Huge Telescope. Tiny Sensor. Why?

This video is sponsored by Squarespace.  Tonight I'm using my biggest telescope   and my smallest sensor. But why? Well because  I'm going after a deep sky object that is tiny   in terms of apparent diameter. Tonight I'm going  to attempt to photograph the bright core of the   Cat's Eye Nebula in the constellation Draco and  this is by far the smallest deep sky object I've   ever attempted and so I'm going to throw out  all the usual methods that I normally use for   Imaging and processing and try  something completely different,   completely new to me and bring you along for the  journey, but also explain a little bit about why   I'm doing this and what I'm doing. So my name is  Nico and you are watching nebula photos [music] Hey, so if you're new to the channel, as the  channel named nebula photos suggests what I'm   interested in as a photographer are nebula and  these are colorful gas clouds that are in my   opinion some of the most beautiful natural objects  in the universe and it's just amazing to me how   accessible they are for backyard photographers uh  this video is not where I'd start for learning how   to capture nebula yourself I have much better  videos for complete beginners that go start   to finish and I have a playlist for those that  I'll link um but what I'm going to be doing in   this video is more of an advanced technique with  advanced gear and it's called lucky Imaging and   my reason for documenting it is there's been some  interest in my patreon community so much interest   that this past month we've actually been working  on a lucky Imaging challenge together and that's   something we do every month take on a new Imaging  challenge over on the patreon side of the Discord   and I think that's a great way to stay sharp as  an astrophotographer it's something I love about   the hobby you know to be constantly challenging  myself you know with new ideas new techniques   so what is lucky Imaging well before I explain  it I have to go take a few steps back and let's   start with the term angular resolution resolution  just means what is the smallest detail you can   resolve so for example if I put this small  bottle of Noodler's ink a few hundred feet   away if I photograph it with a telescope we  can still resolve very small details you can   even still see that it says made in USA on the  label if I instead use a wide angle camera lens   my resolving power goes way down and now I can't  even really make out that there's a bottle of ink   there on the Rock because the resolution decreased  um so that's the trade-off for getting a much   wider field of view you won't be able to resolve  very small details when you zoom in on the photo   now angular resolution is just a way of measuring  detail by describing the apparent diameter of an   object in degrees of Arc basically if you imagine  measuring the Horizon to Horizon that would be 100   180 Degrees of Arc so half a sphere and now you  can break up a single degree of Arc into 60 parts   we call those arc minutes and then if you break  up each of those arc minutes into 60 parts we   call those Arc seconds and you can then describe  the apparent diameter of anything in your field   of view using this angular resolution so now  let's get to the telescope and if you've heard   the term you know x arcseconds per pixel like one  arcseconds per pixel is a common recommendation   for deep sky imaging that's describing the  theoretical angular resolution of a telescope plus   a camera meaning you know with this scope and this  camera what is the smallest detail that can be   resolved by a pixel on the camera sensor so if you  say one Arc per pixel you're saying theoretically   you could make out a detail that's only one  arcsecond big um but unfortunately Pixel scale   is just one part of the whole solution with true  resolution because there's other physical limits   that uh will limit the actual amount of detail  that can be resolved uh and there's two main ones   we can briefly discuss them the seeing limit uh is  caused by air turbulence in the Earth's atmosphere   and the diffraction limit um is just comes down  to physics uh with your telescope size and you'll   also see that called the Dawe's Limit or the  Rayleigh Criterion it's it's entirely determined   by the aperture of your telescope how big it is  so if you want to resolve really small details   and you have very steady Skies then you'll need a  bigger telescope to do that because otherwise the   diffraction patterns of the light sources in your  photos are going to blur together and you won't   be able to make out the smallest details but the  the limit that affects way more of us uh in you   know most places on Earth is the is the limit from  your your Sky conditions you're seeing basically   when you're looking up at the night sky you know  it looks transparent it looks like there's nothing   between us and the stars but actually the sky the  Earth's atmosphere is still there um you know what   we see is a blue sky during the day uh it's still  there it's just not illuminated by sunlight but   it can still uh cause a bunch of issues for us  asap photographers you know the two main ones uh   being that it can be lit up by artificial light uh  shining up on it uh this is called light pollution   and then when you know there's more water vapor  in the sky or smoke it gets much worse and when   it gets