Gain, Offset, Read Noise, Exposure time?! Let's clarify

Important disclaimer: what I'm presenting here is my understanding of the matter - it may be extremely simplified and not completely accurate. Please let me know in the comments about any errors I made!
So, I've had tons of requests about optimal exposure time - but first, I want to clarify a bit about gain, offset, dynamic range, read noise, and how they're all linked together - and at the same time, how to choose the "right" values for them (there's no right values, but I'm lazy, so I just choose something that seems like it makes sense!). Hopefully this is helpful!
Dr Robin Glover videos: • Deep Sky Astrophotogra...
And the follow-up: • Choosing the right gai...
#astrophotography

[@SKYST0RY]

On a more serious note, your videos are masterful. I've worked professionally in photography and videography for many years, and every time I watch your videos I learn something. Lots of things. Very good info and very well presented.

[@johnposavatz]

Two years later, and this content is still golden! Thanks for teaching me these concepts - super useful for a new astrophotographer.

[@CuivTheLazyGeek]

Thanks John! Happy to see it's still useful!

[@davidrousseau8066]

As Einstein used to say: "If you cannot explain it simply, you do not understand it well enough yourself". Your explanation is LIMPID :) On behalf of all the noobs : Thank you so much!!!

[@newforestobservatory9322]

The best and clearest explanation of what is going on with these f***ing cameras - thank you so much :)

[@CuivTheLazyGeek]

My pleasure!! Glad it helped!

[@johnmacdougall4545]

"...all about swamping the read noise...". Too funny. Thanks for the informative and fun videos

[@rudycajuso29]

Best explanation I have ever seen. Just makes more sense now. Can't wait for your next video.

[@CuivTheLazyGeek]

That is great to hear - I really wanted to make a video that goes step by step in a logical order through the whole thing, and so I am very happy it seems to be effective.

[@jamesmunoz5786]

This is probably the best video explaining this I’ve ever seen. 👏🏻👏🏻👏🏻👏🏻👏🏻👏🏻👏🏻👏🏻👏🏻 I proudly wear your T-shirt

[@dexmeyer3777]

Thank you so much for explanation and I love the great quality of your videos!

[@cuisleproperties6351]

Hi Cuiv, I find your videos both interesting and entertaining. You’ve got the knack! Congratulations and thank you for your thoughtful and helpful insights.

[@weegieb]

Thank you for explaining this. i was looking at these charts for sometime, not being exactly sure of how to interpret them. Now i can say i understand.

[@aliljenb]

Very well explained. Keep up the good work!

[@siegfriednoet]

Great info and very well explained Quiv 👍🏼👍🏼

[@jeffreybackes4664]

Always learn something when I watch your videos. Thanks!

[@guiemlarch]

Wow! So well explained! Thanks so much for this master class!

[@davidaylsworth8964]

This clears up a lot of question I have about dedicated astro cameras.

[@astrobert1254]

This is a bunch of excellent explanations! Thanks!

[@stephanevrat7178]

Quand les choses sont expliquées clairement, on les comprend facilement ! Merci Cuiv pour tout ce travail très pédagogique, il y a tant à apprendre dans ce domaine !

[@blanejnasveschuk6351]

​TY for this complete, simplified and clear video explanation regarding relationships of component variables to exposure choices for image planning. Really helpful!

[@stevel3o7]

thank you so much for working your way through the camera data and charts in ZWO website; very very helpful.

[@BorealisLite]

This is a definitive work. Thank you.

[@tchallalemou5307]

Thanks for going over this. Looking forward to the next vid. Keep it up!

[@CuivTheLazyGeek]

Thanks!

[@calumcadwallader2127]

I can’t tell you how much I appreciate this and all of your NiNa videos, thank you so much 🙏

[@CuivTheLazyGeek]

Thanks for this feedback! It is extremely encouraging!

[@tedmcgee7896]

I've watched a lot of videos, some are so complex you have to have a doctorate to understand, some are so simple that when you are finished you know less than when you started. As the three bears would say, this is just right. Thanks so much.

