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Reflection: Ap-155 w/0.76 Telecompressor, ADATCC1, 5-Position filter wheel, STL11k, Astrodon LRGB (NIR blocked) filters

Below are several full frame, reduced resolution 10 minute exposures taken with the above optical image train. Please note that the reflections are always centered about the optical axis. Additionally, the reflection gets "flattened" as the bright star is positioned further away from the center of the image and becomes more oval as the star is positioned nearer the center of the image.


The flat frame below shows a radial pattern (like rays) of brighter light seeming to be sourced somewhere outside the frame. I have not seen any such pattern on any flats in prior flat exposures either from this camera on other optical trains or my other cameras. This pattern is on all flats from multiple nights and always coming from the same area.


I have taken other images such as M 45 and they also exhibited reflections that seem to follow the same pattern. Also note, that the images below may be “flipped” relative to one another due to the meridian position of the telescope when taking the image.


I need help determining the cause of this reflection. I would like to know what the potential sources of the reflection are and what things are highly unlikely. I would also like to know what types of testing I can do to try and isolate the problem. This is in a remote observatory, so time on the equipment is precious.


Background: I have been using the AP 155 with the Field flattener and a ST10 XME for several years and never seen any reflections. I have been using my STL11k for several years with my FSQ-ED and not noticed any reflections. The STL11k was sent to SBIG to have a capacitor replaced to fix a banding problem, just before I installed it on the AP. It is possible (although I would think unlikely) that something has changed in the camera. The main changes in the setup are replacing the ST10XME with the STL11k and replacing the Filed Flattener with the 0.76 Telecompressor. This also involved removing a 4 inch extension tube from the previous setup.


Horsehead centered
Yellow arrows point to bright stars and reflections

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Alnitak far left
Reflection is flattened

Alnitak far right
Alnitak reflection appears flattened

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Flat of Lum filter
Notice strange radial light pattern

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