Inconsistent gain range on ZWO cameras

ZWO ASI2600MC Pro ZWO ASIAIR Plus CMOS Acquisition Deep Sky
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AstroRBA avatar
AstroRBA avatar
This has nagged me for some time:

Example; the ZWO spec sheet graph for the ASI2600MC shows a 0 to 450 gain range (with HCG occurring at value 100) but then their *own* ZWO ASI Air on board setting menu presents a 0 to 300 gain range !!?? I wonder if HCG is still 100 in that case?

Not just the 2600, I have several other ZWO's and all are represented differently within ZWO's OWN world.

And then Sharpcap also presents a totally different range. 

I mostly watch histogram values in any case but the above has always bugged me!

I'm sure that there's a simple answer to this?

Thanks!
noon avatar
noon avatar
I have noticed the ASIAIR Pro often cuffs the cameras a bit more than their spec (and ASCOM) drivers allow. Similarly it just kind of takes care of offset without giving you the option to choose. I am hypothesizing when I presume they are restricting the settings on the ASIAIR systems in order to reduce the number of variables for the average beginning astrophotographer and increase the likelihood of success. 

I believe you can trust the published HCG. I have not seen anything that shows that it varies in any way. When I look at the FITS data of frames taken with the same camera via ASIAIR vs NINA/ASCOM the e-/ADU is the same for a given gain.

Personally I started off with the ASIAIR when I started astrophotography. It was a good gateway drug: the learning curve was acceptable, all the ZWO hardware played together nicely, and there were few variables that I had to adjust to. As I have gotten more experienced (some may say addicted), I have moved towards a NUC/NINA/Sharpcap/PHD2/Stellarium setup which, while more complicated, allows me a great deal more granular control over my processes. I will add that the range of gain that ASAIAR permits via the interface is reasonable and allows for a great deal of flexibility. I still have the ASIAIR for a small footprint travel setup.

If you have a reason why you "need" (or want) to use gain 450, then you probably aren't using an ASIAIR. I would probably be hard pressed to find any images on Astrobin shot at that gain… Just about everyone uses gain 0 or unity gain because the benefits of going much higher don't often outweigh the drawbacks… full well at gain 450 is a couple hundred and you lose almost a third of dynamic range.

If you are asking about why there is a disconnect, my personal opinion is that is how ZWO operates. They aren't super transparent about how or why they do everything they do. Most people don't mind because, for the most part, their stuff works fine the majority of the time. You have discovered one such example.

Just my opinion,
Ryan
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