worse we call it poor transparency so when  you when the when the sky isn't very transparent   it sort of looks like there's this like uh  thick layer of light between us and the and   the night sky and but the the more important to  the discussion today is seeing and this has to do   with different layers of atmosphere um between us  and space and uh they are all moving in different   sort of directions and at different speeds and  that's turbulence and this turbulence causes uh   a lot of blur in our images so um you can see it  if you you know if you look at the moon at high   power you can actually see the the turbulence in  the air and uh if when it's a really uh steady   night um it will give you a much clearer view now  what the professional astronomers do is they build   their observatories in places where the seeing  is typically excellent um the the best places on   Earth to do this are mountaintops you know very  high elevation where you can get above a lot of   the poor seeing and then also uh near oceans  where uh you can have um inversion layers and   laminar flow and all these terms that have to do  with basically the air currents being very smooth   and lined up now most of us don't have the luxury  of building our observatories on mountaintops uh   but the good news is there's a technique called  lucky Imaging that can help quite a bit with   poor seeing um if you're a planetary imager you  probably have already come across this technique   the idea is if you shoot uh with a high-speed  video like 60 or even 100 frames per second   there will be moments where all of the turbulence  in the air uh lines up in a way to give you a nice   clear view of space and if you're taking thousands  and thousands of frames you may get hundreds where   you're lucky and you and at least some part of  of the planet's surface or the moon's surface is   showing a good amount of detail and then when you  stack all these good frames together you end up   with a much sharper image of the planet or the  Sun or the moon um than your seeing conditions   would normally allow that's why they say it's like  beating the seeing now the faster you can make the   frame rate the luckier you'll get right because  you you have more chances to get lucky so this   doesn't translate to deep Sky Imaging very well  at least for most objects because most objects   are too dim to shoot at a high frame rate um or  or a very short exposure for instance you know if   you're shooting what would be a short exposure for  deep sky might be like 30 seconds but that's still   way too long to take advantage of Lucky Imaging  because the air currents just move too fast so   uh the the blur will be baked in at at 30 seconds  so then the question becomes okay how short do we   have to make the exposures to get the advantage  of Lucky Imaging and that's the million-dollar   question I'm sure to some degree it depends on  your local Sky conditions and things like that   but I've looked at a lot of people who have been  successfully doing some kind of Lucky Imaging for   deep sky and it seems like 1 second might be uh a  a good Target now this also might depend a little   bit on F ratio and it definitely depends on  how bright the object you're shooting is so   don't just take that one second as the end all  and Beall but that's what I'm going to be using   tonight at f5.6 uh and with the Cat's Eye Nebula  and I chose the cat's ey nebula because it has a   very cool shape and it's very well positioned  in my sky right now it's in the constellation   Draco which is uh easy to photograph if you  have a good view to the north which I do from   my backyard Observatory that I'm sitting in right  now I can see the north is nice and clear I don't   have any trees so that's uh basically the theory  part of of Lucky Imaging uh let's now move on to   the gear and the kind of telescope you want to  use is going to be your biggest fastest scope if   you have say a motorized 16-in F4 Dobsonian that  would be perfect for this uh for me the biggest   fastest scope that it was practical to use CU I  can track with it and everything is this Askar 185   APO with the f5.6 reducer now for the camera you  want basically a unicorn a camera with very low   noise but also very small pixels um and these  two things often don't go together but this one   the ATR585c from Touptek that uh they sent over  for review seems to fit the bill it's 2.9 Micron   pixels which are pretty small and the read noise  is also very low from using it I will say the   fixed pattern noise is higher than you'd get from  larger sensor cameras but there's always going to   be trade-offs like that and for the for the most  part the that doesn't really matter too much for   this kind of application um the other thing that's  useful about this camera is it has a small sensor   um you might you know it's 11 mm across 6 mm High  4K resolution for for context a fullframe sensor   is usually uh 36 mm uh across by 24 mm High and  the bigger sensors come with bigger images in   terms of file size often 50 to 90 megabytes for  a full frame while this is 8 megabytes and when   you're registering and analyzing thousands of  images that's very important it also um may be   important when it comes to capture right if it if  it's taking time for your computer to download a   large uh image and then start the next one um or  if it runs out of buffer or whatever um