[@KingLoopie1]

Just enough explanation to really help me along! Thanks, Cuiv! 👍

[@CuivTheLazyGeek]

Happy to help!

[@salomon1639]

Thank you so much for your well prepared explanation.

[@CuivTheLazyGeek]

You are quite welcome! Glad you liked it.

[@donadams.6679]

Thank you! This was very helpful.

[@EdwardRLyons]

Excellent explanation. Thank you! I'm just starting out with my first astronomical camera (a nice simple, affordable one from Svbony), and this provided just the information I needed to understand unity gain, optimal exposure, etc. Great job!

[@olaf335]

Hi Cuiv, thank you very much for this great video. I finally understand how it works! Looking forward to your next video...

[@CuivTheLazyGeek]

My pleasure! Glad it helped!

[@Codyyyyyyyyyy]

Awesome video Cuiv! This is the best explanation of gain and read noise I've come across on youtube.

[@CuivTheLazyGeek]

Thank you! That was the objective, and I'm glad it seems to be helping a lot of people!

[@psegre]

Thanks for going through all this. To clarify, the Dynamic Range plot is the DR of the sensor, not your image. They are not the same. For example, in my typical dual band images of nebulae, 5 min exposures might give histograms with a main peak from say 250 to 1000 roughly. Now if I quadruple the gain, it’ll be 1000-4000. Note that the DR of my IMAGE hasn’t changed at all, it’s the same. The DR plot you show assumes that your histogram covers the full range of 1-65536, which absolutely never happens in reality. So as long as you don’t saturate pixels, you can crank up the gain and the DR of your image will not change.

[@AntPDC]

A very informative comment, thank you.

[@ColeRees]

I have always wondered what these graphs meant! Thank you SO MUCH! Your videos are so helpful.

[@CuivTheLazyGeek]

My pleasure!

[@NeilCorke]

Thank you for the explanation, best I have seen so far!

[@CuivTheLazyGeek]

My pleasure, glad it helped!

[@PeterClarke55]

Thank you for a logical explanation which I found to be refreshing instead of the usual " I used this value and look at my images.....?" No depth and only the message" Don't question just follow what I am doing". Thank you Kurt.

[@CuivTheLazyGeek]

Thanks for the feedback Peter! I like to understand things, so I like to transmit the relevant information that leads to the conclusion as well, as each person's situation and equipment is different! -Cuiv

[@osirislopez4004]

this video answered sooo many of my questions, thanks so much !

[@CuivTheLazyGeek]

Awesome, and glad this helped!!

[@vasodyss]

Thanks Cuiv, I just bought a 294MM Pro and couldn't get my head around all these values by looking at forum posts. You explained everything perfectly!

[@simonwalsh6804]

This is pure gold.

[@giamas72]

As usual. Great work!!!! Very Happy to have find you on internet :-)

[@CuivTheLazyGeek]

Thank you! Glad you found me ;)

[@philleng480]

Nice one, and thank you. Just moving from DSLR to ASI1600MM so very good explanation. Just got to figure it in APT now.

[@prnzssLuna]

That's probably by far the best video on that topic I've ever seen, thanks for that.

[@CuivTheLazyGeek]

Thank you! Glad it was useful!

[@edarroyo007]

Thanks it really helped me to set my ZWO ASI 1600. Analyzing the noise graph I will be playing with a gain of between 75 and 100, since I am in an area with high light pollution, at least for LRGB. Then I figure that a 100 to 150 gain might be more suitable for narrowband imaging. The other thing is to run a preview for each filter combination of gain, exposure and filter and look at the subs historgram as you suggested on the time exposure video.

[@astrogerard2022]

Great explanation Cuiv. Thanks.

[@CuivTheLazyGeek]

Glad it helped!

[@WiseEyez]

' extremely simplified ' he says : ' ) My head is spinning from all this information, well explained Cuiv, gonna have to come back to this video a couple more times!

[@ldipenti]

Really interesting and well explained. Thank you!!

[@CuivTheLazyGeek]

My pleasure Lucas! Glad it was helpful!

