Deep Sky Astrophotography

[jrista]

There is already a stars above thread, but that one seems to be about wide field astrophotography. I've been taking a bunch of photos of the comets flying through the sky lately. Only ones I was able to get a decent shot of was Lovejoy R1 (see the Comets thread).

I discovered an intriguing new technique for stacking very short deep sky frames in photoshop, one which nearly eliminates noise without affecting detail. I've been trying to stack short (i.e. 1-2 second) frames of the Orion nebula for a while, never with satisfactory results...always still too much noise. This new technique resulted in my first fairly decent photo:

• Body: Canon EOS 7D
• Lens: Canon EF 100mm f/2.8
• Exposure: 1s f/2.8 ISO 1600
• Frames: 30

I stacked the frames in the following way:

• Import as Layers to Photoshop fron LR
• Align all layers (did it manually, auto-align freaked out for some reason)
• Select first 5 layers, Layers->Smart Objects->Create
• Set stacking mode to mean, Layers->Smart Objects->Stack Mode->Mean
• Repeat 3-4 for each group of 5
• Rasterize each smart object
• Set opacity mode to (from bottom most light frame): 100%, 83%, 66%, 50%, 33%, 16%
• Set blending mode to Screen for all light frames
• Add Levels adjustment layer and correct black point, white point, and gray point to bring out most detail
• Tweak color, levels, curves, etc. to taste

[49616E]

That is an interesting work flow for it, I will have to check that out.

Most of the time I see people going in to 32-bit mode then using linear dodge (add). You can use the exposure adjustment towards the bottom of the window while you are stacking. This way should be much easier than the method you outlined since you just have them all stacked and you don't need to go through separate groups, just linear dodge add them all. After you do that you convert it back to 16 or 8 bit mode and adjust the exposure during the convert, I usually just use the exposure/gamma conversion.

Also a tip for aligning the layers, I typically use difference for the layers compared to one "master" layer. Seems to allow for more precision, especially while doing rotation to correct for field rotation unless you are using an equatorial mount.

I will attach one of my recent ones of good ole' M42. Let me know if you have any questions about it.

[jrista]

That is an interesting work flow for it, I will have to check that out.

Most of the time I see people going in to 32-bit mode then using linear dodge (add). You can use the exposure adjustment towards the bottom of the window while you are stacking. This way should be much easier than the method you outlined since you just have them all stacked and you don't need to go through separate groups, just linear dodge add them all. After you do that you convert it back to 16 or 8 bit mode and adjust the exposure during the convert, I usually just use the exposure/gamma conversion.

Also a tip for aligning the layers, I typically use difference for the layers compared to one "master" layer. Seems to allow for more precision, especially while doing rotation to correct for field rotation unless you are using an equatorial mount.

I will attach one of my recent ones of good ole' M42. Let me know if you have any questions about it.

Thanks for the 32bit linear dodge tip. I'll have to give that a try (although I've used linear dodge in the past, with 16bit int, and the results were still far noiser than I got here.)

As for the layer alignment, I actually do use the difference technique if I do it manually. I'm bummed Photoshop's registration feature doesn't work...it does some weird stuff, despite the fact that all the photos were pretty much identical except the shift of the nebula across the frame. The photo above is a 100% crop, so it was rather tiny in the full frame...maybe that's why. Without a tracking mount, I don't have the ability to expose long enough at a longer focal length.

Your photo has the benefit of being much larger in the frame. I have a telescope with an equatorial tracking mount on order, along with a t-adapter and t-ring, so I should be able to do much better in the future. The technique I outlined above is just for those who don't have the benefit of tracking their subject, or keeping it large in the frame without trailing.

[49616E]

Yeah, the linear dodge won't work at all really in 16bit mode. I hope it works out for you! I have used it in similar situations as with the focal length and no tracking as you did with great results.

As for photoshop's alignment for astrophotography.... He he. I have never had it work, even with the picture I provided I had to do it manually. It seems that the way registax does it is better where you pick alignment points, although I have not used it much yet.

My exposure times for that picture were 2 seconds, that is about all I could do at the time before field rotation started to become much more obvious (I just used an alt/az goto dobsonion). It is with a 50D at ISO 3200, so the original frames were pretty noisy. I want to say I used about 9 frames for it though. But yes, as you observed, it definitely helps to fill up that frame.

Should be a bunch of fun when you get that EQ mount!

[jrista]

Yeah, the linear dodge won't work at all really in 16bit mode. I hope it works out for you! I have used it in similar situations as with the focal length and no tracking as you did with great results.

