SharpCap Forums

I'm venturing into Flat Frames with my ZWO ASI294MC Pro camera and have a few questions:

- When I created flats, I did NOT have the option to "Capture and Subtract Bias Frames..." Any idea why? From what I've read elsewhere, I thought this was important to do. The check box would not let me check it.
- The instructions suggest that a very low gain should be used. This is contrary to things I've read on Cloudy Nights that recommend that the SAME gain setting be used for Flats as will be used for the lights. Is there something about SharpCap that requires low gain Flats?

Thanks! Mark

If you already had dark frames captured and added then you can't capture flats.

Is the issue possibly that I had already selected a Master Dark into the Preprocessing "Subtract Dark" Area?

Hi,

Yes, if you have dark subtraction frame selected then the bias option will be unavailable. Using a dark is an even better option than using the bias frames, but you must make sure that the dark frame you use was captured at the exposure lengthy and settings that you are using for flat frame capture. If you're dark was captured with different settings then it's better just to use the bias frame than to use a mismatched dark.

Cheers, Robin

Thanks Robin! Just to clarify:

- If I'm going to use both Darks and Flats, create the Flats WITH the Bias option selected but do it BEFORE selecting anything into the DARKS area?

Regarding my second question, what gain should I use when creating the flats? The same as I intend to use for the light frames or something small (like zero)?

Mark

Hi,

Low gain is good for flats as it leads to reduce noise and you need to take less flats to get a smooth master flat. However it is not essential – you use a high again you just need to let SharpCap capture more flat frames to let the noise average out.

Cheers, Robin

Hi Robin,

Are you talking overall noise or the read noise? My ZWO ASI294MC Pro camera has a higher read noise (6-7 e-rms) from gains of 0-119, then it drops to 1-2 e-rms after gain settings of 120 and larger.

Mark

Yes, sure. I have Asi294 and i usually take flats at unity gain that is 120, as you already said.
So the lowest gain regarding the lower read noise is unity 120 gain indeed...But in general gain isn't so important for flats...

Hi,

I'm talking about the total noise here as a fraction of the frame brightness, so basically what's the percentage deviation due to noise in the brightness of the flat frames.

Cheers, Robin

IPPIU: Are you using SharpCap for Live Stacking with your dark and flat frames with your ASI294MC camera? If so, can you please let me know what light panel you're using and your complete process? I'm getting some strange color issues and am wondering if it's my light panel or some other configuration issue.

Thanks!!

Mark