[@1cezet]

As always, another great video!

[@CuivTheLazyGeek]

Thank you!

[@tomsharman3136]

Amazing explanation, very clear. good job!

[@CuivTheLazyGeek]

Thank you! Glad it helped!

[@tycho_escher]

Well presented. Enjoying the videos.

[@CuivTheLazyGeek]

Thank you!

[@starman82]

Well done! you seem to be a natural at making the complex simple to understand.

[@CuivTheLazyGeek]

Thank you! I try :)

[@thomasbardenwerper9365]

Yet another GREAT video Cuiv, THANK YOU!! In particular, I like the level of detail you go into explaining things in lazy "layman's" terms. ;-) I often find other astro video producers don't go into nearly enough depth. I've been a subscriber for a while now, I think you've found the informational "sweet spot" for intermediate astrophotographers which I think most AP-ers fall into. Keep up the great work!

[@CuivTheLazyGeek]

Thanks for that feedback Thomas! I try hard to get the right balance, and it can be really difficult, so this is great feedback!

[@stevengibson9295]

Excellent video! Thank you for posting it. Very helpful! Cheers!

[@CuivTheLazyGeek]

No worries, I'm glad it is helpful! I ha e tons of videos on the topics of noise as well :-) Clear Skies!

[@rishigarrod7227]

Finally I get it. Thank you for this excellent explanation.

[@CuivTheLazyGeek]

I am very, very glad it helped!!

[@CitizenSniiiips]

Thanks Cuiv! Looking forward to watching this :)

[@CuivTheLazyGeek]

Thanks!

[@Kuesu721]

Many thanks for these perfect explanations in simple words! I'm a beginner... and feel much more comfortable now! Kind regards, Markus.

[@CuivTheLazyGeek]

Glad it is useful! Many more videos like this on the channel, feel free to explore ;)

[@patchnovae]

Great video as usual Cuiv! None of this made sense to me until you made it so simple to understand.

[@CuivTheLazyGeek]

Glad it helps! It was so hard for me to understand those concepts as well!

[@Coutinhuuhh]

What a great video. Thanks!!!!

[@andreamarini1680]

thanks for this video. I will try to adjust my next shots paying attention to this explanation. I see i can improve something in my image paying attention to this details. Thanks

[@drfritz142]

Thanks so much. There's a lot to be gained from your videos! :-)

[@suzannebeers6238]

Great explanation! Thank you!!!

[@CuivTheLazyGeek]

Glad it was helpful!

[@brianwalton3016]

I endorse everything being said about the video- Great stuff,well explained and as others have said I,ve watched Richard Glover and listened to a pod cast etc on this subject and have an understanding but this video is like the cement between the bricks. It brings it all together. Keep on building !

[@CuivTheLazyGeek]

Will keep building, thanks for the feedback! There is so much ground to cover, so it's keeping me very busy :)

[@beorn8988]

Thanks for explaining it so well and the "don´t worry too much about it" attitude! That´s very much apprechiated by a beginner, worrying too much about basically everything

[@moemode]

I do miss your videos since you took your break. Hope you come back soon . You're quite the character. 👍

[@MrGp3po]

Thanks. This helps make sense of those graphs for my new ASI294MC Pro.

[@CuivTheLazyGeek]

Happy to help!

[@leelangley3713]

I am very new to imaging with the ZWO 294 MC PRO. what seemed very confusing, and i thought i'm never going to get this,now after watching your videos how you present them in an understanding point of view from you to the viewer makes things much easier to learn. I like the way you point out that you may not be the best or that you may make mistakes and to correct you if you do. To me you are doing everything right,and i know that from following your advice things can only get better for me. These videos are first class, thank you and keep up the good work

[@CuivTheLazyGeek]

Wow - thanks for the comment. It really is one thing I strive for - helping others, especially beginners to astrophotography. This hobby can be so confusing! Soon enough, you'll see that I'm not doing everything right - and then you'll be the one making suggestions :)

[@50sKid]

Thank you, I understand a lot more now

[@CuivTheLazyGeek]

My pleasure, glad it is useful!

