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Hello all, My recent two images have been shot at 300 sec light subs, and I am seeing evidence of an internal reflection. scope: 120 Esprit flattener: 1.0x stock flattener camera: 2600mc Images: https://astrob.in/fn47cv/0/ https://astrob.in/m9t379/D/ The first image shows a faint red ring that passes through the galaxy in the widefield version. The second shows a red ring of light that it at the top upper right and is in proximity to the blue star (top right). Its annoying. To say the least. At least I think that the artefact may be generated from an internal reflection - and I am guessing that its sourced from the 1.0x flattener within the 120 esprit, and am at a loss about how to fix it. My hypothesis is that some IR light is being reflected and the camera is picking it up. Depending upon the shot the ring of light changes placement in the frame, so likely is an abberation of the combination of the scope, the flattener and the camera. Some have mentioned that perhaps a luminance filter will fix the problem, however the camera (2600 mc) already comes with a IR/UV cut filter before the sensor. Thus I am unclear as to whether duplicating this approach will help. I mean, I could always go ahead and try it, but I thought I should pose the question on the forums first. My hope is that some of you may have experienced this issue (or something similar) and have come upon a solution. At least I hope this question will generate some thoughts. As I am relatively new to AP, this glitch in my scope's performance is beyond my own experience. Thanks for your interest... I would be grateful for any input. Best Ian |
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| Maybe they misplaced the window and you got an AR coated one instead (from the Mono series)? Worth checking, IMO. |
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andrea tasselli: *Hi Andrea, good suggestion! I will check it out. |
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Hello all, I think I may have solved the issue. I was looking at my flattener/backspacing arrangement for the 120 esprit and noticed that two of the 10 mm spacers I have used are of a very cheap quality. I mean they screw together and hold everything properly, but the paint on these two units is glossy. Holding the assembly to light and peering through it revealed that there was significant reflection being generated by these two spacers. My plan is to paint them with dull flat black paint and then test to see whether the internal reflections are diminished. Thanks, Ian |
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If anyone is interested here is how I fixed the spacers (blackening of the interior). The glossy paint was on the threads on the interior, now replaced with flat black, an old telescope atm trick. |
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More follow up...(my self generated thread is growing, ha ha). Here is a test of NGC 891, shot in Bortle 2 with a lot of interfering aurora activity. I can't see any red ringing artifact now - but many of you have sharper eyes... @Thilo ? @Rodd Dryfoos ? Have a look and let me know. This image: Esprit 120/flattener/AP900 mount/2600mc camera: 1x1, gain 100, 20 x 180 sec, calibrated with flats, testing my fix  |
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Hi Ian, indeed I can't see on my monitor the red ring artifact that was clearly visible in the other two images of yours. It seems that you have got it!  Congrats! Best - Thilo
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| Yay!! |
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| Way to go Ian! You are a good and persistent sleuth indeed. -john |
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| I can’t see a red ring, but I do see INCREDIBLE detail in the dust band! Bortle 2 indeed. The scope and mount are not bad too, and of course, the astrophotographer is no slouch! This is a very high end image |
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John Favalessa: *. Thanks John, I appreciate your input! |
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Rodd Dryfoos: * Thanks Rodd! Much appreciated.  |
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Sometimes painting the shiny parts helps a lot. The darkest paint I have seen is this one. CS Rouz www.RouzAstro.com  |
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A bit of curve work in photoshop/gimp etc can help reveal any artefacts ... apologies for messing with your images but its interesting to see those 'hidden' gremlins. |
