Finding the Optimum Camera ISO / Gain for Astrophotography

Been wondering what's the best ISO / Gain setting to use on your camera for Astrophotography. You're not alone. After years of wondering, I found a great website that helped enormously. In this tutorial I first explain the basics of Signal to Noise Ratio and Dynamic Range, both of which are crucial to understanding how to choose the best ISO / Gain setting. Then I show you how to do a simple test using your camera to find out what the best setting to use is (since every camera is different!)
Here are the important Web Links that are mentioned in the video :
For DSLR users there is test data for a wide range of cameras at ...
www.photonstophotos.net/
Excellent web article on ISO...
petapixel.com/2017/03/22/find...

[@GregK8625]

Your videos a very informative; and I'd just thought i would drop you line to encourage you to continue. I've subscribed!

[@matzad747]

I agree with Gergely

[@samarthvedi4195]

Extremely helpful. Thank you for making this

[@vincejenkins1143]

Excellent! Thank you very much - very useful, both the intro (I'm just starting to look at astro cameras in addition to using DSLR) and the test.

[@jonthatcher3958]

very thorough, thank you

[@cierraarmijo]

This was very helpful thank you!

[@newpilot4370]

Science! I love it. Nicely done, sir.

[@rapideye101]

wow, a lot more people need to watch this video. really concise and easy to follow. there is so much ambiguous and false information out there, because no one really seems to understand fully what they are doing. however, your video is really good and delivers exactly what needs to be known. hope to hear more from your in terms of astrophotography wisdom :D

[@martinsastrophotography]

Thanks so much for your really positive feedback. Much appreciated. Clear Skies!

[@neilberkeley5469]

Excellent video thank you

[@GrahamtheWood1]

Brilliant video Martin. Extremely well explained particularly in an area which is tricky to understand, even for experienced photographers. Many thanks and hope for many more informative videos

[@martinsastrophotography]

Thank you so much for the lovely comment Graham. I really appreciate it.

[@SpectreLX]

Thank you for usefull visual sampled video! I think there are also in need the understading the histogram.

[@RIDERZcouk]

Thanks, very useful

[@guystalnaker5184]

Martin - consistently some of the best Astrophotography vidoes on YT. Thank you. I know exactly how I'd do this with my Nikon D7500 (as you did with your Canon). At present I only own the Asicap application for taking images with my two ZWO cameras (both new to me and as yet unused for photography, as I'm still learning what I must know to transition from a DSLR to these dedicated cameras). How might I mimic this multi-ISO process with an AP application like Asicap? Chose 25 - 50 - 100 - 200 - 400 - 800 on a Gain setting and take single shots? Thanks again.

[@martinsastrophotography]

Thank you Guy. Really appreciate the encouraging feedback. I am not familiar with Asicap, but in general you will need to be able to adjust the gain and the exposure time. See if you can do that from within Asicap, or via the ascom driver settings if using ascom. Clear Skies.

[@AstroRef68]

Wow Excellent explanation I always Struggle to make a choice for iso struggle to understand the difference. I have Canon20dA looks similar what you have on settings .

[@martinsastrophotography]

Thank you. Glad it was helpful!

[@kayasper6081]

Good to hear there is another one around who still uses the Canon 20Da. They must be some 20 year old by now! I am very happy with mine and used it extensively, also for day photography. I guess for long time exposures (between 4 and 9 minutes), ISO 1600 might be it´s sweet spot. What do you think? And what are your longest exposures you have used?

[@AstroRef68]

@@kayasper6081 I have use single exposure so far on my photos with 800 iso As I learned stacking I will try when I get back to Europe because I left my camera there . Another hand I used Canon 1100D and none mod and worked excellent on m42 with stacking photo There I used 1600 iso as you say it worked the best

[@trevorpitt406]

Martin, thanks for the experiment and demonstration of the best ISO for your camera. I saw a presentation years ago that must have been based on the same ideas. Since then, when using a DSLR for astrophotography, I pretty much used ISO 800 for everything, deep sky wise. The interesting bits on the video for me are comparing the histogram for 5x stretch of ISO 100 at 14:23 with the histogram for the correctly exposed ISO 3200, that shows the noise very clearly at 14:54, though I am not sure where this noise originates, read noise possibly. I suspect that if you have similar 5x underexposed ISO 3200 image and stretched it x5 it would be very much more noisy than the stretched image ISO 100 shown here. It’s not that important though as it would mean your object is too dim to image with you system. You would need a bigger telescope or 5x longer exposure times.

