Filters for Deep Sky Astrophotography

One of the most confusing aspects when I started astrophotography was filters. There are so many choices and I just really didn't know what to invest in. Do I want a moon and sky glow a CLS a UHC interference narrowband? There's a lot of terminology and what I hope to do is really break it down for you in this video so you can make an informed decision before buying your first filter Hi everybody this is Nico from nebula photos.com here first thing I want to say is that this will be the first in a series of videos about filters and this topic was chosen by the great community of astrophotographers I have over on patreon if you're interested in joining us it starts at just one dollar a month so this is a huge topic and with this video I'm just going to be scratching the surface so I might gloss over a few things my goal though is to make this approachable explain a little bit about how filters work and also just to dispense some practical information that will help you buy your first filter if you're interested or really let you know if you need to buy a filter if you ever feel lost with all the terminology I've made a glossary and a summary of this video and you can find that on my website the link is in the description right below here so before we get into the more technical part of this video where I really do a deep dive on what filters are and how they work and camera technology and all that I thought it might be a good idea to just provide answers to a few of the big basic questions about the use of filters for astrophotography and I'm going to be mostly focusing on DSLRs you can think of this is just a quick summary of the topics I'm going to cover in this video but I'd encourage you to stay around for the whole thing because I am going to go into much more detail so that you can really understand the reasoning behind any advice that I give so question 1 do I need a filter the quick answer is probably not so why am I saying that well a normal DSLR which is what I'm assuming most of you are using out there already has a number of filters built-in that will give you great natural color for astrophotography with the right processing the only downside to the filters built into a DSLR is the IR cut filter also called the hot mirror will sometimes be a bit too aggressive and not transmit that each alpha emission line very well and what that means is it makes shooting red nebulae a little bit more difficult but an added filter so let's say we add this astronomy CLS in front of the DSLR that's never going to get you more HHH alpha sensitivity so let me repeat that an added filter to a stock DSLR will never get you more H a sensitivity to increase the H a sensitivity of a stock DSLR we need to modify it by removing the IR cut filter and so this one is my full-spectrum 60d so the in this case they they completely removed the IR cut filter and replaced it with a clear piece of glass of the same thickness so that it reaches focus that's called a full spectrum mod because we're now letting all the wavelengths of light hit the sensor including UV and infrared not just the visible part of the spectrum if any of this is confusing because you're hearing these some of these terms for the first time don't worry I'm gonna explain this stuff in more depth later in this video but the bottom line is if you have a full spectrum camera either a modded camera like this DSLR or something like a qh y or z wo camera that use full spectrum then you might need a filter to block the IR the reason is that star bloat is unavoidable with a full spectrum camera that passes the infrared and this is due to the fact that the infrared focuses at a different focal plane than visible light if you look at some old manual lenses you'll actually see that they have infrared focusing marks but for everyone out there that just has a stock DSLR or mirrorless camera you don't need a filter you still may want to get a filter and the main reason you want you may want a filter is to improve contrast of certain deep sky objects mainly emission nebulae so by blocking part of the spectrum you're then blocking a lot of light pollution sources and what that does is it darkens the sky a lot the the sky is usually quite bright because that light pollution is is hitting the atmosphere and then coming back down into your camera and so by improving the contrast by darkening the sky then certain things like emission nebulae will really pop and it'll look like they're getting brighter but it's really just that you're improving the contrast between the sky and the ned delay and so this video will go into all the different types of filters that can help improve contrast by blocking some light pollution and some of the major ones are the neodymium also called a moon and sky glow filter often ACLS city light suppression filter we'll talk a little bit about narrow band filters do I have a example here the El enhance is not quite a narrowband filter but it's sort of the right idea if you're just starting out and you're interested in deep sky photography I would not recommend behind a filter at all especially before you buy a tracker or a mount it makes no sense to buy a filter before you buy a tracker or mount the cheapest trackers that I know of like this move shoot move unit are about the same price as a filter like this El enhance I mean they're really pretty similar in price and there are a number of reasons to get the tracker first one untracked you limited the very short exposures if you've watched some of my other videos you'll see that we're taking exposures that are just a 1 to 5 seconds long at most and when you're taking such short exposures you'll technically be underexposed of course and so we don't want to exacerbate that by letting in even less light by blocking possibly valuable photons that are hitting our sensor so - in terms of getting better shots the tracker is just going to be much more important than a filter a filter is like a nice thing to have maybe once you've have the star tracker you get how to use it you're doing longer shots with a with a telephoto lens or maybe a small telescope at that point then the filter will make a lot of sense one note here before I move on to the next question I said telephoto lens or telescope is where it