Quote:
Originally Posted by SkyViking
Hi Steve,
I provided my opinion on what I could see in your image, based on the information you posted. I don't think it amounts to discounting anything.
The main problem, as I see it, is still that your diffraction spikes lie very close to the dust disc plane. I have attached an image which shows my image overlaid on yours. Notice how the diffraction spikes in your image nearly covers the area where the dust disc appears in mine. Surely that will not help with detecting it.
Reducing the glare is paramount, and I also believe the wire spider I'm using makes a big difference. I don't know what kind of spider you are using but there just seem to be more glare in the images you posted than what I saw in mine.
The second image attached (Kalas & Jewitt, 2000) is a good reference, it's upside down though.
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The larger the secondary the heaver the spiders but some of that is light scatter. I have some on my excellent 20" RC optics. You can get extra scatter from an unmasked edge on the primary, a field flattener or even dirt on the optics. Also poor seeing can cause the star halo area to expand.
If you can use thinner spiders that is excellent but my secondary is almost 8" across (larger than my first 6" reflector) so one cannot use wire to be stable. I fght bright stars with longer exposures so sometimes I will cut my subs down to just overwhelming the read noise.
Even with an expensive excellent system bright stars can be an issue to get a clean star profile. It seems no matter what you pay you have to tweak and modify to get things right.
This is good discussion as it helps us understand how to better utilize our imaging systems.