[@martinsastrophotography]

Thanks for your comments Trevor. It was a real eye opener when I discovered this approach and tried it for myself. Showed me that I didn’t really understand ISO properly at all and made me re-learn it all in a whole new way! Clear Skies.

[@nihonsuki]

It seems to me that the question we should be asking is, for a given total exposure time, is it better to take a few long exposures at low ISO or many short exposures at high ISO, assuming all the images will be stacked to produce one final image? I took a series of photos of the night sky, varying ISO and exposure time to get the same exposure for each image, and took the number of images needed to get the same total exposure time at each ISO setting. I then stacked the images with minimal processing in Sequator, and applied the same levels and curves adjustments to each stacked image. It was not obvious which image had the least amount of background noise since the character of the noise changed. For example, there was more color noise at higher ISOs but the luminance noise might have been less.

[@martinsastrophotography]

Interesting. The other considerations are satellite trails (though sigma clipping solves that) and how much disk space we use (more with shorter exposures) …oh and saturation of stars is worse with longer exposures as well.

[@oq17]

Hi Martin - This was a very good video. Thank you. I do have a question. If every camera has an optimum ISO value, why doesn't the manufacturer just publish it. Moreover, why is there even the ability change it ? Why doesn't the camera come fixed at the best ISO setting ? Thank you!

[@martinsastrophotography]

Thank you. Very sensible questions there! My video addresses the best ISO/gain for Astrophotography specifically. If doing daytime photography the “optimum” ISO would depend on how much available light there is in the scene and what shutter speed and aperture are desired. This would then automatically answer your second question. For dedicated Astrophotography cameras a gain of 100 is usually best, except where the target is very bright and you need to maximise dynamic range to enable longer (and hence fewer) exposures, in which case a gain of zero might be best. Most Astrophotography cameras use sensors that were designed for DSLR cameras, and so they have a gain control facility inherent to the sensor. This facility is therefore passed on to the user as part of the product. I hope this helps.

[@oq17]

@@martinsastrophotography thank you very much for your thoughtful and thorough reply . I love your channel - keep up the good work. Regards , Rob

[@juanantoniogonzalezsanz3153]

Brilliant. Thanks Martin. Do you know the rutine that Sharpcap offers to determine the best settings for the camera as well? Is it equivalent to this? Is is called "sensor analysis" ...

[@martinsastrophotography]

Hi Juan Antonio. Thanks. Glad you liked it. No, I’m not familiar with the SharpCap routine.

[@suzannebeers6238]

Martin...another great tutorial, thank you!! I'm about to add the ASI2600MM to my imaging, is there a good reference you've found that translates this ISO theory and info into gain for the astro camera settings?

[@martinsastrophotography]

Hi Suzanne. Glad you enjoyed it. Good question. I don’t have a specific reference but I see no reason why you can’t try the same technique to find an optimum gain settings on the ASI2600MM. However, be aware that with a higher gain you will blow out the stars with a shorter exposure than you would with a lower gain. So the best choice of gain is not always based on what gives you the best signal to noise ratio….the nature of what you are imaging can come into play as well. Since it is therefore tricky to know what gain to use from one target to another, I would start with Gain set to 100. If you get the opportunity to repeat an imaging session on a target with a different gain, preferably with no moon in either case, you will learn more about what gain works best. I pretty much use gain 100 all the time on my ASI2600MM Pro.

[@paulwhitton957]

Martin your videos are fantastic. I've been learning about Astrophotography over the past year and by chance I found your channel. You explain complicated subjects so clearly in an easy to follow and understandable fashion. Please keep up the good work. Could you look at the subject of banding on Astro images. I have the Canon 5Ds like yours and at low ISO values I see serious bands appearing when I process my stacked astro images. I started out at ISO 800, then 1600 and now I'm up to 3200 to remove the bands. I shoot up to 4 mins, tracked and guided on my Sky-Watcher Heq5 pro but end up with bands at the lower part of the frame. I use Darks, Flats and Bias frames with Deep Sky Stacker and follow Trevor Jones from Astrobackyard and Peter Zelinka, both giving good advice. Neither have a 5Ds camera. Regards Paul

[@martinsastrophotography]

Thanks so much for your nice comments Paul. Really appreciated. If it’s any consolation I have serious bands right across the middle of the sensor on my Canon EOS 5Ds and they also don’t go away with a full set of Calibration frames! I have never figured out why the calibration doesn’t fix them. Very frustrating. Using a much higher ISO lifts the signal up higher above the bands but clobbers your dynamic Range. I can’t help thinking there’s a better fix. I will look into it and let you know if I solve it.