[@ChristopherKovacsw0anm]

Thanks, this is well explained. Nice to see you using the asi533.

[@CuivTheLazyGeek]

Glad it's helpful! I hope you'll get great results with the 533!

[@AstroPixUK]

Thx for this. Really easy to understand. Keep up the great content

[@CuivTheLazyGeek]

Glad it was useful! Thanks for the feedback :-)

[@felipemacauliffe1528]

What a master class !!!! Thank you so much for your time and great explanations of these interesting detector concepts. I feel I've obtained a better understanding on gain and offset. All the best, clear skies and shine on from the "Cluster One Observatory" in Chile.

[@CuivTheLazyGeek]

Hi Felipe, glad this was useful! And wow... Chile. Darn, you have some of the best night skies on Earth, I am so jealous!

[@felipemacauliffe1528]

@@CuivTheLazyGeek Thanks for your reply. And yes, southern skies from Chile are just amazing. I work as observing specialist at the European Southern Observatory (ESO) and every time I starred at the night sky from the top of the mountains feels like really getting closer to the sky in every sense. Cheers from Chile!

[@ranjitgovindaraj]

Excellent info👌🏼 Even I wondered why my optimal exposure time was so low but I ended up thinking it was more like minimum exposure which you just confirmed. Thanks Cuiv👍🏼

[@CuivTheLazyGeek]

That's pretty much it! I think we tend to be a bit perfectionist in this hobby, which can really get in the way of enjoyment. But yes, if you don't go overboard while going a bit beyond the optimal exposure time, you should be fine! There's another video in this playlist as well.

[@insightvideo6136]

Very nice presentation and very informative! Subscribed!

[@CuivTheLazyGeek]

Thank you and welcome to the channel!

[@DrReinerHutwelker]

Again a great video, Cuiv. As a beginner I have treated the topics this way so far: As long as there is a wall I don't need a door. Thanks for the many doors in your videos.

[@CuivTheLazyGeek]

Glad that this is helpful! I love revealing hidden doors :)

[@MrGuitar50]

Great job!!

[@johnjames378]

Great explanation. I have watched Robins videos several times (they are very good) in the past, but just wasn't crystal clear for me about all this offset, gain stuff since I used to use a modified Canon DSLR. Now I get it!! Logical step by step and the explanation how it all works always works for me.

[@CuivTheLazyGeek]

Excellent!! DSLRs can be so hard to use for astro (I've been through that) because of the difficulty of taking good dark frames! Good luck & clear skies!

[@jimbob4484]

fantastic video. Very informative. Thank you :-)

[@andreasglasser]

Love your videos!! Soo informative!! Thank you so much :) Instant subscriber :)

[@CuivTheLazyGeek]

Thank you! And welcome to the channel!

[@mdaugher1811]

Excellent. Thanks for sharing.

[@CuivTheLazyGeek]

My pleasure! Glad it's being useful!

[@garyferguson2515]

Thanks very much for explaining ADUs! I've never gotten a decent explanation before. (I'm a total beginner.)

[@CuivTheLazyGeek]

Glad it helped! Good luck with the hobby :)

[@sanjayajha362]

Excellent!

[@dontpresstheredbutton9962]

You’re a fantastic teacher. Thank you (from a noob).

[@stephen2615]

Thanks for creating this video as it cleared things up a lot. I have been looking at the optimal exposure time and wondering how to use it so now I will wait for your video. I have two cameras (one a QHY 163C and a QHY 16200A CFW7 without any filters) and now I see the comparison with the ZWO 1600 and 163C as far as stats go. There is no dramatic change like the 533 so I will be staying mostly with the standard gain and playing with the exposures. Still waiting and waiting and waiting for my filters for the 16200A. Bortle 5 here.

[@CuivTheLazyGeek]

Those are nice cameras! And a very decent Bortle level, you'll be having a lot of fun! You might be disappointed by my very cavalier approach to exposure time - but it's something that works for me! :)

[@ant_hart]

That’s some really helpful info 👍🏼👍🏼

[@CuivTheLazyGeek]

That's the goal, so excellent to hear, thank you so much!

