1 reply to this topic

[jimmyeubanks]

Good Evening,

 

I ran into an issue with my flats shooting broadband for the first time.  As I look back at my dual narrowband images, they actually had the same problem, but background extraction had worked well to alleviate most of the issues.  I have been shooting with my first astrophotography dedicated camera, the ZWO ASI2600MC Pro, for about six months now and this was the first go at broadband. 

 

After calibration and stacking, the master light still retained a large wide ring around the center of the image where the major transition occurs with vignetting of the optics of my refractor.  I watched Adam Block's video explaining how to debunk flat problems and tried the method of using pixel math to alter my master flat.  After experimenting with different values, I found the expression $T-0.025 gave a near perfect result in flat fielding the light frames.  My flat frames are dark subtracted, as well as my lights.  

 

My flat subframes were taken with 5 second exposures with a maximum ADU of 34400.  Given the above expression used to alter the master flat, is there relationship that I can establish from this to determine what ADU would have worked best?

 

Thanks for you insight!

 

Jimmy

[bignerdguy]

You can also use the pixel math expression:

 

$T -/+ (xxxx/65535)

Where $T is the currently open image

 

xxxx is the amount you want to adjust by

 

65535 is the Max ADU for a 16-bit image.

 

and with the -/+ you can either add or subtract depending on what you need to adjust the ADU by.

Edited by bignerdguy, 23 April 2025 - 02:25 AM.