Questions about Gain Settings and Offset Control for ASI585MC Air

paulitoweb

Dear @Tech@ZWO,

I recently purchased an ASI585MC Air and am currently waiting to receive it. In the meantime, I've been studying the camera’s gain settings and I have a few concerns I’d like to clarify.

Specifically, I noticed that at the HCG (High Conversion Gain) value of 252, the Full Well Capacity is slightly below 2ke⁻. This worries me a bit, as I fear it may limit exposure times to avoid star saturation. On the other hand, using a lower gain, such as 50, results in a much higher Full Well Capacity (over 20ke⁻) and dynamic range, but with a significantly higher readout noise of around 5.5 e⁻ RMS.

How should I approach gain selection for deep-sky imaging with this camera? Are there any recommended exposure times based on gain values and their corresponding readout noise?

Before making the purchase, I was very excited about the ASI585MC Air, but after carefully analyzing the gain charts, I’m now a bit concerned about optimizing the settings for best results.

Lastly, may I suggest adding the ability to manually set the offset value from within ASIAIR? It’s such an important parameter, and including it—even in an advanced settings section—would be very helpful, even for users who rely on the simplified 1-2-3 setup process.

Thank you in advance for your help and support. I’m looking forward to your reply.

Best regards,
Paolo

Kevin_A

Yeah, this is a tricky camera I have found. I have been limiting my use of gain252 to 60-90s exposures for broadband imaging using a uvir cut filter and 180s for dualband filters. I use this gain strictly for dim targets like small galaxies. For brighter targets I opt for gains of 100 to 150 and I can bump the exposures up to 120 for broadband and 240-300s for dualband imaging. This reduces to star over-saturation to an acceptable level but clipping will always be an issue unless ZWO eventually decides to drop HCG to around gain 150-182 allowing a more reasonable full well capacity. It is the achilles heel of this good sensor… the way it has been implemented.

4H29wipq

Yes it is purely a ZWO choice. Other brands allow you to switch the HCG on/off at your desired gain.

The gain settings depend a bit on the object and your light pollution levels. I also don't like the high readout noise at lower gains, but have gotten goed results with long subs like 5min.

In asiair you can't set the offset, but you can in the asistudio. I found an offset of 8-12 at gain 252 works best to save most of the histogram. At gain 100, 5 would do the trick.

Tech@ZWO

Thank you very much for your guys suggestions, we noticed some similar feedback on 585, and are considering how to optimize that.