[@iphoneawesome123]

Perfect explanation thank you

[@CuivTheLazyGeek]

Glad it was helpful!

[@T-Bear]

Thank you 🙏

[@andycoutant70]

Best explanation on you tube.

[@CuivTheLazyGeek]

Thank you Andy! Glad it was useful!

[@HeavenlyBackyardAstronomy]

Extremely Beneficial for me. Thank you Cuiv

[@CuivTheLazyGeek]

My pleasure, glad it was useful!

[@jeffreyvictor3678]

Cuiv…wow!! I will need to watch this episode at least ten more times to fully understand most of what you are teaching us!! My question is…as you increase gain (thereby shortening exposure time), aren’t you increasing RN?

[@JeffHorne]

Chic, you are on fire lately, and I absolutely love your videos. For the past 9 months, I’ve watched and read everything I could find about imaging with dedicated astronomy cameras, and in particular, gain/offset and how it all relates to DR and noise. I’ve never understood what I should really be doing with offset until watching this video. Your explanations of everything in this video, actually, resonate with me more than any other explanations I’ve found. So, thank you again! Also, sounds like NINA might benefit from renaming it from “optimal exposure time” to “optimal minimum exposure time”, if it’s truly calculating how much time you need in order to swamp the read noise. Maybe?

[@CuivTheLazyGeek]

Wow, again, I'm just so happy when I read this kind of comment! Thank you! On NINA, you are right, it is indeed calculating a time that is the minimum time that the camera should expose to reliably swamp the read noise. As it is in this sense optimized (e.g. the shortest exposure time that achieves that, as per Dr Glover's videos), it probably should still be named Optimal Exposure Time - but it's good for people to know that they don't need to conform to it exactly! - Cuiv

[@JeffHorne]

Cuiv, Lazy Geek in Japan Cuiv, Lazy Geek in Japan I understand exactly what you mean...I’m guessing that you’re even more of a pedant than I am! 😂 I think the reason that people get confused and think that “optimal exposure time” means “max exposure time” because “optimal” just means “best”, and most people in astrophotography think “best” means “as long as possible without being swamped by light pollution”.

[@lavers_1]

incredible content! you're wicked smart

[@CuivTheLazyGeek]

Thank you!

[@midnightlightning1]

Great video - I also add 1 to the Gain I use based on supplier graphs. In my case QHY600 where their website says Gain 0-55 uses LGC and Gain 55-100 uses HGC :) . I use Gain 57 just to be sure as they don't seem to understand boolean algebra. (I have written to them to get it corrected).

[@quadbot5229]

Just last week I received a 294mc pro, this video was incredibly helpful for understanding the terminology that comes with these astro cams! Quality content again! Keep at it! :)

[@CuivTheLazyGeek]

Thank you - and good to hear this is helpful! The 294MC Pro itself begs to be used at gain 120 (or 121 if you're superstitious like me), and it is extremely sensitive. I hope you'll enjoy it!

[@davidgibbon460]

@@CuivTheLazyGeek is that with HGC on or off

[@icanifuwill]

Thank you Cuiv, filled in alot much appreciated - took early advice develop my AP in broadband first (have ASI294C Pro) good pixel size for both my APO's ( F5 to F7 with reducer). Am learning N.I.N.A, love it over SGP, use Pegasus UPB2 & Focuser 2 etc. ☺️🔭

[@CuivTheLazyGeek]

Glad it helped! That sounds like a killer combo - the ASI294MC Pro is such a good camera if you're not in a super light polluted area! It could give you trouble with flats (I recommend taking flats above the gain "jump", so at 121, or I've personally seen issues). Enjoy NINA and clear skies!

[@squirrelsrus1]

Great video. Thank you.

[@CuivTheLazyGeek]

Thank you! Glad it was useful!

