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Old 16-09-2016, 05:42 PM
spiezzy
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A Question about Gain with a ASI 1600mc

hi to all
I have a ASI 1600mc one shot colour and use Nebulosity to capture works great but I am a little unsure on how to use the gain setting and what Unity Gain is I have a screen shot of of Nebulosity 4 it is in simulator mode but this is what it looks like with the ASI connected with the Gain and Off set .
you can see with the gain there are 2 numbers 1 for percentage value and 1 for a setting value when you adjust the setting value the percentage adjust
what setting should I be looking at or percentage value .
when people talk about unity Gain they mention setting of 120 for example
any help would be much appreciated .
sorry if it sounds like a dumb question but it just is not gelling
cheers Pete
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Old 16-09-2016, 07:15 PM
glend (Glen)
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Pete i suggest you read through some of the Cloudy Nights forum threads, the the Beginner and Intermeadiate Imaging sub-forum, on the ASI1600, and the topic covers both the colour and mono versions.
Gain in the ASI1600 can be thought of like ISO is to DSLRs. Offset is like brightness.
There is a sweet spot for Gain at 75 where you get maximum pixel well depth. Unity Gain is a Gain setting of 139, and an Offset of 20, and represents a good starting point for people new to the camera.
I do not use Nebulosity so i can't comment on your pic, i prefer SGP.
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Old 16-09-2016, 07:36 PM
spiezzy
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Thank you so much for your reply Glen I will do as you suggest .
I understand what you mean by the sweet spot of 75 but that is what is confusing me as with Nebulosity do I take the gain up to 75% which will make
my setting value 48 or if I take the setting value up to 75 that will make the percentage value around 115%.
I am thinking I should just be using the percentage value and set that at 75%
but I will get onto Cloudy Nights and have a bo peep
cheers Pete
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Old 16-09-2016, 08:26 PM
glend (Glen)
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Look i don't know what Nebulosity is up to, but you can set the gain and offset in the camera ASCOM driver.
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Old 16-09-2016, 09:43 PM
spiezzy
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no worries Glen
I had a look at Cloudy Nights and there is a lot of info there mainly on the mono but still good info thanks for the tip .
also I had a pm from a top bloke who has the same set up basically as my self and he has set it straight for me basically you ignore the percentage value and just use the setting value easy as and all sorted
thanks again for your help much appreciated
cheers Pete
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Old 16-09-2016, 11:37 PM
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Yeah, the CN forum, esp Jon Rista, is very useful for this cam. Latest opinion and image evidence is that gain 200 is the best compromise, can't wait to try this setting, rather sensitive. Have fun!
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Old 17-09-2016, 04:56 AM
glend (Glen)
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Quote:
Originally Posted by SimmoW View Post
Yeah, the CN forum, esp Jon Rista, is very useful for this cam. Latest opinion and image evidence is that gain 200 is the best compromise, can't wait to try this setting, rather sensitive. Have fun!
Well not exactly. What Jon Rista and some others are doing is experimenting with high gain settings for narrowband in order to produce 'fast narrowband' subs in usually light polluted areas, where people don't have time to use setting that would build deeper images; or where short subs are easier to acquire and do not require guiding in some well aligned cases. Shooting at Gain 200 is going to cost you depth, the well depth is no where near what it is at Gain 75. However, it does give you passable images fairly quickly, and were talking about 90 sec subs for narrowband, which is unheard of with other cameras. This is not something to try with broadband, LRGB.
And it is not recommended for the OSC versions unless they are shooting through narrowband filters.
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Old 17-09-2016, 07:51 AM
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Atmos (Colin)
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I agree with Glen. Just did a quick calculation and the ASI1600 mono up at my dark site would take about 150s (gain 0) to become sky limited, the same time as my QHY22. The ASI has a lower read noise but the QHY has larger pixels and a higher QE.

At gain 200 that drops down to 20s but you lose a LOT of dynamic range in the process.
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Old 17-09-2016, 05:10 PM
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I understand the rationale for imaging at gain=75 and I'll some experiments if it ever stops raining but I suspect most of my "conventional" imaging will be done at unity gain=139. Of course, part of the fun of the 1600 is supposed to be the "unconventional"...but any gain value below 75 is essentially throwing photons away, and in the astro game that just doesn't make sense to me...

Oh and Pete much of the information on the 1600 mono is relevant to you with the colour, as a rough rule of thumb try multiplying any exposure times quoted for luminance with the mono by 3 and you'll be in the ballpark for your colour. More importantly IMO is to check you are adequately exposing on any given night/location. It might not require exposures as long as you might think...I'd expect about 2 or 3 minutes of exposure (in a conventional fashion) would get you pretty close, depending on how dark your imaging site is.
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Old 17-09-2016, 07:13 PM
spiezzy
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Thanks Dunk
that is a great formula to work to much appreciated
cheers pete
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Old 18-09-2016, 07:30 AM
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Slawomir (Suavi)
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Quote:
Originally Posted by glend View Post
Shooting at Gain 200 is going to cost you depth, the well depth is no where near what it is at Gain 75. However, it does give you passable images fairly quickly, and were talking about 90 sec subs for narrowband, which is unheard of with other cameras.
This may not be entirely true, at least for brighter objects and for Sony sensors. Here is my attempt at 120s subs from two years ago from near Brisbane's CBD; I reckon I could easily get away with much shorter 3nm subs on this target: http://www.astrobin.com/141089/F/

And of course narrowband subs could be even shorter (but not optimal) on a faster scope and with less arcseconds per pixel
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