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Hi everybody! I need your help as I dont know what to suggest. I recently uploaded a foto of m17. My problem is very strange shape of stars (many of them are kind of lines or triangles, or they are like little galaxies). Is it pinched optic or is it tilt and how to get rid of it? https://www.astrobin.com/full/4tq8ud/0/?real Any help is very welcome! 61EDPHII, ASI 1600MM PRO, Antlia 3nm HA |
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| Try to get rid of the filter first and report back. And no processing, just STF. |
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Thank you, Ill try it as soon as the weather allows. Do you mean it could be something wih the filter? I have 1.25 mounted from Antlia. Before I sent my edph in for objective change due to strong CA. |
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Hi Taras_M, when I look at your star shapes, it feels like there is some movement in one of your mount axis. I might be wrong, but this would explan the elongated stars (that appear only in one direction) and the light falloff. The reason for that is hard to guess, but maybe one of your axis is out of balance. Another possible reason might be a problem with the selected guide star. In my case, I sometimes realize, that PHD2 is selecting a star but as time goes by, the light might change and that star is getting brighter until it saturates the pixels of the guide cam. This may lead to similar problems, too. Maybe you had some wind during the exposure. Because the wind is blowing mainly from one diretion, it causes such problems, too. Its a bit hard to tell without any further details of your exposure time, etc. The size of the effect is quite small so maybe wind or bad balance (or even both) might be the best guess at least for me so far. Maybe this helps somehow. CS Christian |
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Thank you, Ill try it as soon as the weather allows. Do you mean it could be something wih the filter? I have 1.25 mounted from Antlia. Possibly. And it is just good practice to reduce the number of variables since it looks like it is a complicate issue. |
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Hi Taras_M, on the top right corner the shape of stars looks different, these lines go in opposite direction. Maybe this is an optical problem with the lens? I know such strange shapes from my DSLR lenses when I try to do astrophotography with cheap ones. (Coma or Astigmatism?) CS, Konrad |
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| Thick filter+coma/startrail+BXT=strange stars |
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Although your problem looks a little different than the one I had you might check fan vibration. ASI cameras are known to have issues with this. To check it just compare images taken with the cooler on and cooler off. I had a problem with elongated stars in one direction. After trying many expert suggestions to no avail I found the Cloudynights discussion linked below. It solved the problem. In the future I will change the fan mounting on any ASI camera as soon as I get it. This may not solve your problem but it is a cheap fix to avoid future problems. https://www.cloudynights.com/topic/837559-fan-vibration-asi2600mc-fixed/ |
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| Does not look like a problem with the mount given the pattern in the top right corner. I expect some combination of tilt and backfocus. |
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| THe OP might not use a flattener (Sharpstar doesn't make them for this unit) or the unit reducer. Given the size of sensor they might not need one at all. |
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Hi all, thank you for your replies! i think I will list my equipment here, to make the suggestions narrower: ts edph ii with reducer on am5. asi1600mm pro cooled to -10C asiair pro, EFW with Antlia 3nm pro. multistar guiding with .5-.6 “ error i will try to make some images w/o filter and will post it here. and I will make some images without cooling to see if its a fan problem |
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| While at it take some images without the reducer, too. That should remove issues with tilt and spacing out of the equation. Or put them firmly in. |
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andrea tasselli: id like to do it, but where may I get good weather? each time i have a weather window i prefer to image and not to investigate. but not this time. i will sacrifice it for finding out what is going wrong with my setup |
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| Don't need to takes loads of them, just few 60s/120s shots at a crowded field will do. Just make sure you are well focused. |
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andrea tasselli: I use autofocus routine on asiair with zwo eaf |
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See image below for reference. The star shapes correspond to "Camera Sensor Too Far Away" for the top half of your image. Since you don't have the same issue at the bottom of the image, you're likely looking at tilt/sagging. |
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André Bremer: Thanks, I used this pics as a reference already. I removed all the small spacers I had before. My back focus is 54,25 already |
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Taras_MThanks, I used this pics as a reference already. I removed all the small spacers I had before. My back focus is 54,25 already You backfocus distance should come out to exactly 55mm using only included spacers (16.5 and 21mm). How did you arrive at 54.25? Also, where did you put your filter? Do you have a drawer or did you attach it to the front of the reducer? If you put it in front, it won't impact your backfocus. Filters shorten the optical path by about 1/3 of their thickness - so if it's behind the reducer, you will have to compensate by adding fine adjustment rings. Antlia filter thickness is about 2mm. That would come out to 0.6-0.7mm of additional backfocus. That said, I am still pretty certain you have tilt in your setup. You can use ASTAP to analyze your tilt (and other aberrations) given a sub. That will tell you for sure. |
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| As everyone else has said, it looks to be tilt and/or backfocus but I did experience similar shaped stars with a William Optics telescope and it was lens cell and a misalignment of the elements. If you continue getting these shapes after thoroughly testing that backfocus is correct and ruling out tilt, I'd contact Sharpstar. They're very responsive and will send a new lens cell assuming you're the original owner and provide them with subs showing the issue. |