[@martinsastrophotography]

Apparently banding is a Canon thing specifically. I also read that PixInsight deals with it better than DeepSkyStacker. I only see banding when I curve stretch a lot. You could also try longer exposure times to see what effect it has.

[@mikebeswick3420]

really interesting

[@Jpeglism]

It's a bit tricky but some cameras (especially non-astro cameras) do internal noise reduction to improve their low&high gain performance. But generally, when using the same amount of exposure time, by setting to higher gains would help people to capture smoother details in non-saturated area. This is how the ADC works. My suggestion is to shoot HDR, use a gain higher than unity gain to capture the dark faint details, and use some shorter exposures to capture those bright areas. It won't be extending the exposure time too much due to we don't really need to take long shots on bright areas. In my case I simply use < 20% of capture time on the bright frames.

[@martinsastrophotography]

Thanks for your comment. Some astrophotographers will not be ready to start merging data sets with different gains/exposures to cope with a wide dynamic range in the scene. The Great Orion Nebula is a common target that certainly warrants such techniques...when people are ready for that. The tutorial is a process that helps folks find a good place to start, but of course there are many different tricks and techniques to be experimented with...that's half the fun!

[@robgerety]

Thank you. Is the conclusion applicable to other photography? Is it correct to conclude that 400 or 800 iso is the place to be when shooting a daylight landscape for example? Rather than 100?

[@martinsastrophotography]

Hi Robert. No. Daylight photography is a different story. I would always use the lowest ISO possible for a daylight landscape. The reason for the difference is that in daylight the ‘signal’ is much larger so doesn’t struggle to toggle plenty of bits in the analog to digital conversion. That means that the lowest gain is best because you can set your exposure time and aperture to get plenty of signal in your image, while having the least amount of noise. In Astrophotography the signal is very weak indeed and can struggle to toggle enough bits. Thus if the gain is too low the ‘quantisation noise’ that results becomes significant and the signal to noise ratio can be non-optimal.

[@GalaxyArtMedia]

Nice video Martin. However the comparison from the end is not enough in my opinion to establish the best iso for astrophotography using dslr camera. Best test is using similar exposures that we actualy use in astrophotography from short to long, where the iso values will effect different our images, since at very long exposures the camera will generate also more thermal noise that will be amplified by the high iso, and as you said dynamic range will drop, a short iso value is recommended, like iso 400 or 800 and with a faint target and very short exposure you might get better results with a iso even higher than 800 since the increase in iso will decrease the read noise. This will depend of the camera sensor also. Imaging the night sky will be different comapred with a scene photographed inside the house, and accurate simulations are not easy to make. I started gathering astrophotography data fort a comparison of iso values and results with a dslr camera that i will use in a similar video that i will upload on my KZbin channel. Clear sky Martin, stay safe !

[@martinsastrophotography]

Hi there. Thanks for your feedback. I have seen many approaches and they differ significantly. My video reflects the approach that I found the most compelling, but I am open to alternatives. I look forward to seeing your video. Clear Skies.

[@GalaxyArtMedia]

@@martinsastrophotography Thanks Martin. This tests are indeed time consuming, i did spent a few nights and i still need to go out e to gather more images for the comparison. I am working and gathering material for more videos.

[@QawiemJamil]

I’m not sure if I’m interpreting the results correctly. So I found that ISO1600 looks the best for my camera. For astrophotography, does that mean: 1. If I am ever in a situation where I had to choose between an underexposed 1600 vs a correctly exposed 3200, I should just go with 1600 to preserve dynamic range? 2. Does that also mean that If I could choose between a well exposed ISO200 image with a really long exposre vs a well exposed ISO1600 image with a much shorter exposure, I should still go with the latter? 3. My ISO200 actually looked the worst. Why is that? Where is that noise coming from? Does that mean the SNR of an ISO200 image is actually worst when compared to an ISO1600 image given the same amount of signal (same aperture and shutter speed)?