makes most sense to get filters and the reason I say that is because filters can also pose serious challenges when used with really wide-angle lenses and it's due to the way that those lenses bend the light and this can result in basically band-pass issues and you get funky stars so I'll go into more detail on that later on in the video but just keep in mind filters probably work best with more like telephoto lenses and telescopes and at that point you really need some kind of tracker it doesn't make sense to try to use a telescope untracked question - where does the filter go so if you're coming from the normal photography world you may think this is a dumb question you're used to screwing or mounting with something like this 100 millimeter holder you're putting the filter in front of the lens and there are a few astrophotography filters designed this way like this Heide and are not to say nano Pro clear night filter so this is a hundred millimeter square filter I put it into there and then I can put it in front of the lens but most people don't want to put their astrophotography filter in front of the lens or tell scope because it just is doesn't make sense in terms of how big a filter you have to buy to cover the front objective it gets very expensive if you wanted to do that so instead we typically put the filter somewhere between the back of the optics and optics just means telescope or a lens in between the back of the optics and the cameras sensor so the sensor is in here in the camera body so there's gonna be some room somehow between here and the back of the optics and we we put the filter in there on a telescope when you get into really advanced setup so you can actually put a use a filter wheel or a filter drawer and you just put that in the path between the end of the focus or in the camera and that makes everything really convenient for switching out filters and that's what I have going on here with my mono setup but for DSLR what is much more common is to get a 2-inch filter and to screw it into the field flattener or some other accessory that is then attached to your camera and your telescope so it's right in between the back of your focuser and your camera now if you don't have a telescope are you out of luck well maybe maybe not because many filter makers actually make very customized filters they're called clip-in filters and they actually just clip in right into the camera body I have one here by astronomy this is the l2 UV IR block filter and I'm using that with my full-spectrum 60d and that you just push it right in and it's a custom fit right into the camera body like that and one of the reasons that I tell people when they're asking well what can kind of camera should I get with that for astrophotography I'm just starting out to get a Canon or Nikon DSLR buddy these are the go-to brands for me is because of the support there's so many accessories and filter makers that know people use Canon and Nikon DSLRs that you're gonna just get so many more choices if you want a clip-in filter you're gonna find plenty of choices for like this like cannon crop sensor aps-c sensor body and a lot of choices for Nikon too but if you're a Sony shooter fuji olympus panasonic then you're not going to find that many choices maybe still some but not not nearly as many clipping filters are usually a little bit more expensive in my experience than the equivalent round mounted filter i think the reason is that they're a little bit more of a niche item but they're usually are worth it to me because they open up a lot of new opportunities because we can now use camera lenses you just can just screw on a camera lens just as you would normally well with a two inch filter like this there's no place for it to go because the camera lens mounts right onto the camera body and then there's no place to put in the the two-inch mounted filter one of the most popular makers of clip-in filters is astronomic and i've noticed that they recently released a new line of very thin clip-in filters for wide-angle lenses called their xt line to address band-pass issues basically where the light gets so curved that it doesn't the filter basically is filtering out to some of the lights and then you get these weird effects like triangle stars and things like that I haven't tested these XT filters yet but they're the only astrophotography filters I know of you're dressing this issue of wide-angle lenses and what can happen with the light so if you know of any other filters that sort of have a novel way of addressing that maybe I think this high de nano pro clear night is probably meant to address that to where you put it in front of the lens so that's another way to go all right so that's it for where does the filter go clip in if you have a telescope you can use a two inch or there's a few filters that can go in front of the lens third question I want to filter what filter should I get I'm gonna repeat myself here and because it's important and I just want to make sure everyone gets it if you're a beginner with just a DSLR and a tripod and you're just taking untracked shots you don't have a tracker or a mount or a telescope then I wouldn't recommend getting a filter just go without a filter shoot for a while and see what you can get because you can get a lot of really great stuff with just the way that a DSLR is designed which is gonna give you natural color anyways if you're a bit more advanced though and you own and you already know how to use your you know equatorial mount or your tracker and you're specifically trying to improve the contrast of emission nebulae so that they pop a little bit more then the choice gets more complicated budgets a big concern and you're trying to get it like a sum of somewhat of a value filter I would recommend this Bader neodymium filter this goes for around a hundred and fifty dollars for a two-inch filter if budget is less of a concern and you really want to just bring out those nebulae with really improved contrasts at all costs you don't care about accurate star color you're really just trying to make the nebulae pop with your color camera then a duel or tribe and narrow band filters what I'd recommend on the low end we have something like the opto long L enhance and on the high end something like opt z' radiant triad if