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First broad band image with the AG optical FA12 Convergent with a 6200mm. Trying to trouble shoot a few things and will bounce this against the hive. I know my flat frame did a poor job, and I think I know why (flat panel was too small for the aperture). Seeing was quite poor that night. Two issues that I wonder if I can get some suggestions. 1) I am still new to spider veins and diffraction spikes (been imaging with SCTs/ Refractors). There is an extra long diffraction spike after stacking on the bright Hatysa. I know there are other issues with this image too. Is this due to a slightly misaligned spider vein blade? 2) There is an artifact that is on the edge of the right lower corner. Assuming it is a light leak of some sort? ![]() |
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My personal opinion is that what you see in the lower right corner is not a light leak but I do not have a reliable answer what it might be - a light leak does not have such a defined shape. In that area around M42, aren´t there some smaller nebulae? And regarding those long spikes - I was told, that long and thin spikes come from thin spider arms. If they were misaligned, they were wider/double etc. But that is what I was told, maybe correct, maybe not - but it would make sense to me. CS Georg |
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Georg is right, misaligned vanes will cause double spikes. Those are absolutely perfectly aligned. Side question, how's the blue bloat on that scope? |
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The "extra long" spike isn't actually from that star, Hatsya, but from another one off-field, curiously aligned as it were. A similar situation is what you see on the far lower right corner. The "blob" is a weird off-axis reflection of a bright stars in the corrector optics. I had few of mine with a custom focal reducer but I always attributed that to the poor coating of the latter. |
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Georg N. Nyman: Thanks George for saving me the trouble of messing with the spider veins. The reason I don't think the blob in the right corner is a real structure is because I have seen it in other frames, albeit on a different OTA and completely different imaging train that looked very similar. For example I have seen it in this frame (part of M31 with the C11 and 2600mm pro, Starizona 0.7x reducer). You can see it to the left and to the bottom right. ![]() Brian Puhl: I still have very limited frames on the blue filter. I have been imaging mostly in narrowband so far. Can't make a judgement yet. From the limited time I am with it I haven't seen much in the way of bloat though. andrea tasselli: Thanks Andrea. That seems very plausible! I did look to see if there are any extra bright stars just outside that field of view in the direction of that spike and I am not sure I see any on Telescopius. I am stumped. ![]() I sure hope the blob is not caused by poor corrector lens coating. It is very dirty though and I have not attempted cleaning it. |
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Asraf, Those "blobs" are caused by internal reflections off the internal baffles. When I first started imaging using a visually oriented Celestron SCT, I had tons of them. Consulting with the manufacturer, they told me to flock the baffle exiting the back of the scope. I ended up flocking all the internal surfaces and the loops disappeared. They occurred only with very bright stars, even if they were out of the field of view. Ron PS - Here is an example of what I was seeing and why I think you have the same issue. This image has a lot of those loops. ![]() |
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Ron: That makes sense. My baffle is flocked, but I wonder if these reflections are coming from the interna focuser tube. It is the only thing that is shared between those two images. Thanks for the feedback! |
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Let us know if that solves the issue. I’m pretty sure it will. |
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Your spikes are very nice. I need to correct the following that was miss-stated before. A) Unperfectly othogonal vanes will produced two crossing spikes per vane direction (i.e. if you have for vanes that form a cross, you will get two "X" shapes slighly missaligned. B) doubled but non-crossing spikes reflect poor focus of the image. See my old M45 combining a bit of both problems... https://www.astrobin.com/full/oe78vz/0/ CS |
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Your spikes are very nice. Thanks that makes sense. Do you have any suggestions what might be causing that appearance of a "long diffraction spike" in the image? |
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Ashraf AbuSara:Your spikes are very nice. @Ashraf AbuSara My understanding is that large vanes produce very intense and long spikes. I have 0.5mm vanes and yet my first capture of M42 with that scope presents very very long spikes on that star too. This is a very bright star. See for yourself : https://www.astrobin.com/fhk68n/ However, a more recent capture, with the same gears, exhibit more reasonable spikes. https://www.astrobin.com/otnl1r/ I suggest to work on the star processing to stretch less the low light to get rid of that. That is what I did on the second image. |