that can   really uh drag you down with lucky Imaging you  want something that basically Works in real time   just constantly taking images now if you don't  have a small sensor camera like this I haven't   tested this but I've heard you may be able to use  the region of Interest feature Roi in your capture   software and so that it basically only reads out  a small cropped portion of the sensor basically   acting like a smaller sensor I don't know if there  any downsides to that uh since I haven't tried it   but if someone else has tried it let me know in  the comments uh but I'm going to be using this one   and I think uh it should work well I think this  is a a good sensor size for this application okay   next up in terms of the actual capture process  the way I did this is after downloading the tube   Tech driver I set it up in sequence generator Pro  where I already have the plate solving and all of   that kind of good stuff configured so then I could  just easily focus and Center on the object using   Sequence Generator Pro which I'm already familiar  with but for this step you could use any control   program you like like that you have connected to  your mountain and Camera it could be EKOS, NINA,   APT, any of them then with the object centered and  the mount tracking on it and keeping it centered   in frame I switch to Sharp cap which is a program  that has some nice advantages for Lucky Imaging   the main one being that it can capture basically  in real time and store all of the frames that it's   capturing into a single SER S-E-R video file so  you end up with just this one efficient file with   thousands of raw images in it and it's already  optimized for this kind of work it just makes it   a little easier um and and I also found that  I was able to be pretty efficient that way I   was able to gather a bit over 5,000 frames at 1  second each and a couple hours and the resulting   SER video file came in at about 80GB and that's  that's what I'm going to try processing with Siril   and I'm using Siril for a couple reasons uh it's  very fast at registering and stacking so it makes   uh experimenting less painful and then second  unlike PixInsight or other programs can work with   these sir sequences very efficiently so you don't  have to use other programs to convert or anything   like that now I will admit there are other more  complicated methods for doing this kind of uh   lucky Imaging processing that may result in better  fin images I haven't had time to investigate them   all but two popular programs for Lucky Imaging  stacking in general that also seem to have support   for deep sky are Autostakkert which I have used  before and Astro Surface which I have not but I   hope to uh sometime in the future so anyways I'll  be using Siril is it's crossplatform it's donation   supported but uh free to download before I show  the processing let me just take a quick moment   to share a bit about today's sponsor which is  Squarespace Squarespace makes it easy to make   a website with their guided design system called  Squarespace blueprint you can choose from many   professional templates but then style them however  you'd like with the easy to use interface that I'm   showing here there is a bunch of other features  built in for example if you want to sell products   or prints of your work you can set up an online  store and Squarespace now has flexible payments   including PayPal Apple pay credit cards after  pay and clear pay so your customers can pay   however works best for them so whether you need  something simple just an online portfolio or a lot   more complex for your website Squarespace has you  covered and right now you can get a free trial by   heading to squarespace.com nebula photos and when  ready to make a purchase of Hosting or a domain   you can get 10% off with code nebula photos okay  here we are on the computer as you can see I'm   using an internal SSD over USBC has plenty of  free space over 2 terabytes cuz we're going to   need a lot of free space uh for this process all  that I have right now is a folder with the SER   file that we captured with sharp cap in it it's  about 80 gab and the first thing we're going to   do here in Siril is set the working directory  um so we just click the home button and set it   to where we have the surf file on the external SSD  of course you could do this on an internal uh SSD   as well you just would need enough space um which  I don't have okay we're now going to go over to   here we're going to use these tabs at the top here  uh starting with conversion and then working our   way through we're not going to use calibration uh  for this just cuz I even though I took calibration   frames for 1 second I'm not sure if they're going  to work too well we're also not going to use the   plot feature but all the other tabs we'll use  and so in the conversion tab here you want to go   down uh below this empty Source area to the little  plus sign click on the plus icon if you hover over   it it says add files to convert and just choose  your sir file in the lucky folder I'll click add and then we can give this sequence a name I'm  just going to call it NGC 6543 which is the   official name for the cat sign nebula and I'm  going to change it right here where it says   fits images to Sir sequence um I have tried  using fits images and the limitation is that   you're you're limited to stacking only 248 uh