you're asking about specific brands or filters that I personally recommend wait for future videos because I will be doing reviews the next video I'll be releasing is my first review shootout and with four popular light pollution filters compared and I also hope to do one on you know narrow band filters for color cameras and and other kinds of filters to at some point fourth question how light polluted should the skies be before I really consider a light Ellucian filter and unfortunately I don't have an easy answer to this one this question may be used to be easier because light pollution filters were more effective when cities used mostly high pressure sodium lamps and some mercury vapor street lamps and they used those sort of orangish amber street lamps almost exclusively but with the huge move in recent years two white LED light I can't answer this in a super straightforward way but I can say that my own testing with light pollution filters is that show is that they change contrast and color balance of course regardless of whether you're shooting from a city location or a rural location and so you might like the effect no matter how much light pollution you have it's really a personal thing I'll have lots more about this in my next video which is that shootout but I just want to point out here that if people online are saying you should never use a filter and this or that situation you really have to ask yourself has this person done the work of actually testing and all those situations that they're talking about and how similar is that person's gear to mine because lots of things can make subtle differences including the camera that you use and particularity zuv your light pollution and how much there is but also what that light what those light pollution sources are made up of whether they are more something like high pressure sodium street lights or white LED street lights okay that's it for the basic questions now let's really dig into this and get a better understanding of how filters work and before we can talk about filters we first need a basic understanding of the digital camera any digital camera has something called the image sensor if I flip up the mirror you can see it right there image sensors are pretty similar no matter what camera you have the basic way they work is a light wave travels through the optics it gets focused on to the sensor plane and when it hits the sensor a number of things happen the sensor is a really complex set of electronics filters and silicon and because light is both a wave that's how we've think of it when we're focusing it or focusing it on different colors that kind of thing but it's also a particle and so the particle nature of light is what we call photons the sensor is a photon counting machine basically so at each photo site a number of photons are hitting that photo site and it's converting those photons to electrons which produce an electrical charge and this is how we get different brightness levels at different pixels and it makes a full picture those charges are stored in something called pixel wells and so you could have one pixel over here that's that's holding a charge that is twenty converted photons and another pixel well over here that's a charge of 300 converted photons and then that's how we get the full picture with all the different brightness values however sometimes that picture isn't bright enough so we have a gain multiplier sometimes this is called ISO and a DSLR basically just amplifies that analog signal before it gets turned into digital information by an analog to digital converter that's then read out onto the computers board like a mini computer and that's where the digital information is transformed into a file a raw file or a JPEG and finally passed on to your memory card or to your laptop for storage if you're using a mono camera like many astronomy cameras DCD that kind of thing it Mesa Kaleem eanes that you're just using a bear sensor the only thing that's in front of that sensor is the cover glass with a coverslip and it's just a clear piece of glass should be anti-reflective and it protects the sensor if you're using a color camera sometimes called a one shot color camera meaning you're getting a full color image out of it basically any DSLR is a one shot color camera then in front of this bear sensor is yet another thing called a color filter array sometimes you'll see that CFA for color filter array and this is a filter that's already built into your camera that is is a very complex filter where it's a pattern of red green and blue and so what it means is that one pixel will only be reading red light or will only be capturing red light the pixel next to it will only be capturing green light and the pixel down from that will only be capturing blue light and this fixed pattern is all over the sensor the most common pattern for that today is called the Bayer array named after dr. Bayer from Eastman Kodak who invented this whole concept and the Bayer array uses two green pixels for every one red and one blue pixel and the reason for double the green pixels is because human vision is actually more sensitive to that part of the light spectrum the actual raw data from an imaging sensor with a color filter array looks like this notice it's grayscale it's black and white this is what a sensor actually records just shades of brightness shades of gray and it's only through a computer algorithm called debayering that we get an approximation of the color that was recorded at each photo site at each point of the sensor and so you can think of this kind of color reproduction as a lateral color filter it's putting the colors all over laterally across the sensor you can also do something called vertical color reproduction you might have heard of something called a Foveon sensor they're only really available in like I think Sigma cameras but it's basically the idea is let's but the the red green and blue filter is all on top of each other on top of the sensor and record information that way and we're basically doing vertical color reproduction whenever we do a mono sensor - we just shoot the red green and blue filters separately and then combine them in post-production and that kind of working with a mono camera and shooting red than shooting green than shooting blue is