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  #1  
Old 14-06-2018, 02:30 PM
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Jsmitt94 (Jacob)
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ZWO ASI1600MM pro gain

Hi all,

was just after what gain people who own this camera use when shooting in NB to give them optimal results?

I'm using a SW ED80 BD and am purchasing a GSO RC6 in the next day.

Any information would help!

cheers.

Jacob
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  #2  
Old 14-06-2018, 03:23 PM
glend (Glen)
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Most of my narrowband is shot at Unity (Gain 139, Offset 20) and I tend to use 300sec subs.
Have a look at Ray's (Shiraz) exposure charts for the 1600, there is one for LRGB and one for narrowband.
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  #3  
Old 14-06-2018, 03:59 PM
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Quote:
Originally Posted by glend View Post
Most of my narrowband is shot at Unity (Gain 139, Offset 20) and I tend to use 300sec subs.
Have a look at Ray's (Shiraz) exposure charts for the 1600, there is one for LRGB and one for narrowband.
There is no option for offset anymore for the 1600, so how do I judge unity gain?
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Old 14-06-2018, 04:15 PM
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Quote:
Originally Posted by Jsmitt94 View Post
There is no option for offset anymore for the 1600, so how do I judge unity gain?
Gain 139 is still gain 139 i believe.
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  #5  
Old 14-06-2018, 07:22 PM
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The offset now defaults to 50 at all gains.
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  #6  
Old 14-06-2018, 08:19 PM
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Originally Posted by kens View Post
The offset now defaults to 50 at all gains.
Anyone know why zwo took away the option to adjust?
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Old 14-06-2018, 08:46 PM
kens (Ken)
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Mainly for simplicity. Not all applications enable offset to be adjusted. And having too low an offset is not good. The only possible downside to having a fixed offset is that it reduces dynamic range at low gain. On the ASI1600 the loss of dynamic range with offset 50 at gain 0 is negligible
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Old 14-06-2018, 09:14 PM
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Originally Posted by kens View Post
Mainly for simplicity. Not all applications enable offset to be adjusted. And having too low an offset is not good. The only possible downside to having a fixed offset is that it reduces dynamic range at low gain. On the ASI1600 the loss of dynamic range with offset 50 at gain 0 is negligible
Thatís strange, I was shooting at 79 gain and mistakenly had offset at 21 (normally 12) a few weeks ago and I saw a significant difference in the range.....or maybe I was imagining it?
It is a OSC though so maybe that makes a difference?
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  #9  
Old 14-06-2018, 09:51 PM
glend (Glen)
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Jon Rista has done a lot of research on various 1600 setting and how to configure for high gain narrowband, etc. His CN threads related to the 1600 are worth reading.

I had also heard that ZWO locked Offset, in the later Pro models, because it seemed to be confusing owners, who might be searching for an optimal setup for particular conditions. Happily my Version 1 1600 allows full control, and certainly most software still supports selective Offset.
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  #10  
Old 14-06-2018, 10:41 PM
kens (Ken)
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Quote:
Originally Posted by Imme View Post
Thatís strange, I was shooting at 79 gain and mistakenly had offset at 21 (normally 12) a few weeks ago and I saw a significant difference in the range.....or maybe I was imagining it?
It is a OSC though so maybe that makes a difference?
How did you assess the dynamic range? The normal way is FWC/read noise
In 12 bit terms at offset 12 and gain 79 (2e-/ADU) it would be 4084/1.1=3712 or 11.858 stops. With offset 21 it becomes 4075/1.1=3704 or 11.855 stops.
You'd have to do a side by side comparison on the same night. For instance, the moon could make a significant difference.
Your mistake in setting the offset is a good reason for it being fixed now. If you set too offset too low you risk clipping to black.
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  #11  
Old 15-06-2018, 06:03 AM
Imme (Jon)
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Quote:
Originally Posted by kens View Post
How did you assess the dynamic range? The normal way is FWC/read noise
In 12 bit terms at offset 12 and gain 79 (2e-/ADU) it would be 4084/1.1=3712 or 11.858 stops. With offset 21 it becomes 4075/1.1=3704 or 11.855 stops.
You'd have to do a side by side comparison on the same night. For instance, the moon could make a significant difference.
Your mistake in setting the offset is a good reason for it being fixed now. If you set too offset too low you risk clipping to black.
I must admit those numbers are not my own, pulled from reasearching and reading various threads across the internet.....and they seemed to work well on an F5 newt with 2-3 min exposures in a fairly dark sky.
I’ve now moved to an f7 refractor and have found unity gain to be a good setting with 3 min exposures.....but still testing that theory!

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