As for photoshop's alignment for astrophotography.... He he. I have never had it work, even with the picture I provided I had to do it manually. It seems that the way registax does it is better where you pick alignment points, although I have not used it much yet.

Out of curiosity, have you ever tried DeepSkyStacker? Currently, I would have to say DSS is my favorite stacking tool. At least, it's registration process and denoising process (which can factor in dark, bias, flat, and flat bias frames) is one of the best. The only problem I have with it is tweaking the final result, which can be a real pain in the butt. Still, if you take a lower-contrast result, and do all the final work in Photoshop, the results can be quite good.

I am going to run all these photos I took through DSS, it's just a bit more time consuming (it's registration and stacking process can take a VERY long time, depending on how much you throw at it). I also wanted to play around with the Smart Object stacking modes to see what they could do. I have to say, median and mean stacking does a phenomenal job with noise removal. I bet you could do still life/landscape photography with multiple frames on a tripod at ISO 100, and stack them with photoshops stack merge feature to produce entirely noiseless images (and maybe even mitigate banding in the shadows.)

My exposure times for that picture were 2 seconds, that is about all I could do at the time before field rotation started to become much more obvious (I just used an alt/az goto dobsonion). It is with a 50D at ISO 3200, so the original frames were pretty noisy. I want to say I used about 9 frames for it though. But yes, as you observed, it definitely helps to fill up that frame.

Should be a bunch of fun when you get that EQ mount!

Not bad at all for 9x2s frames...of course, with the subject larger in the frame, you gathered a lot more light, but still, pretty nice results! Can't wait to get my hands on a proper tracking mount... 

I was in the market for the biggest Celestron NexStar (I think the 8") for a while until I realized it only came with the alt/az mount. Then I started saving for the Celestron EdgeHD 11", however finances have become extremely tight. So I just dropped some cash on the Celestron AstroTracker 114 EQ w/ motor drive. It is a super basic telescope, almost your bottom rung entry level. But, it has a tracking equitorial mount, for damn cheap, and some of the astrophoto stacks I've seen made with it were pretty decent (and all from total beginners). I bet I could slap together a little guidescope setup with a webcam and my Surface Pro tablet, and get some pretty good results. The telescope tube also has a standard tripod mount screw attached to it, which allows you to screw on a DSLR camera for wide field tracking, too. Whole setup (with the t-adapter/ring) wasn't even $250 on sale (http://www.telescopes.com/telescopes/reflecting-telescopes/celestronastromaster114eqreflector.cfm), which is a pretty good deal, and I figure it will hold me over until I can afford the EdgeHD 11" w/ CGEM DX mount (which probably won't happen until the end of the year next year at the earliest.)

[Mr Bean]

Nice pic's folks.

jrista, regarding your technique, I like the simpleness of it (not using any tracking), to achieve a great result. The last time I took a picture of M42, I had gas sensitized film, and the exposure was 1.5hrs

I'll give this approach a go in the next month, as Orion steadily rises.

[49616E]

Out of curiosity, have you ever tried DeepSkyStacker? Currently, I would have to say DSS is my favorite stacking tool. At least, it's registration process and denoising process (which can factor in dark, bias, flat, and flat bias frames) is one of the best. The only problem I have with it is tweaking the final result, which can be a real pain in the butt. Still, if you take a lower-contrast result, and do all the final work in Photoshop, the results can be quite good.

Nope, I have not tried DeepSkyStacker yet although I look forward to at some point. Thanks for the suggestion!

I am going to run all these photos I took through DSS, it's just a bit more time consuming (it's registration and stacking process can take a VERY long time, depending on how much you throw at it). I also wanted to play around with the Smart Object stacking modes to see what they could do. I have to say, median and mean stacking does a phenomenal job with noise removal. I bet you could do still life/landscape photography with multiple frames on a tripod at ISO 100, and stack them with photoshops stack merge feature to produce entirely noiseless images (and maybe even mitigate banding in the shadows.)

Yes, I have done that very thing with still life stuff (with the linear dodge add method), it works quite well in my opinion, especially if you are going to do a large print. At ISO 100 you only need about two or three frames and you get an extremely clean image indeed!

Not bad at all for 9x2s frames...of course, with the subject larger in the frame, you gathered a lot more light, but still, pretty nice results! Can't wait to get my hands on a proper tracking mount... 

