How to add the gain & offset to fits headers


how to add the gain & offset value in to fits headers when i using SGP, I am using my qhy9m with ascom driver

I don’t believe these properties are exposed by the ASCOM interface so we wouldn’t be able to populate them.

What benefit does the gain and offset in the FITs header provide you? Generally these values are fairly static.


The CameraV2 interface has Gain, Gains, GainMin and GainMax properties.

They are described in the documentation. I’m not sure if anyone implements them.

No offsets.

I’m pretty sure the Qhy specifically does not. Back when Ken and I imaged with a Qhy (and naturally SGP) we attempted to add this access and could not.

If it’s there I’m not adverse to adding it. I’m more interested in how that will be used. If there’s a decent reason to add it we can, but it will take some amount of effort for us to do it and I just want to make sure it’s not in vain.


AFAIK the intent of this was to provide ISO control for DSLRs. Doug George was involved in the meeting where these additional properties were proposed. I think it was a get together between some of the camera manufacturers and application developers at one of the AICs a few years.

Otherwise ask in ASCOM-Talk, maybe Bob Denny will know.

I need this feature, both in fits headers and file names.

Yes, it’s for a QHY. Minicam5f in this case.

In ASCOM now?

I’m assuming that gain is relevant in calibration files like bias and darks? If so there needs to be a way to keep track.

It is not exposed to the ASCOM client, so we have no access to it and can’t put it in the fits header. Ascom does provide access to gain, should the device implement it, but the Qhy ascom driver does not. It is set manually through their property dialog and we cannot access either of those properties.


This is exposed for ZWO cameras in the ASCOM interface, for gain at least, and I would really like to have it available to ensure I calibrate my unity gain subs with unity gain darks, etc.