Hello, I am currently shooting with my 10 inch RC and like it very much. After some nights I wanted to check my results and stacked my images. What did come out was nice, but the stars showed some weird additional spikes and flaring. Do you know what could be the issue? The RC was collimated on the stars but this was some weeks ago. Pinched mirrors? Weird reflections? Miscollimation? Ghosts haunting my RC tube? I would be very glad, if some of you have some tips for me. I attached a crop of my stretched stack with the brightest star in the frame. The sub exposures in L R G B look the same, but less bright. This pattern repeats on other brighter stars. Regards  |
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See this video by Adam Block: https://m.youtube.com/watch?v=S_1nXlzJspIHe has the same issue which he says comes from imaging close to the celestial pole with some PA error (or leveling error, according to another of his videos) that causes field rotation such that star diffraction spikes in an integration don’t line up even though the stars themselves are aligned. He describes the issue and how to deal with it starting about half way in. Cheers, Scott
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Scott Badger:
See this video by Adam Block: https://m.youtube.com/watch?v=S_1nXlzJspI
He has the same issue which he says comes from imaging close to the celestial pole with some PA error (or leveling error, according to another of his videos) that causes field rotation such that star diffraction spikes in an integration don’t line up even though the stars themselves are aligned. He describes the issue and how to deal with it starting about half way in.
Cheers,
Scott Thank you, I looked into it and after that I blinked through my data. I can say that my main spikes are not jumping around like in Adam's video. They are staying in place. Good tip with the proximity close to the celestial pole as I'm shooting in the constellation camelopardalis. Regards Tobi
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Typically you might have additional obstructions in the light path other than the secondary holder and spider. An image of the Fresnel rings should be telling of the possible culprits.
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Tobiasz:
Thank you, I looked into it and after that I blinked through my data. I can say that my main spikes are not jumping around like in Adam's video. They are staying in place. Good tip with the proximity close to the celestial pole as I'm shooting in the constellation camelopardalis. Do the extra spikes show in the individual subs (which would be consistent with Andrea's thought)? If not, seems like they must be in different positions sub to sub to cause the extra spikes in the integration. There would also need to be close to half to not get rejected, so maybe if they're grouped, it wouldn't be as obvious blinking through them? Cheers, Scott
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This looks a little different as it's not a rotation of all the diffraction spike pairs, just one. It also looks like it's mostly in your B and L stacks.
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Yes, the extra spikes show in the individual subs, does not matter which one.
I use the TSRCFLAT2 as flattener with 109mm back focus, regarding additional obstructions my OAG is the first thing that comes to my mind. It has a large prism tower including a immense 12x12 prism. It protrudes in the light path, right in front of the filter wheel and the camera window. From the frontal view I would guess there are 1 to 1,5mm of space between the prism edge and the sensor area. Maybe that's too close? I try to move back the prism tower so the gap is greater and see how it goes.
Regards
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I would say that's a strong possibility. It does look like a single item is causing this.
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I looked down my light path without the main camera, saw nothing unusual but the OAG. Against the light of the day I can clearly see the glue behind the prism producing nasty reflections which may affect my sensor I think. The glue looks reflective and curvy because its not applied evenly, which may explain the consistently different thickness of the additional spikes. Painted it over with a mixture of black matte school board paint and microballs, which already helped me with my RC baffle tube. Let's see if it helps, it is starting to annoy me especially after a night without moon  Thank you for your input.
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