I was in the market for the biggest Celestron NexStar (I think the 8") for a while until I realized it only came with the alt/az mount. Then I started saving for the Celestron EdgeHD 11", however finances have become extremely tight. So I just dropped some cash on the Celestron AstroTracker 114 EQ w/ motor drive. It is a super basic telescope, almost your bottom rung entry level. But, it has a tracking equitorial mount, for damn cheap, and some of the astrophoto stacks I've seen made with it were pretty decent (and all from total beginners). I bet I could slap together a little guidescope setup with a webcam and my Surface Pro tablet, and get some pretty good results. The telescope tube also has a standard tripod mount screw attached to it, which allows you to screw on a DSLR camera for wide field tracking, too. Whole setup (with the t-adapter/ring) wasn't even $250 on sale (http://www.telescopes.com/telescopes/reflecting-telescopes/celestronastromaster114eqreflector.cfm), which is a pretty good deal, and I figure it will hold me over until I can afford the EdgeHD 11" w/ CGEM DX mount (which probably won't happen until the end of the year next year at the earliest.)

Yeah the EdgeHD 11" would be very nice to have. Nice deal on the Astrotracker, I know a few people that have imaged with it, definitely very capable for that price. Any tracking at all is a huge improvement over a regular tripod. Should be able to play around with that long enough and get used to it till you get the EdgeHD. Maybe even learn some handy things along the way.

So although it is not a perfect experiment, I took some shots before it was perfectly dark. I tried the linear dodge add method and the mean method as you have outlined. I think they pretty much end up doing the same thing although you have different results to do your final adjustments with. I tried to do minor post production and have them appear as similar as possible although I did not do that great of a job and did not really focus on making them pretty or anything, but I think it gives the general idea. With enough tweaking I think they would be pretty much identical. I will say that I find the linear dodge work flow a little easier than all the switching around with smart layers and stacks. after alignment you just select all the layers and change it to linear dodge add and then convert to to 16bit. But that may just be my personal preference. I am glad I tried the mean method though, it is always neat to see the different ways of doing something

The first one is linear dodge and the second is the mean.

Camera: 50D Full Spectrum modified
Exposure: 2sec
ISO: 3200
Focal Length: 400mm
F:5.6
Stack of 20
100%crops

[jrista]

Yeah the EdgeHD 11" would be very nice to have. Nice deal on the Astrotracker, I know a few people that have imaged with it, definitely very capable for that price. Any tracking at all is a huge improvement over a regular tripod. Should be able to play around with that long enough and get used to it till you get the EdgeHD. Maybe even learn some handy things along the way.

Aye. Hands on experience is a necessity at some point. I had hoped to start getting hands on tracking experience months ago, but alas, things changed. And as you say, any tracking is a huge plus. I am also curious if I'll be able to figure out a way to mount my 600mm lens and camera directly to the equatorial mount. I am not sure if it will take the weight, which would be around 12 pounds I guess. With a 2x TC, I have a 1200mm "telescope", and with both TCs it is 1680mm. That is pretty decent for planetary photography!

So although it is not a perfect experiment, I took some shots before it was perfectly dark. I tried the linear dodge add method and the mean method as you have outlined. I think they pretty much end up doing the same thing although you have different results to do your final adjustments with. I tried to do minor post production and have them appear as similar as possible although I did not do that great of a job and did not really focus on making them pretty or anything, but I think it gives the general idea. With enough tweaking I think they would be pretty much identical. I will say that I find the linear dodge work flow a little easier than all the switching around with smart layers and stacks. after alignment you just select all the layers and change it to linear dodge add and then convert to to 16bit. But that may just be my personal preference. I am glad I tried the mean method though, it is always neat to see the different ways of doing something

The first one is linear dodge and the second is the mean.

Camera: 50D Full Spectrum modified
Exposure: 2sec
ISO: 3200
Focal Length: 400mm
F:5.6
Stack of 20
100%crops

Thanks for the test. Very interesting results. From a noise standpoint, they do indeed look identical. From a color standpoint, colors are a touch richer with the Median method, and stars are just a little softer, too.

The Linear Dodge Add method definitely sounds simpler. I'm going to give that a try now, with the previous photo I posted above, and see how things look. I think I may also try photographing the nebula with my 600mm lens for 1-2 seconds and stack em, see how things turn out. I figure downsampling for web should take care of a lot of the trailing.

[jrista]

@49616E: Any chance you could outline your specific LDA method? I converted a copy of my original working file (just the aligned raw images, no other adjustments) to 32 bit, and set all 30 frames to Linear Dodge Add. The results were far noisier than the mean/median approach, and I seem to be having problems tuning the exposure/levels.

Thanks.


Here are my results, using the various methods I know.