well  with a Surf Sequence you can stack as many as you   as you want as many as your computer can handle  so I'm going to leave it on Surf Sequence and   then this is very important we need to click the  deayer uh toggle right here because these are   color images I you know with the 585c um if you  were shooting mono of course you wouldn't have to   check that but if you're shooting color you want  to make sure to click debayer and then check your   debayer settings up here in the hamburger menu  under preferences uh it's you know they should be   set so that it automatically finds it in the  the metadata but uh just check these and then   if you have any problems you can always uncheck  this uh option and choose the Bayer pattern uh   manually I'm going to leave it on automatic uh  because I think that's going to work just fine   but I know that if I did run into any problems  I could come back here and just manually choose   the debar pattern and by problems I mean it'll  throw an error if uh or if if it can't figure   it out or uh if you need to do some kind of manual  intervention all right with those uh settings all   set I'm going to go ahead and click convert and  it will start going and the speed of any of these   steps will depend on your uh computer power I'm  using an AMD ryzen 5950 X processor uh which is   the most important thing here in terms of how fast  this can uh chunk through this data and and spit   it out uh so you can sort of see the the speed  at which it's going and we have over 5,000 frames   so I'm going to speed this part of the video up  okay that's uh done in terms of the creating the sequence so now what we can do is we can actually  click on the sequence tab up here and it loads the   first image in the preview over here I'm going to  click on uh the visualization modes right now it's   on linear which is why we're not seeing anything  except for maybe a couple little star cores and   I'm going to change it to if we try auto stretch  I think that's going to look pretty ugly uh it   doesn't look too bad but you can see that the the  cat ey nebula core which we're interested in is   completely blown out so that's not going to be as  useful I'm going to click on arc sign and this is   looking a lot better let me zoom in here with  control scroll okay and that's an example of a   single 1 second uh picture and it doesn't look  too good we can sort of see a a very blur uh   star in the center of the planetary nebula there  and maybe a tiny bit of detail but it it looks   pretty blurry but what we can do next is we can  open the frame list over here in the sequence tab and this lets us quickly um go through  any frame in the sequence and see what   it looks like so I can just open  up a uh new frame randomly by just clicking on it over here in the frame list  and I can see already just clicking on a random   one that it looked a little bit better than  the first one I think uh that one now looks   quite a bit blurrier uh I don't like that one  as much and that one looks terrible okay so you   can see in this one uh that's really blurred  right and the The star looks wonky over here   uh and we don't really see any detail on the  planetary nebula so that's obviously a bad one okay this one looks quite a bit better  we're seeing more detail the shape is better and this one's even better still looks a  lot sharper we're not seeing as much blur the uh   white dwarf in the center of the planetary  nebula is is nicely defined so once you've   found a frame that you think um looks pretty  sharp you can set it as the reference image up   here and this is just helpful for uh registration  okay with that set we can go to the registration   Tab and I'm going to use Global star alignment  I've tried some of these different ones and I   think for this this Global star alignment  is going to work well based on the number   of stars in the picture uh plenty of stars to  work with we're going to register all images   from the sequence we'll leave all the other  settings uh alone and so we're not going to   drizzle because we didn't dither so uh leave that  off and we can go ahead and click go register and you can see it shows you the stars that  it's using for registration and uh there it   goes and again uh because my computer's pretty  fast this process will go by pretty quick but   I'll still speed up the video uh because  it'll take several minutes okay you can   see after finishing registration it picked its uh  it picked a different reference image um based on   which image was sharpest um that's fine I you know  it's it would have been rare for me to have just   picked the sharpest image randomly um but it'll  maybe use that um in stacking now I'm going to   change the method of stacking to average stacking  with re rejection leave all these other settings   alone except for image rejection which I'm going  to change to weighted fwhm uh if you sort of just   hover over this it will describe each rejection  method and I want weighted fwhm because it's going   to give us uh the sharpest kind of uh result uh  based on which is what I'm really going for here   in addition to choosing weighted fwhm I'm going to  change the percentage of frames used and for this   I'm going to do an experiment where I stack this  several times with different percentages of frames   or images used I'm going to start with 15% which  you can see here is only 761 images