Gain settings people have success with when shooting LRGB - Forums

Topic starter

Jul 31, 2022

Hi all,

I've had a ASI1600 for about a year now and have been largely shooting narrowband so far (due to the weather and full moon making clear nights with no moon hard to come by). I have been using the unity gain settings of 139 and seem to have found my sweet spot for exposure lengths. I'm now looking to get more LRGB time on the camera and have shot with a gain of 139 and 40 secs for L and 60 secs for RGB. I am in a bortle 6 zone and I know I am likely hitting the full well limits and my ADU's for sub are up in the 1000's.

Really curious about what others with this camera use for gain settings when shooting LRGB.

Engaging

Andy Wray

Jul 31, 2022 · Edited: Jul 31, 2022

I'm in a Bortle 5 zone and shoot 90 secs for RGB and 30 secs for Lum both at gain 139. My median ADU for subs is around 3,500. I typically can only just see a few (less than half a dozen) stars on the unstretched sub, so the vast majority of stars are unsaturated.

Well Written Concise

Torben van Hees

Jul 31, 2022

When I had the camera I switched to gain 79 for narrowband and gain 0 for broadband in Bortle 6, to be able to expose longer without blowing out stars.

DerPit

Jul 31, 2022

I tried using gain 0 to increase actual full well. At least my unit of the 1600MM does show banding issues at that setting, so I've switched to 76 (about 'dual') with good results (IMO).
For exposure times I've always looked at the number of saturated pixels/stars, trying to keep the px number below ~400. For me that led to exposure times usually between 20 and 90 seconds for RGB (I hardly ever use L)

Frank Conte

Jul 31, 2022

The best images with my 1600 in narrowband came with Gain 120 offset 10 @180 sec exposure. I'm in a Bortle 5 area.

Philipp Weber

Jul 31, 2022

Technically speaking, the thing which matters is that the read noise, which is a parameter depending on the gain, and the exposure time of each subframe somehow make sense together. There are rather long elaborations on this topic on the internet and other literature.
The other thing is that of course the full well is reduced with higher gain and things like stars are blown out rather quickly.
I'd make this bold claim: As long as the stars or even the object in question are not blown out, for the vast majority of people under average-ish skies doing broadband imaging at any gain should be just fine. But something in the lower half will probably be more reasonable to avoid said issues of overexposure.
Personally I usually do 120 for broadband imaging with 180s subs, and sometimes 200 for narrowband.

Andrej Karlic

Jul 31, 2022

I used to do it with one take and sacrificed stars for the richness of object I was imaging. But now I do it in a bit different aproach on my new images. I usually do my LRGB subs with gain 139 for extracting dim parts of objects and ignoring the stars. And then do another run with lower gain just for the stars. Both blend in software and regain both the object and more balanced color in stars.

P.s. You can do this approach for your already done images. Just image stars for same field and blend with old pictures. This way you get better star colors without sacrificing anything.

Astrosatch

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Olivier Ravayrol

Jul 31, 2022

Hi,
A good return experiences read on forums about this camera :

Optimal SNR: Gain 75/Offset 15, 480-600s
Balanced SNR/Resolution: Gain 139/Offset 30, 210s
High Detail/Resolution: Gain 200/Offset 60, 90s..."

Personnaly, after tests, I use the first one configuration and so 360/420s exposure for narrow band and 240/300s for LRGB.
(As I live in a Bortle 5 zone, I prefer using CLS filter against L filter for lunimance)

urmymuse

Jul 31, 2022

Hi,

I use Gain 139 Offset 21 and expose for 30 seconds - I am in Bortle 7/8 zone

Cheers

urmymuse

Mark Eby

Jul 31, 2022

I image in a Blue zone and for LRGB use the following with F5 - F7 scopes:
L: 2 mins, gain = 139
R: 2 mins, gain = 200
G: 2 mins, gain = 200
B: 2 mins, gain = 200

I know this seems like too much gain, but it gives great S/N ration and does not cause that much more star bloat.

Cheers,
Mark

qcernie

Aug 1, 2022 · Edited: Aug 1, 2022

Bortle 2 zone. I use 139 gain at 120 secs. for LRGB and 300 gain at 300 secs. for narrowband.

Ernie

Josh Jones

Aug 1, 2022

I am in bortle 3-4 and shoot F/2 RASA 11 and 1600mm and LRGB I have good luck with gain 75 and 139 and short 10, 15, 30 second images depending on target. Narrowband I go 139 and usually 180, 240, 300, sometimes 600s exposures depending on target.

David Wright

Aug 2, 2022

Hi Chris, I'm in Bortle 5/6 and have not had a lot of time on LRGB targets - bad weather with my only clear skies coinciding with fullish moons. So been limited to narrow band. Typically I'm using 30 to 60 second exposures on Ha, Oiii and Sii. Any more than that and I lose definition and colour in the stars. Always shooting at unity gain (139) and -10 degrees. Keeps my dark library reasonably manageable…..

Clear skies!

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Andrej Karlic

Aug 2, 2022 · Edited: Aug 2, 2022

David Wright:
Hi Chris, I'm in Bortle 5/6 and have not had a lot of time on LRGB targets - bad weather with my only clear skies coinciding with fullish moons. So been limited to narrow band. Typically I'm using 30 to 60 second exposures on Ha, Oiii and Sii. Any more than that and I lose definition and colour in the stars. Always shooting at unity gain (139) and -10 degrees. Keeps my dark library reasonably manageable.....

Clear skies!

*** Hi, David.
I don't understand how can you lose dynamic range with such short exposures. I usually image NB at gain 139 or 200 and from 300-600s. Yes the brightest and a bit less bright stars are clipping but this never prevents me from getting the most from object I'm imaging. It also depends from bandwidth of filters and aperture of telescope. I can do stars later with much shorter exposures for better results. Besides NB filters are not very star color friendly. Best to use RGB filters for that.

Andrej

***

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Molly Wakeling

Aug 3, 2022

I always use unity gain, for all filters and all Bortle zones, which is 139 for the 1600MM. At unity gain, 1 electron = 1 ADU (analog-digital unit; essentially, a step in the brightness level of the digital image) (approx). Less than unity gain, and it takes multiple electrons to step 1 ADU (which increases your dynamic range; this can be helpful for very bright targes with dim stuff too like Orion, but I still don't use it for that). More than unity gain, and you're "splitting" electrons, having more brightness levels than you need (causing reduced dynamic range).

I typically shoot 3-5 minutes LRGB (3m on my f/5 scope, 5m on my f/7 or f/10 scope) and 5 or 10 minutes narrowband (5m on my f/5 scope, 10m on my f/7 or f/10). With CMOS, I could probably use shorter exposure times and take more subs – it's on my list of things to test.

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Rudi Bjørn Rasmussen

Aug 31, 2022 · Edited: Aug 31, 2022

Bortle 3, unity gain (139) and 120 sec exposure times on L, R, G and B with a 10" f/5 ATM newton