1. The original method I used to use was something I found years ago on a basic astro photography stating tutorial. I used this to a degree in my original post, I call it the gradient ramp method, where you successively increase opacity of each layer from the top to the bottom of the layers list. It is simple, moderately effective, but breaks down when you start to tweak the results with adjustment layers and whatnot.

2. The 32-bit float (HDR) LDA (Linear Dodge Add). First time I've tried this with 32-bit. With 16-bit, you can't stack too many frames before the whole image just becomes white. As such, you can't really remove a lot of noise. Seems moving to 32-bit improves your options...but I may be doing something wrong, as the results (without any other tweaks) seem to be the worst of the three.

3. The median method, where you stack into a smart object then set the stacking mode to Median or Mean. PHENOMENAL noise reduction, especially when you stack a lot of frames. It can almost entirely eliminate noise. Your editing latitude goes through the roof. If you stack too many frames into a smart object, you'll start to lose color fidelity (in the example below, all 30 frames were stacked in one smart object, vs. my original post, where I created batches that were stacked then gradient ramped.)



Original Light Frame (1 frame to show noise):


Gradient Ramp Method (30 frames):


Linear Dodge Add Method (30 frames):


Median/Mean Method (30 frames):


I tweaked the above 30-frame stacks using the LDA and Mean methods. Assuming I did the LDA method correctly, once I started dropping on adjustment layers, there was a marked difference in editing latitude between LDA and Mean. Mean had far more before noise started to exhibit. It was more forgiving and flexible, allowing fine tuning to tighter ranges of tones, without resulting in harsh gradients or transitions. I was able to maintain the black point better with Median than LDA (which ended up a little more red, but pushing it too far resulted in more noise.) Median preserved more subtle and dimmer tones in the outer regions of the nebula, where as LDA clipped more of the outer regions to the noise floor.

 (Again, this is assuming I used the LDA method correctly):

Fine Tuned LDA:


Fine Tuned Median:

[jrista]

Tried another stack tonight. This time, I used an 840mm f/5.6 lens to capture 50x0.6s shots at ISO 4000. Stacked them in a hybrid manner:

• Align in Photoshop (difference method)
• Convert batches of 10 layers into Smart Objects (5x smart objects total)
• Set Stacking Mode for each smart object to Median
• Set blending mode for top 4 smart objects to Linear Dodge Add
• Ramped the opacity for each smart object: 100%, 85%, 70%, 55%, 40%
• Applied adjustment layers to bring out dust detail, tweak color, etc.
• Flattened, unsharp masked, cropped, resized, exported.

Stacking 10 frames into smart objects with median blending resulted in amazingly low noise. Tweaking color and whatnot brought some of that noise back out, but it was still far lower than I've ever had with non-tracked deep sky astro before.

[Rienzphotoz]

Tried another stack tonight. This time, I used an 840mm f/5.6 lens to capture 50x0.6s shots at ISO 4000. Stacked them in a hybrid manner:

• Align in Photoshop (difference method)
• Convert batches of 10 layers into Smart Objects (5x smart objects total)
• Set Stacking Mode for each smart object to Median
• Set blending mode for top 4 smart objects to Linear Dodge Add
• Ramped the opacity for each smart object: 100%, 85%, 70%, 55%, 40%
• Applied adjustment layers to bring out dust detail, tweak color, etc.
• Flattened, unsharp masked, cropped, resized, exported.

Stacking 10 frames into smart objects with median blending resulted in amazingly low noise. Tweaking color and whatnot brought some of that noise back out, but it was still far lower than I've ever had with non-tracked deep sky astro before.

AWESOME! ... I've never tried Astrophotography before, but your images have given me lots of inspiration ... I plan on trying it within the next 2 or 3 weeks during my vacation and will also try out your editing method. Thanks for sharing.

[jrista]

Tried another stack tonight. This time, I used an 840mm f/5.6 lens to capture 50x0.6s shots at ISO 4000. Stacked them in a hybrid manner:

• Align in Photoshop (difference method)
• Convert batches of 10 layers into Smart Objects (5x smart objects total)
• Set Stacking Mode for each smart object to Median
• Set blending mode for top 4 smart objects to Linear Dodge Add
• Ramped the opacity for each smart object: 100%, 85%, 70%, 55%, 40%
• Applied adjustment layers to bring out dust detail, tweak color, etc.
• Flattened, unsharp masked, cropped, resized, exported.

Stacking 10 frames into smart objects with median blending resulted in amazingly low noise. Tweaking color and whatnot brought some of that noise back out, but it was still far lower than I've ever had with non-tracked deep sky astro before.

AWESOME! ... I've never tried Astrophotography before, but your images have given me lots of inspiration ... I plan on trying it within the next 2 or 3 weeks during my vacation and will also try out your editing method. Thanks for sharing.

