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First light with my ASI533 OSC - what gain/offset?

Astrophotography Beginner CMOS DSO Equipment Imaging
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#1 PhotonHunter1

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Posted 13 March 2021 - 05:46 PM

Going out tonight with my ASI533 OSC and wondering the best gain/offset to use without a filter, and with my L-Extreme filter.

 

Thanks!


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#2 nyx

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Posted 13 March 2021 - 06:08 PM

Try Gain 101 and Offset 5.

Edit: these are the values suggested by SharpCap Pro when I use the Smart Histogram in order to determine "ideal" exposure time. Gain 100 is the Unity Gain according to ZWO, so 101 "guarantees" you are at unity gain.

Edited by nyx, 13 March 2021 - 06:16 PM.

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#3 bobzeq25

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Posted 13 March 2021 - 06:09 PM

I'd use gain 100 and offset 10, offset 5 is probably fine.


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#4 wxcloud

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Posted 13 March 2021 - 07:47 PM

Been using 101 with 70 offset. Not sure where I got 70 as an offset, maybe I should knock it down a bit?
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#5 AhBok

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Posted 13 March 2021 - 11:38 PM

I use gain 100 and offset of 40. As mentioned a lower offset is fine for gain 100. The reason for some using an offset of 70 is the ASCOM driver defaults to it. The reason I use an offset of 40 is simple. 40 gives me headroom on the left side of the histogram at all possible gain settings I use. I formerly used an offset of 10 which is fine for gain 100 and below and for some amount higher than 100. At gain 300, which I use rarely, an offset of 40 gets the black point at short exposures off the left side of the histogram.

Again, at unity gain (100) almost any offset is fine so pick a number between 5-70. You will not see the difference in your images.
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#6 bobzeq25

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Posted 13 March 2021 - 11:39 PM

Been using 101 with 70 offset. Not sure where I got 70 as an offset, maybe I should knock it down a bit?

Almost certainly.

 

It helps to know what offset is for.  You want to add a bit to each pixel so that noise never drives the signal negative.

 

Typically a 16 bit average ADU of about 500 is plenty.  If yours is much more than that (I believe so), you should reduce offset.  Note that 500 is not some ideal number, it's just a ballpark to be in.  <smile>


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#7 PhotonHunter1

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Posted 14 March 2021 - 12:12 PM

Thanks everyone - very helpful information!


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