[@martinsastrophotography]

Thanks for your great questions! Here are my responses: 1. Yes. Use ISO 1600. "Correctly exposed" is a common term in photography but is not really the issue with astrophotography, where you want to maximise signal to noise ratio while preventing saturation (clipping) when you take your individual shots and you achieve your "well exposed" finished product by stretching the data after stacking multiple frames. It is usually the case that your individual frames will look very underexposed before you have processed them. Mine usually look almost entirely black! 2. Stick with ISO1600. Choose your exposure time based on avoiding star trails and avoiding saturation (clipping). Start with 60 seconds if you have a tracker. If you don't have a tracker, start with an exposure time in seconds calculated as 300 divided by the focal length in mm. You can then experiment with longer and shorter exposure times. 3. Having the worst looking signal to noise ratio at a low ISO is initially very counter-intuitive, as we're all used to high ISO being more "grainy" in regular photography. But this is because we are confusing "noise level" with "signal to noise ratio". In regular photography we concentrate on getting a 'good exposure', and when we have lots of light we can do that by using a low ISO (gain) because we have so much signal available. In this case we don't see the noise because we have not applied much amplification (gain). When we then take regular photos in poor lighting conditions, we choose a high ISO to increase the gain so we can still get a good exposure, but in doing so we also amplify the noise a lot too...so much that we see it easily in the image. We are therefore tricked into thinking high ISO = poor Signal to Noise Ratio when in fact high ISO means high gain and therefore visible noise in the image. What the signal to noise ratio is doing as we change ISO is MUCH less obvious. It's determined by the detailed design of the electronic amplifier chain in your sensor, and can vary a lot from one camera to another. The test I demonstrated reveals how the Signal to Noise Ratio varies with ISO in your camera. Armed with this information you can then choose the best balance of signal to noise ratio and dynamic range for your camera for astrophotography. Sorry the response was so long!!! Clear skies.

[@QawiemJamil]

@@martinsastrophotography no apologies needed. The response was perfect! And honestly blew my mind. I totally get it now. I was still looking at the results based on the pre-conceived notions that was informed by conventional photography. Thank you so much! Imaging right now at ISO1600 lol! I had no idea I was chasing something I didn’t need to be - unnecessarily long exposures at lower ISO (at least for my current camera). If I may ask one more question - do you think that I could potentially be benefiting from less thermal noise with shorter exposures? (with some time in between exposure to cool down a bit)

[@martinsastrophotography]

Glad it worked for you too! When I first read an article explaining this I was similarly gobsmacked, but the results of the test prove it is right...they do say the camera never lies...but it sure can fool us!! Regarding your exposure times, I would concentrate on avoiding star trails and saturation, rather than worrying too much about noise. If and when you get hooked on this hobby as bad as I am, you will eventually splash out on a cooled astrophotography camera which lets you run the sensor at -15C, which makes a big difference! I have seen people strap a makeshift heatsink and fan onto the back of their DSLR cameras (flip out screen models only!) to cool their sensor. The other consideration is that with shorter exposures you fill up your hard drive a lot faster and the stacking takes longer too. Do you have a tracking mount of some kind? A tracking mount decouples exposure time from star trail constraints and this changes the game completely. The mount is the most important bit of kit you will ever buy for astrophotography!!!

[@QawiemJamil]

@@martinsastrophotography Too little too late Martin. Astrophotography is all I think about now. I'm using a sky watcher star adventurer, and I'm dreaming of capturing beautiful and deep 5 min, 10 min, exposures, with lots of data, plenty of dynamic range etc. But I never really considered the limitations of my camera, and how to get the best results out of my camera. It's a modified lumix G3 by the way, and i've bought clip-in (in-body) broadband and narrowband filters (i'm under bortle 7). I've been pushing it to 2-mins at ISO200-400 and the results have been disappointing. Right now I have a stack of ISO1600 at 30 secs and based on the single frames, it's looking quite good. Let's see how it 'stacks' up!

[@martinsastrophotography]

@@QawiemJamil Oh well, sounds like you are like me then, too far gone to be rescued and doomed to spending all your hard earned cash on cool Astrophotography kit!!! At least you are not alone! I have used the Star Adventurer and it’s a great portable mount, but I would be reluctant to go beyond 1-2 minutes exposure time with it (unguided). I use the HEQ5 (Rowan belt modded) with PHD2 autoguiding for most of my Astrophotography at the moment. It’s a logical step up from the Star Adventurer. I also switched from a DSLR to a mono cooled Astrophotography camera about 3 years ago and it’s a huge change and a big step forward. I can now do Narrowband imaging when the moon is up to avoid moonlight ‘washout’. Enjoy every incremental change…it’s all about the journey, not the destination :-)

[@johnybaby2]

I always thought high as possible ISO with the most tolerable noise was better as you can have shorter exposures., i.e. save time. But actually lower is better because you can stretch it more. Have I got that right?