It is really fun! Without a tracking mount, it is a holy hell of a LOT of work, though. The technique I used above is the only one that actually made non-tracking deep sky astrophotography worth it for me, as it actually brings out some detail from images that almost look entirely black before processing...but it takes a LOT of images.

I purchased a really basic Newtonian reflector with simple motorized R.A. tracking. It isn't perfect, and over time there is still drift in declination, but I am hoping, assuming I can get it polar aligned right and figure out the correct slew speed, that it will get me some better light frames to work with, and lighten my workload. (Ironically, it doesn't even gather as much light as my 600mm f/4 lens!! The telescope has a 114mm aperture, where as the 600/4 has a 150mm aperture. The real benefit of the telescope is its tracking...hopefully I can figure it out and get it working right. Well, either way...I'll be posting something here soon enough. Maybe I'll be able to get the horse head nebula!! )

[jrista]

Did some more astrophotography last night. Worked on some wide field stuff, using my 100mm f/2.8 macro lens. Managed to get some decent results with stacking, but the 7D's low SNR is really killing me. Here is the axis of nebula in Orion:



From the bottom, you have M42 (Orion Nebula), M43 (De Mairan's Nebula), IC434 (Emission Nebula behind Horse Head), NGC 2024 (Flame Nebula) and M78 (follow the axis of orion, horse head, and flame nebulas up near the top edge, small smudge is a reflection nebula.) This is a stack of 30 frames, each 8 seconds long, ISO 3200.

(NOTE: The noise of the 7D, even after median stacking, is simply too great to eliminate with such short exposures and low signal. I pushed the exposure around as much as I could without making the noise overly apparent, but blah...if you see a lot of it, your screen is to bright!! Hope a 5D III (or better, a decent telescope and a peltier-cooled CCD astro camera) finds it's way into my hands sometime in the near future. )

[scyrene]

I dunno if my experience is relevant, but I held out for as long as I could before I got a tracking mount. You can do good stuff with short exposures if you go through the proper motions of dark and flat frames, and stacking a lot. Dark skies/astro filters probably make the most difference beyond that. I do all my aligning and stacking by hand in Gimp (I'm not sure any of the good free astro stack/align software is available for Macs, but anyhow that's what I'm used to now). Having said that, a tracking mount can push things further than anything. Exposure times of tens of seconds up to minutes can be transformative.

[jrista]

Reprocessed a few times with DeepSkyStacker. Tweaking the final result is a real PITA, but when you figure out how to do it right, the results are much better:

I dunno if my experience is relevant, but I held out for as long as I could before I got a tracking mount. You can do good stuff with short exposures if you go through the proper motions of dark and flat frames, and stacking a lot. Dark skies/astro filters probably make the most difference beyond that. I do all my aligning and stacking by hand in Gimp (I'm not sure any of the good free astro stack/align software is available for Macs, but anyhow that's what I'm used to now). Having said that, a tracking mount can push things further than anything.

You can extract a certain degree of quality from non-tracked stacking, but there is a limit. With short exposures, you have a very low signal strength. While you can improve SNR with stacking, you can't improve the actual image signal strength beyond a certain point, so you can never get the nice fine detail that a long exposure gets you. I've spent about two months now trying...and the shot above is about as good as I think I'll be able to do without tracking (or exceptionally dark skies, which are really rare and hard to find.)

I have done a fair amount of manual stacking in Photoshop, and the results can be quite good. Stacking software, especially the more complicated versions like DSS, Nebulosity, etc. are much more capable, but they have a high learning curve, and often their toolsets are difficult to use. I have avoided DSS up till now, but I just spent the bulk of the day working on the shot above, and I think I finally have it figured out. It's a bit noisy (it got much too cold last night, and I packed it in before I took dark frames and bias frames), but that can easily be delt with.

Exposure times of tens of seconds up to minutes can be transformative.

Indeed! I can't wait to get my hands on the Celestron EdgeHD 11" CGEM DX. I had my eyes on a 5D III for my next photography, but I think I'm going to move the telescope to the top of my list. I am curious to see how the 7D II turns out, and for astrophotography, no DSLR will really do what I want, so I'm planning on getting a monochrome CCD with the biggest pixels I can find (probably around 9µm to 9.5µm, or perhaps 5µm with the option to 2x2 bin) an dual-stage peltier cooling (which gets you up to around 77% Q.E.) I'll then be able to filter Ha, Hb, Luma, R, G, B, and any other bands independently, and blend them in post for very high detailed, full-color wide band images.