really only practical for objects that don't move much like deep sky objects it doesn't work for fast-moving objects like comets or people or anything like that okay I know this is a lot of information one more thing though to mention about how the camera is set up is that the part of the light spectrum that were typically most interested in collecting is the so-called visible light spectrum everything that we see with our eyes is what we call a visible light spectrum but just to the one side the blue side is is ultraviolet and to the red side is infrared light and we typically don't want those in our pictures because they can mess things up early digital cameras would sometimes let in that infrared and you'd have a really weird color response because of it on some things like you get purple fire so what they started doing with digital cameras is they started installing something in the filter stack called a hot mirror or IR cut filter that would block this infrared so you'd get natural colors especially for daylight photography only problem with a hot mirror or IR cut filter is that different DSLRs will have different IR cut filters and some of them are quite aggressive and how much of the the deep reds they're blocking and many of them will block much of the h-alpha response so your red nebulae won't come out that great because your camera filter is blocking so much of it and so many people aren't happy with their DSLRs stock performance stock camera so they get their camera modified and so what you do when you your camera modified is they go in either you can do it or you can pay someone to do it and they remove that hot mirror and either replace it with a clear glass filter this is called a full-spectrum camera when we replace the hot mirror with a clear glass or a they replace it with a different IR cut filter that's more sensitive to the AJ and we call that an H a mod and the reason that with a full-spectrum camera that they replace that hot mirror with a clear piece of glass and don't just take it out entirely is so that the focus focusing of the camera stays intact okay so modifying your camera the point is to let in more H a because normally the hot mirror is is not transmitting as much of a ETA the two advantages of buying an astro camera are one that most Astro cameras are usually either full-spectrum or H a modded and two they have cooling which I'm going to get into later on in other videos so where am I going with all this well IL is talking about cameras and we're talking about filters well the important thing to keep in mind is that when you're choosing external filters for deep sky Astro photography we first have to consider the kind of camera we have and what filters are already present in the camera design so some filters like RGB filters red green blue filters make sense to buy for a mono camera but would not make any sense to buy for this camera because the RGB filters are already present in the cameras design through that color filter array for this series on filters I'm gonna be limiting the scope a little bit because I'm only going to be covering so-called one-shot Cutler OSC cameras which includes color astronomy cameras DSLRs and mirrorless again a one shot color camera means that the color filter array often a Bayer filter is intact on the sensor if you're interested more in mono and filters check out my intro to narrowband video series so we've gone over cameras and sensors let's move on to the types of filters most external filters you'll buy for deep sky astrophotography are so-called interference filters meaning they interfere with the light wave usually by reflecting part of the spectrum away the other main type of filters is an absorption filter and an absorption filter instead absorbs a large part of the spectrum and only passes the desired colors absorption filters are dyed filters and they can only pass that one section of the color spectrum meaning a blue filter can only pass blue right well an interference filter they get a lot more specialized and they can carve out multiple parts of the color spectrum to pass so for example you could design an interference filter that passes some blue and some red but no green so for the rest of this video all the filters I may be talking about are interference filters but we can break this down a bit more one type of interference filter that's pretty popular is called a CLS filter stands for city light suppression and for a long time most city street lights were designed with either mercury vapor or more commonly recently high-pressure sodium bulbs and this kind of street light is a fairly warm colored amber colored it emits in a fairly narrow band pass and it's mostly yellow orange or you can think of it as a part in the green if you if you're thinking red green blue the CLS filter was designed to block those kinds of lights and those kinds of lights only really so that those wouldn't interfere with our astrophotography and we could therefore get better contrast in the city but the problem with the classic CLS design is that most cities are now moved to LED street lights which are often more full spectrum they're much bluer and they're much harder to block with just a simple filter another type of filter though is called a selective bandpass filter other names for this kind of filter include a moon and sky glow filter or simply a neodymium filter named after the element neodymium that this filter is made out of or it's it's made out of glass but also the neodymium is somehow put into the glass to get this unique selective bandpass comparing it to the CLS you can actually see that it lets in a lot more light but what that means is that you're not blah thing is much like you're not going to get that really high contrast but you're also getting good color balance probably or a little better color balance at least and that means that you'll get more colorful natural colored stars you know another kind of filter you may be familiar with is the UHC ultra high contrast UHC are mostly designed for visual use I usually don't recommend them for astrophotography but I mention them here because they're yet another kind of selective bandpass filter the people often use to combat light pollution lastly a narrowband filter or a mission line filter is meant to really just isolate