of the 5,000   total after this is done I'll up that to 30% then  50% and 70% and then we can just do a quick uh   comparison uh at the end to see uh if we can see  any difference between these different amounts of   images stacked okay so I'll speed up this whole  process of generating the images and and doing   a basic process on them so we can get to that  uh comparison for those interested in terms of   the processing I kept this very simple on each of  the image Stacks I ran these five steps in seral   with identical settings uh to try to keep this  comparison as Fair as possible okay so to give   you an idea of the full 4K frame this is shown  at uh 1:1 pixels uh because it's actually a 4   K video and a 4K uh image so this is the uh 4K  uh processed image uh so you can see even with a   1 second uh image there's plenty of stars that  come out in a stack and uh the the core is uh   nicely defined and bright there uh no issue with  really exposure I think I could go down to half a   second which I'll I'll talk about in a second here  now let's go to the comparison and so here's with   that same 100% zoom level comparing the different  uh Stacks 15% 30% 50% 70% I can say at 100% Zoom I   cannot see any difference between these uh so that  tells you something maybe this object is too small   to to Really uh see much difference now at the  at 500% zoom on it uh I start I can see a little   difference on my nice monitor without any  compression I can see that uh we are losing some   of the finest finest uh details in contrast in  once we get into the 50 and 70% stacks and they're   preserved better in the 15 and 30% uh Stacks I am  sure that a lot of people watching this on YouTube   with video compression and everything are are  not going to be able to see any difference it's   quite possible that even if you were looking at  it on my monitor you'd be like what are you what   are you difference are you even seeing here so I  will say that uh this experiment was not fully uh   successful because it's not like a huge difference  uh in terms of uh the lucky Imaging trying to sort   of get the best uh frames um but I have a few  ideas of what to try next um in terms of further   experiments so let me show you those so one thing  I'm very interested in is shorter frames now that   I know 1 second Works um it would be cool to take  a lot more at half a second because I think that   one second there was plenty of light there to  work with um so I think I could go down to half a   second and and it might be an even sort of better  result in terms of the lucky Imaging another thing   I'm thinking about is taking the best of several  nights so increasing the pool of data um so maybe   trying to get 20,000 frames rather than 5,000 um  and and maybe I could do that in two nights with   half second frames another thing I want to try is  comparing seral Auto stacker and Astros surface   maybe others if people have suggestions for this  kind of stacking and um Quality estimation and   then uh I'm open to other suggestions for for for  further explo exploration of this topic so if you   have anything that you I'm not thinking of and  maybe you've tried deep Sky Imaging and have and   have tried something different than I have here  um I'd love to know what else I should be thinking   about just realized there's one other next step I  forgot to put on my slide which is this is what it   looks like with just uh lucky Imaging the cats eye  nebula but there's actually an extended shell that   you can get with traditional imaging so I did do  a little experiment with that and this is with 5   minute exposures uh and a dual narrow band filter  and then I combined that with my lucky Imaging   result to sort of resolve the core in there but  this could be much better because this is all   from a single night uh just like two hours of data  uh on the core and two hours of data with the Dual   narrow band filter with five minute subs and so  uh this is something I want to continue developing   and figuring out the best way to combine the  short exposures with the long exposures and so   maybe I'll do a video on that if I figure out  something good you are now seeing the names of   everyone who supports this channel through my  patreon campaign the nebula photos patreon is   the primary source of income for this Channel and  I now also do this full-time so I can't thank my   generous patreon members enough for the support if  you're interested in joining it starts at just $1   a month and every tier gets access to my  patreon Discord channels which includes   the monthly Imaging Challenge and we also meet  monthly over Zoom uh there are higher tiers with   other perks like add free videos starting at  $7 a month and of course you also get direct   messaging support with me so whether you're just  starting out and looking for advice on what gear   to get or you have years of experience I  think there's a lot that I offer through   patreon that will make it worth it to you when  ready to join head to patreon.com/nebulaphotos

Channel: Nebula Photos

Views: 33,129

Keywords: lucky imaging, Dawes limit, dawes' limit, Rayleigh Criterion, askar 185 apo, Touptek ATR585C, astrophotography, astronomy, cat's eye nebula, ngc6543, cats eye nebula, Draco, Nebula Photos, Nico Carver, advanced astrophotography techniques

Id: c_GjKHZk4Wo

Length: 30min 10sec (1810 seconds)

Published: Fri May 31 2024