[@moxican7]

If I may, at 31:40, "the camera becomes more sensitive" with lower gain... it doesn't. It will have exactly the same sensitivity, however the quantization error will be less the higher the gain setting goes. Regardless, your efforts are much appreciated Cuiv, great video, keep them coming!!!

[@CuivTheLazyGeek]

Not only you may, but please please do point out such mistakes! Thank you so much!! I am so worried about providing wrong information that comments like yours are really extremely helpful and very very welcome! You are absolutely right - the camera does not become more sensitive, although quantization error will indeed be higher there. In the end the substrates in there never gets more sensitive - it's just how we get the data back that changes everything. Thank you so much!! I will keep going, and please please never hesitate to point out mistakes!

[@skyboy98046]

Thanks for the education!!! 😜

[@ochentaiocho]

Muy bueno! Saludos desde Chile!

[@RaysAstrophotography]

I use mainly HDR with F/2 scopes. Keeps it simple, Great presentation!

[@CuivTheLazyGeek]

Ray?! I love your channel, thanks for dropping by! Awesome job on M51 with that C14 (also, green with envy - even though I know my seeing doesn't justify a C14!). Also F/2 scopes..... :D so good!

[@RaysAstrophotography]

@@CuivTheLazyGeek Thanks Cuiv!

[@geitemans]

Super usefull video! Thanks for explaining this so well and taking your time to do it! Unity gain for my 1600 it is for nebula season, and pleiades and orion will get 75-100 :)

[@CuivTheLazyGeek]

Glad it was helpful! Good luck with your imaging & clear skies!

[@derekregan6926]

Well, that explained it easier than others have, mentioning no names

[@febsat]

Excellent Cuiv. I'm trying to learn as much as possible, before I take the step from DSLR to dedicated astro camera. Your video was like a giant step! Lots to learn and understand. Thank you for making it a little less daunting. Prior to watching, I was of the mind to get an ASI 533 MC PRO or ASI 2600 MC PRO, utilizing a filter drawer, with the Optolong L-extreme. Based on my gear, (WO GT 81 with WO .8 FF/FR), these sensor sizes would work reasonably well. Another question I have relates to ZWO documentation, which states for the ASI 2600 to use either a 0 gain setting or 100 gain setting. The 100 I understand after watching your detailed explanations, however, I don't get why they would say 0 gain. Can you explain that for me? Thanks for running one of the best channels on KZbin!

[@CuivTheLazyGeek]

I think the 0 gain has a marginally higher dynamic range than 100, which is likely the reason!

[@BB-tw1ry]

Great video, btw you could also get the 2600mc pro aps c but its 16bit

[@JeffHorne]

RE: 100 vs 101 gain, I get it. All it takes is one developer somewhere in any of your apps to have coded it as “through 100” vs “to 100”...and it’s an easy mistake for one to make! I’m going to always use 101 gain with my 2600 from now on (it has that same jump at 100 that your 533 does). I’ve thought this ever since you mentioned that you use gain 101, several videos. Thank you! 😊

[@CuivTheLazyGeek]

Hahaha, exactly! I mean I'm sure it's OK at 100 but.... :D How do you like your 2600?

[@JeffHorne]

Cuiv, I love the 2600, but I came directly from a Canon 5DmkII, so I don’t have a good reference/comparison to other cooled/dedicated astro cams. On paper, it’s very similar to your 533, though, as I’m sure you know! 😊

[@paulbarrett423]

that was great, I think where a lot of people (me included) go wrong (especially photographers) is we think of gain as a sort of ISO, which makes it difficult to get your head around then as the lower the ISO the less noise. Using the 1600 if I put my gain at 139 take an image then put my gain at say 30 or 50 the image is a lot less grainy so (in my case i cant speak for anyone else) You cant help then by having that stuck in you head that reducing gain makes for a cleaner image. Hope i make sense.

[@CuivTheLazyGeek]

Glad to hear that! Now there is a very important distinction to make: noise versus signal to noise ratio - for the same total stack time, stacks at different gains show remarkably similar levels of SNR (which is what we are after). So something to keep in mind as well!