the spectral lines that emission nebulae shine in if you have a single narrowband filter it's just isolating one mission line like H alpha or o3 if you have a dual narrowband filter then it's trying to isolate like oh three and H a usually a tri-band filter you know could be oh three H a and s two so forth and these types of filters can be really effective for shooting nebulae but they're not useful R usually for broadband targets like galaxies and stars unless you're trying to do something quite specialized like isolating the nebulous regions in a galaxy I've done that with like m101 you can see this is m1a1 shot through and H alpha filter and that's a bit of a side because I used a mono camera but with a one shot color camera what I've noticed when shooting these types of filters is that the stars that should be yellow and orange usually just look white or red and the stars that should be blue usually white or green you can that's easy to understand when it's cutting out most of those star colors narrow band filters are typically the most expensive type of filter but they're also the most effective ad blocking light pollution so they are what I use in a portal 9 zone I use narrow band filters plus a mono camera if you can't afford that it really is the best way to combat light pollution and do astrophotography so given these filter types what kind of filter is right for you if you're most interested in just getting natural color but also improving your contrast a bit then something like this Bader the Dimmie em is what I'd recommend if you're really into the narrowband look and you're trying to really isolate the the emission nebulae then something like a opto long L enhance or even one of the more expensive dual narrow band filters might be what's right for you in 2020 I usually don't recommend a CLS but it really is important to note that it may still be applicable to you because not all cities and towns have switched over to white LED lighting so a CLS might actually still make sense the next important consideration when choosing a filter is how you plan to mount the filter filter mounting can limit your choices and the filters that you're able to purchase the smallest filter size for astrophotography is the one and a quarter inch threaded filter and the named one and a quarter inch filter is is really just to make it clear that these work with one and a quarter inch eyepieces but they'll thread into a one and a quarter inch eyepiece like that the actual filter thread is one 1/8 inch in diameter at 42 threads per inch similarly a two inch filter is not actually two inches in diameter it uses 48 millimeter diameter threads so this will work within any m48 threading and the threading spacing is 0.75 millimeters typically but again they call it a two inch filter because if you add a two inch eyepiece it should screw right in like that but even though these are both astrophotography filters we use these conventions for visual observing but usually visual filters and astrophotographers filters are different animals one thing you'll find out quickly though when you get into telescope base tests from photography is there are literally dozens of different filter thread standards so putting together an imaging train often involves you know I need to from m-68 to m54 248 and I need these custom adapters or special things from Germany so it's a nightmare but really with mounted filters the thing to keep in mind is two inch filters use 48 millimetre threads and one and a quarter is is basically just a custom thing that's very common throughout a lot of just different filter mountings when you look at the prices of these things you'll notice that the one and a quarter inch filters are a lot cheaper than the 2 inch filters and it makes sense why because they're much smaller and so you might think well I'm going to save money and buy these one and a quarter inch filters if you're using a DSLR though that's not going to work if you have a micro four-thirds camera this might actually cover the sensor area but with a with a DSLR no matter how close you put this one and a quarter inch filter to the sensor you're still going to get extremely netting with either a crop sensor body or a full-frame body so it's you really need to either move up to a clip in filter or a two inch threaded filter in terms of filter availability between clip in filters mounted filters that work with telescopes mostly and filters that go in front of the lens I would say that the camera to get if you want the most options in terms of a DSLR is a crop sensor Canon body aps-c Canon body but at some point I hope to do more of like a filter finder kind of tool that will really help you find a filter based on your gear for now though hopefully this breakdown is somewhat useful this size filter is the most common but it's only gonna work if your sensor is small enough Micro Four Thirds are smaller the most common kind of filter to get it's sort of more versatile with all kinds of telescopes and camera systems if you're not sure if you're gonna stick with the DSLR and then eventually move to an astronomy camera is the two inch threaded filter which again actually use as m48 threads just as a little preview for the next video coming up in the filter series I'm going to be comparing four different affordable and fairly popular astronomy filters for light pollution the cheapest one being the SV Boni CLS we also have the astronomy CLS the Bader moon and sky glow neodymium filter and the opt along L pro so we're going to be comparing these four in a lot of different situations including with a stock DSLR with astronomy camera in bordel four and bordel nine all kinds of different situations to give you an idea of what to expect from these filters and we're gonna be comparing them head-to-head and see which one comes out on top till then this has been Nico Carver from nebula photos.com clear skies everyone

Channel: Nebula Photos

Views: 37,618

Keywords: astrophotography, astronomy, narrowband, narrow band, science, filters, dslr astrophotography, astrophotography filters, astronomy filters, optolong l-pro filter, optolong l-enhance, baader neodymium, svbony filters, light pollution, cls, interference filters

Id: ys-28z4qTYw

Length: 36min 1sec (2161 seconds)

Published: Mon Jul 20 2020