned earlier about the gradients and uh edwin wants to know a little bit about what gradients are jeff answered the question a little bit but um maybe if you could say from as a presenter from your perspective what what a gradient is can you still see my screen uh yeah yeah we're still well wait a minute i don't know uh yeah you were just looking at your screen okay the youtube delay tonight is like 25 seconds or something like that which is which has been really strange i've made a few comments on your presentation before you made the presentation as a matter of fact oh god i got it okay well let me jump back let me jump back in at this point okay so this was uh when i was showing you the effects of stacking and i want you to focus down here on the um you know kind of the right lower corner all right and for this object or for this session i mean that's just where the light pollution was and that's one frame okay two frames the object's getting brighter the object is getting brighter but look at the look at what's building up over here can you see that and over here it's getting much brighter in this corner than it is elsewhere in the picture and then finally by the time you get to 200 frames i mean this is almost as bright as the signal coming from the object itself so that's what a gradient is and there's one other example that i think would be instructive uh here you go so uh all this green stuff over here that's all part of that's unwanted light that is light that is coming from the sky glow it is not coming from this target all right and that is what we want to get rid of when we process these images that is the sky gradient that uh that one must deal with when dealing with light pollution does that answer the question that does answer the question but i'm going to extend that one's question a little bit what do you do in general about gradient how do you get rid of them in general besides taking more pictures right at some point you have to deal with it in your processing program and there are dedicated tools in both photoshop and pixinsight astropixel processor and others that tackle these gradients and there's um uh i i use in pix insight i use dynamic background um extraction uh that process uh called dbe you'll hear it referred to and what that process does let's say i've i've got this picture in or this image in pixinsight it asks me to place little sample points um it asks me sorry about that uh it asked me to place sample points at various places in my uh image so i'm going to put little samples over here because that's some ugly gradient over here and over here and i try to avoid the area where i have useful signal okay so that would be all this red stuff and then i hit the uh you know i hit the do button or the process button and the uh the software looks at all the sample points and makes a determination about how much of that um is from uh light pollution or or you know unwanted gradient and then it neutralizes it it will subtract it out and it will spit out a version of the image that will have this ugly blue color gone and the background should hopefully look a lot more neutral and you can do that and you can do that in photoshop i think there's gradient exterminator or something like that i i'm not a heavy photoshop user but um there's some there's some great tools out there okay great and this is tim can i interrupt you for it with a question please hey tim yes please do um so i i don't mean to put you on the spot but last week uh adam block was on the show i don't know if you watched it but he talked about using the normalized scale gradient uh as a way to to combat gradients and at least make a make it a consistent uh gradient and not not a more complex one i've never used it i was wondering if you had and if you had any experience with it i have not and i'm halfway through last week's show i still have to finish it to see what uh adam said but um i intend to try it thank you yep yeah well the other thing you have on that image uh that green we also have scnr yes will neutralize this almost instantly the other thing and this is really a good example of it uh emission nebula when you're that tight on it the the nebulosity and the dust fill the screen and you've got to be really careful yes about what you subtract and what points you use it's almost better i would say it's almost better not to do it than to remove some structures in there which are part of the emission no i i agree and and there uh in fact i didn't use it that last uh example image of the elephant trunk that i showed you the one at the end of the talk i i didn't use it at all on that and for that very reason because everywhere i looked there was nebulosity and i noticed that when i was first starting out i put i put samples everywhere on my image and it was just peppered with with samples all across the gradient and now i will either do as you just said i won't you know won't do it at all or sometimes i only will put you know two or three samples um on the image just to be as to handle it as gently as possible well terry and i have some interesting discussions and i think we all start out with dynamic backgrounds uh with putting on literally hundreds yeah exactly and use a little tool ten per row and plenty growth and of course that makes a complete mess and the reason we don't do it anymore is that gradients are big right they're not small and you're right a few well-placed points uh will have it do its job i think in this image if you just use scnr yeah i would probably wouldn't muck around with uh dbe at all right scnr can be detrimental to narrowband images if you have a lovely teal in there right we'll change the it will change the color that's not correct but just just be careful when you where you use each tool that's all and um and when i approach him just to just to finish up on that when when i approach my processing i will uh you know i'll i'll try scnr and then i'll try another one and i'll try you know a different technique with dbe and um you know i'll trial a bunch of things and see which one works for best for that particular image and sometimes it's a tool like scnr and other times it's dbe and other times it's uh don't use any of those we've got a question from glenn for glenn only he only like one n in his name how dare he uh anyway uh he says do you use any light pollution filters for rgb i don't shoot one shot color so when i think light pollution filter in the context i think that he means it i think that applies more to a one shot color camera they do make specialized light pollution filters for those kinds of cameras um but in essence i mean a narrow band filter or any uh i mean a narrow band filter in particular i mean it's a very very strong light pollution filter you're filtering out tons of light pollution and uh you know that's not necessarily uh what you're looking for but in in effect it's doing just that it's filtering out all the light pollution and showing you just the signal from your target okay yeah they they're um you have to understand what's going on when you're filtering with a light pollution filter you're letting some stuff in and other stuff you're not letting in that's right and with the narrow band you're already not letting nearly everything in right you've just got one very strict small strip and i will say for a uh for a light pollution filter those probably had more relevance back in the days before led lighting uh when you had you know sodium um what do they call it uh sodium lighting oh yeah there were special right right there were specific parts of the visible of the spectrum that the that kind of lighting lived in and these filters would cut that out but now with with broad spectrum led lighting i think it's less effective yeah and though the world of tri-band and duo-band filters for one-shot color is is much different than the world that we're talking about with mono and narrow bench so some of the concepts apply but there there are different things going on and then after you've cut out x y z bands of the spectrum then you've got to get through the barometrics which is already cutting out other parts of the spectrum so it's it's i i don't have enough experience to comment on the effectiveness of it maybe out there somebody does have such experience and they can offer a program on the astro imaging channel there you go there you go yeah are we doing we got all the questions i think we're all put up right eric i think we i'm looking i don't see anything new and we've got a few congratulations nice shows showing up already awesome thank you and so i want to thank you for for putting on the uh presentation uh if you could stop sharing your screen and just come on back live to us that'd be that'd be cool and um the um what else am i gonna say the i don't know so i think we're ready to get ready to call it a night we got everything taken care of don't forget we need you to turn in your your nebula that you've been taking pictures of we need you to go on over and catch up on um on uh the workshops get eric's data process it and show us how you can do things um and i think we're we're good tim i think you're in charge tonight uh glenn thank you so much for being here tonight and thanks for having your services and uh i should tell everybody here it might be a little personal but uh glenn remarked to me uh i asked him to do this show i don't know a couple months back and he says yeah i mean yeah i guess i can do it and you guys can do it too i mean all of you can do a show uh all of you've got something you can share with other people um you're all bright people you all ask your imagers so you know how to handle stuff um volunteer to give a show it you can help people a lot okay thanks everybody tim taking us take us out

Channel: The Astro Imaging Channel

Views: 1,863

Rating: 5 out of 5

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Id: d8iv-N0U7Ec

Length: 79min 20sec (4760 seconds)

Published: Sun Sep 12 2021