[@martinsastrophotography]

Hi John. It's a balancing act and not as simple as that unfortunately, which is why I made this video. Clear Skies.

[@GrowingAnswers]

Don’t forget about color model. Some cameras may not show any noise increase with higher iso, but at higher iso you generally get less color model which is only really pronounced after image stretching for astrophotos. Color model varies greatly from sensor to sensor. The best way to show that is through stretched bias frames and the best way to know how much of it shows up in an astrophoto is just by taking roughly 1 minute exposures at the various iso with either the night sky or a black backdrop. Iso variant Canon cameras usually benefit from 1600-3200 for the best trade off between dynamic rage and minimal color model.

[@martinsastrophotography]

Thanks for your comment. I searched online for "colour model" and found nothing relevant. What is your source for this information?

[@GrowingAnswers]

@@martinsastrophotography I’m somewhat new to the hobby for deep space so I likely spelled that word wrong. It refers to the color noise pattern of the sensor. So aside from the random noise, the color noise is usually somewhat constant. It can often appear as gradients. I would have to search for the source that demonstrated that in particular.

[@martinsastrophotography]

Thanks for clarifying. In my experience with Deep Sky Astrophotography the noise level and dynamic range are more important when choosing iso/gain than colour noise. When there is significant colour noise in my stacked image after curve stretching, I will reduce colour noise using a colour noise reduction filter.

[@SpaceFactsWax]

Thank you for sharing. I got the opportunity to see a rocket launch in 2018. Memorable experience. I uploaded a pretty cool montage of the journey to my page.

[@martinsastrophotography]

Very cool! I have seen a few myself and they are truly awesome!

[@edwinsanchez1167]

Hi Martin! As usual your tutorial videos are very informative and well made!! I do have a question regarding bin and gain on a cmos dedicated camera, I just got an asi183 color and I am struggling a bit as I only used dslr. I see that when I zoom in my images, I can see like a checker board which I dont understand what it is and really how to use it. What settings do you recommend so that I can get a good signal to noise ratio and also how do I avoid those checker backckground. I used a 5 min exp. with gain 115 and bin 2x2 thank you!!!!

[@martinsastrophotography]

Edwin Sanchez Hi there. Binning effectively merges raw pixels resulting in degraded resolution but more light gathered per pixel in the image you get. So if you don’t mind degrading the resolution that’s fine. I never use binning because I want the best possible resolution. I normally shoot relatively wide field objects that fill a large part of the sensor. I have the ASI1600MM Pro which is mono, not colour. Have you tried dithering and then stacking your images? You may find this gets rid of the checker board pattern. Also, do you see the checkerboard pattern on the light frames without calibration, or after calibration/stacking? If the latter, what calibration frames did you use?

[@edwinsanchez1167]

@@martinsastrophotography thanks for reply! As it turns out, and I did not mentioned to you, first, I have not done calibration images yet, I will, literally I just got the camera. I learned that since this are .fit b&w images, i need to debayer and stretch. This will bring out the checker shapes in background and the color. I am learning the hard way as it was easier with dslr. So to your questions, I have not calibrated, stretched or process any if them as if yet. I have 2 hours of light frames that are very dark and when I stretch the have checker background SO, if you think that I need to do this before I had reached out to you😔. I’ll do that and let you know what I find, I do appreciate your input!🤝

[@martinsastrophotography]

Edwin Sanchez Hi again. You should stack your images first, before you do any stretching. Try doing this without any calibration frames at first, then make darks, flats, dark flats and offsets and stack your lights with these frames in DeepSkyStacker. I have published a tutorial on calibration on my channel if you are interested.

[@edwinsanchez1167]

@@martinsastrophotography Oh I am interested, I will see it before I do anything and follow your advice!! Cheers!

[@edwinsanchez1167]

@@martinsastrophotography I was able to follow your process per DSS and it came out descent, thank you for taking time out to help me, if you like to see the image just look in @eyethesky, its the horsehead nebula👍🤝

[@KopLamp]

Hi Martin. Martin here ;-). I am starting an Astronomy related KZbin channel and I was looking for names for my channel. I guess using my first name is not that original ;-) Regards, Martin