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Hi folks: I seem to have a bit of a nasty tilt issue that has crept up on me. I've never had perfect stars in all corners but the coma was pretty minimal so I didn't let it bother me. In the last 9 months it's become much worse, though, to the point that I brought the telescope into the shop to have it looked at. I was told that the telescope was in collimation, and to achieve the level of precision required to eliminate the tilt I'd have to send it off to WO in China at a cost exceeding the replacement value of the telescope. So here I am, wondering if there's anything I can do about it myself. Here are the more salient details: - I'm using a DSLR - There is no mechanical play in the focuser or the rotator built into the flattener - I have tried numerous back-spacing distances but I still get coma in one corner and astigmatism in the opposite corner - I have rotated the camera using the rotator built into the flattener (on the telescope side, before the flattening optics) and the tilt remains in the same place in relation to the telescope, not the camera/flattener, so I suspect it's NOT sensor tilt or a bad flattener. - I installed the ZWO EAF (auto-focuser) in November, and I can't be certain but it seems to have gotten considerably worse after that, but there has always been tilt since day one with the telescope, so I'm not sure the EAF is the cause, but maybe it made it worse? I'm attaching a test image so you can see the issue. Stars in the upper left are elongated, and stars in the bottom right show signs of astigmatism. Many, many thanks for any suggestions!  Edit: Here's a link to the JPG above |
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Following. I had this exact experience on two brand new flt91’s. Never got it sorted  |
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I had a bizarre issue with my Z61 suddenly not producing a nice star field when I attached a new image train (switched to mono). I was getting similar images as you, and I had to add nearly 20mm of additional back focus to correct it! Tonight I went out and put the same camera on, and now it wasn't working. I took off the additional 20mm spacer and everything was fine. Here's what I deduced my problem to be: The camera rotator you were talking about, well I had apparently unscrewed it out a little bit on accident. Now that it's snug where it should be, my stars are back to normal. I only wasted nearly 1hr 45min figuring that out tonight. I'm not saying that's your issue, but it certainly is something easy to check! |
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Mark Germani: I had very similar issues to this with my Takahashi FSQ85 and my QHY268m camera, not it turned out to be nothing to do with tilt, but a bad match between optics that are a very old design and very small camera pixels, Takahashi recognised this issue and so released another flattener to correct the astigmatism that people were getting, it does not work…☹️ and why should we pay a premium price for a quadruplet scope with a built in flattener, to,have to add yet another flattener to the back, and now face backspace issues…it was a joke, so I got rid of the Tak and bought an Esprit 100. I know this does not help, but though it may be of interest as my issues we’re almost identical… I did a video here… https://youtu.be/YG5jM9-HWGk |
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You may find this article helpful: https://cdn.astrobin.com/ckeditor-files/14318/2023/2cc30650-6fda-40f4-8ea5-1b7cc5babfc2.pdf |
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Chris White- Overcast Observatory: I actually found that very interesting indeed, especially the section where the corrected field was not big enough to cover the sensor size, I think this was part of the issue with my Tak, as I got some small flares on starts about 2/3 from the middle of the frame 👍🏻 thanks for posting…. |
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Chris White- Overcast Observatory: Thanks for this! A lot of it deals with analysing the tilt, but there is a small section on tilt adjustment devices, which would be the starting point for me. I'm not sure the ZWO tilt plate would fit between the flattener and the telescope, but if it did maybe that would do the trick. Anyone have experience using the ZWO tilt plate? CS, Mark |
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| The smaller tilt plate has the adjustment screws on the wrong side so you have to remove the camera for every adjustment :/ |
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See this for adjusting tilt in the daytime, with a very simple DIY laser jig, very effective… https://youtu.be/Gw2oTwb4GjY?si=ipGl7CavT29OP1Li |
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AstroShed: I know it's your video, did this actually work for you once imaging? This is on my agenda to do (I stupidly just smashed up old utilty cupboards I could have used one for this) For me, I'm not sure if the tilt is in my focuser, and I don't think this way would fix that? |
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Luke:AstroShed: Hi, this procedure is for only correcting tilt for anything past the focuser, assuming you keep the imaging train all intact for testing, so if the issue is your focuser then this will not work, also if it’s your focuser the tilt will move depending on where you are pointing in the sky, so that is hard, if not impossible to sort with any tilt adjuster. but it worked for me as my sensor was very slightly off in the camera, and many are nowadays as QC is garbage in these Chinese factories…. when I tested mine the circle on the paper was approx 10mm in diameter, and I got it down to within 1-2mm quite easily… so yes it worked 👍🏻 |
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AstroShed:Luke:AstroShed: Great, thanks for reply. It's odd, I have tilt really just in one corner. I'm still mucking about with spacing, as it's bright moon this week I might try some more hocus-focus and spacing, if not then I have nothing to lose trying your method. I only guess it's somewhere in the focuser as I never used to have this problem and kit hasn't changed. |
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| I have as well the Z61. I struggled with similar issues. I am not a big fan of adjustable flattener. Too easy to get the spacing changed. Anyway, I got a Gerd Neumann CTU and was able to get the corners to acceptable levels. The Z61 is a great little scope, however, I use it with an APSC camera (QHY268). Not sure if I would be able to get the corners "perfect" on FF... Great doc from Chris White- Overcast Observatory! |
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AstroShed: Thanks, that's a very nice solution to sensor tilt! I think my sensor is fine, though - the tilt remains in place in relation to the telescope as I rotate the camera. I'm using a DSLR with no tilt hardware. There is no play in the focuser, and the telescope is in collimation according to the shop. I'm wondering if there's a recommended bit of hardware I can place between the flattener and the focuser which can be adjusted to improve stars in that corner. Any suggestions for tilt plates not specific to cameras, since I'm not using a dedicated astronomy camera? CS, Mark |
