Diffraction Pattern Around Bright Stars

Acquisition Deep Sky Artifacts Troubleshooting
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Jeff Ridder avatar
Jeff Ridder avatar
I recently re-wickered the imaging train on my TEC140ED and am now seeing a diffraction pattern around some bright stars. Did not see this with TEC140ED + AP QTCC + QHY OAG + 36mm Chroma filters + QHY268M. But am now seeing this with TEC140ED + TEC FRC + Gerd Neumann CTU + Sagitta OAG + 2" Chroma filters in QHY CFW3L (with Buckeye Stargazer filter masks) + QHY600M. It happens only on some bright stars toward the outside of the frame, and only on some filters -- have seen on R, G, and Ha (5nm) so far. So, it’s apparent on the red end of the spectrum, but haven’t seen in Blue or OIII. Below is from the lower left corner of an Ha frame. I dialed out the tilt with the CTU and confirmed with ASTAP, so pretty happy that I'm reasonably tilt free.Any thoughts on cause and how to fix?
Rouz Astro avatar
Rouz Astro avatar
Interesting, I'm using a similar combo - QHY600M Sagitta - Chrome NB and Astronomik RGB. I haven't seen these artifacts.
This camera shouldn't exhibit microlensing artifacts either.

Could it be caused by the corrector? Have you tried flipping the filters?

CS
Rouz
Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
I've seen this before on bright stars when I had a little bit of tilt in the image train.  It was interesting to see the effect change with tilt adjustments.  I'm not sure what caused it in my case, perhaps a slightly tilted glass plane in a filter or protective window or even sensor cover slip???  I've also seen this become more apparent in really good seeing, so perhaps it is a strange artifact that you might not otherwise see in average skies. 

On the topic of microlensing… not to be pedantic, but microlensing is a gravitational effect caused by galaxies…  I think you are referencing microlens diffraction patterns, which is very different.
Jeff Ridder avatar
Jeff Ridder avatar
Pretty sure I’m as tilt free as I can be thanks to the massive CN thread. Hocus Focus and ASTAP agree. Flipping filters is worth a try. Seems to affect some filters more than others.
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