Flats for whole disc solar, IMX178 in particular

[AstroMathmo]

I am using SCPRO 4 to do some solar work and it is fantastic.

I wondered if I could get a bit of help on optimising the collection and use of solar flats from within SCPRO? I do have a couple of blobs on the sensor, and have an IMX178M in my GPCAM3 178M from AA. I seem to be a rare sufferer of the residual grid pattern known for IMX178M chips. Decent flats seem to help a lot, and I've got that working when using a Quark on my 61EDPH scope, as a bit of defocusing gets me a pretty uniform field and auto-application of the flats seems to work fine and mostly kill the pseudo-Bayer stuff whenI'm working at the red end of the spectrum.

Where I'm having less luck is with whole disc images (so bright disc with dark surround) - I can't defocus enough to get a uniform field (blobs and grid aside). So wondered what people do to manage that? I've heard talk of cling film, lobbing a Barlow on, plastic bags but so far, at least when I'm imaging at the red end, I've yet to get a usable signal with a plastic bag. It's dark with an Ha filter on my wedge.

**Geek warning**

Another thing I can try, to deal with the grid kicking up at the red end, is to make a pseudo flat with 2x2 arrays of scale factors for the pixel sensivities for any given filter, and load that into SCPRO. My gear is getting cleaner and that might just kill the residual pattern noise. To that end I wondered what format SCPRO expects for a flat file so I can make one in Mathematica.

thanks to all.

[admin]

Hi,
my approach for solar flats is translucent plastic film. A good source is the inner bags in packets of breakfast cereal.However, that may not be sufficient to deal with a whole disk image, since I have to make sure the whole image is filled with solar disk when using it.

I wonder if two layers or that sort of translucent plastic, separated by maybe 1cm would work? It would seem worth a try anyway as it is easy to source.

As for generated flats, FITS files or PNG files at 16 bits per pixel monochrome are the best bet, with pixel values in the range 0..65535

Fits requires a certain amount of care with the BZERO header to ensure that the 16 bit values are interpreted as unsigned 0 to 65535 not signed values.

cheers,

Robin