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Hello good afternoon to everyone. I am writing to you since this exceeds my amateur knowledge of astrophotography. In summary, I am studying astrophysics in Chile, and my university has an observatory in the north which we can use remotely. The main telescope we use has the following elements:
I have had good shots, but others not so much, and I have begun to discover a pattern in them, an artifact. And it is the next light that appears in the corner of the frame in all shots. I show you in the photo what it looks like in 3 different filters, and how it looks when stacking the photos. (in the upper right corner it is clearly visible)  At first, I thought it might be amp-glow. but I think I'll rule it out since this looks different. and I could also rule out that it is an external light, since no matter where the telescope is pointed, it is always in the same place in the frame. What do you think it could be? Maybe there is some element, like the filter holder that is somewhat broken, and some light is leaking through there? I'm trying to find an answer to this, because if it's something I can solve remotely, great! But if some equipment must be replaced, repaired, etc., then it is something more complex that requires some clear evidence of the problem. Since it is a remote observatory, and it is managed by another company external to the university. I hope someone knows about the issue and can help me. In advance, thank you very much. |
2.71
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| Light leak rather than off axis reflection? |
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7.90
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| Might be (strong emphasis on the "might") the off-axis guider prism that might leak or reflect light. Just check where the pick-off prism is located relative to the frame. |
1.43
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Is it visible on long exposure dark frames? If not that would exclude amp glow and general issues with the CCD. If possible, you could also try taking a dark frame but with shutter open - to check for light leaks. I had a light leak in OAG where a screw hole wasn't masked correctly by the manufacturer and in effect the OAG, with it's main aperture closed, worked like pin-hole camera ... |
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When were the images taken? Does the light only show up on this particular target, or all other targets? This looks very like off-axis reflection to me. I have a 50cm remote scope that suffered from something that looks very similar. It occurred when there is a moderately bright star that's about 7 degree from my field center. This 7 degree value allowed me to determine where the reflection occurred inside the telescope. When I had a chance to go to the remote site to maintain my scope, I found that there are indeed reflecting surfaces at the expected location. I painted it with black 3.0, and the light goes away. If your images were taken recently, then you should know that Saturn is about 10 deg away from your target. This makes the off-axis reflection a very likely explanation. You can point the scope at Saturn, and take 10 sec exposures after moving telescope away from it by 0.5, 1, 1.5, 2, 2.5,.... degrees until perhaps 15 deg. You can look for the reflection in your images to determine the off-axis angle at which the reflection occurs. Then you can estimate where the reflective surface would be in the telescope. Good luck, to both your observations and astrophysics studies. |
1.20
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| Polar light? |
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1.91
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This might be a stupid question, but when were the optics cleaned last? It might be as simple as a dirty primary / secondary mirror on the Ritchey- Chretien. |
2.86
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I would support the OAG prism hypothesis. It is mainly in the green, pointing towards some AR coatings involved. It does not seem to change shape, too. This could hint towards the Jupiter hypothesis, especially if the shape remains stable over the whole night. It is full moon, and moon is located very close to Jupiter. Maybe a good time for some more test shots, if you consider this hypotheses as plausibls. Clear skies, Horst |
