How do I do Flats on Coronado PST ?

[Cliff (Clifford)]

Trying to produce some flats for my Solar imaging using a Coronado PST with a ZWO174MM .

Getting reasonable results but want to even out the images using flats , the only thing I've seen is to defocus but can't defocus enough on the Coronado .

Appreciate the help
Cliff

[Merlin66 (Ken)]

Cliff,
Not an easy one. Using flats is much easier when you have just surface detail in the image.
When you have a full disk surrounded by “sky” it’s difficult to register the flat and smooth the “sweet spot”
One semi-solution is to use the thin plastic bag trick. A thin clear plastic bag over the objective and take a flat where the histogram is 80%.
No guarantees of success but worth trying.

[SteveInNZ]

As an experiment I just tried putting a "diopter" lens on the front of the PST and that looks like it might be worth pursuing. The one I tried gave an out of focus disk, about twice the size of the focused Sun. I didn't get a chance to try much else before it clouded over.



Steve.

[Merlin66 (Ken)]

Steve,
Interesting variation.
Look forward to hearing the results.

[Cliff (Clifford)]

Thanks Ken,

Yes would be easier with more surface visible .Will try the plastic bag though
thanks
Cliff

[Cliff (Clifford)]

Thanks Steve,
Not sure I have something like that, a reducer I have but only 2" .
I'll keep experimenting quite pleased with what the little coronado can show both visually and photo wise.
Cliff