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Over the summer I took the mirror out of my R200SS to wash it. I've done it before and it's always been fine. This time however, on using it the stars were horrid. The first night, the were looking like this during focusing;  So I took everything apart, checked the clips weren't pressing on the primary (they were), recollimated and tried again. I got this (single frame);   Better, but not right, so I tried again (another single frame) and made it worse   To me, the last image looks like I've gone too far with the backspacing, but it's exactly the same setup as I've used many times in the past. The top left and the top centre look odd so I wondered about tilt and, with no particular logic to back it up, I took a couple of flat frames. This is with everything set up as above  and this is with the camera rotated 90º  I used a Rigel align thing to check the secondary placement and then a combination of barlowed laser and cheshire eyepiece to check everything. I've done it many times before and always had decent results. Any ideas?! |
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| I guess you moved and shifted the primary somewhat after the wash-up event (which should really be avoided!). So now your problem is collimating everything up again. Looking at your results the first image (details) showed that your centerline was located to the lower left corner and you should have moved the primary so that the area would have been right in the middle of the frame. Meddling with spacing would only bring you grief so don't go beyond the prescribed spacing from the manufacturer. |
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Thanks. That makes sense as the mirror is held in its cell with little grub screws which tighten plates against its edge. Perhaps I can be methodical with that element and try and get it central. I agree with what you’re saying about the backspacing…other than I’ve recently acquired a William optics ZS61 and reducer and no spacing makes that thing work! |
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| Actually, now I think about it, would that matter? Everything would still be able to be aligned. Are you saying I was simply not collimated well? |
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Piers Palmer: Yes, if the spacing in the CC is correct. |
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| @Piers Palmer Did you end up solving this? I am having similar issues with my R200SS, I am still trying to eliminate whether it is primary mirror clip pinch, focuser slop, backspacing, poor choice of coma corrector, collimation, or tilt in my imaging train. Also using the Corrector PH. About to pull the trigger on a 2.5" Moonlite or Feathertouch focuser because I found my collimation would shift every time I racked the focuser in a different direction, and I definitely have some tilt (about +20/-30micron from corner-to-corner of my 294MM-Pro) when inspecting using NINA and Hocus Focus. I have found the best method to collimate the scope is with my Catseye Blackcat and Infinity XLK autocollimator setup. I am fairly certain my collimation is very close but I am still getting some small egg-shaped or double/out of focus stars in the corners of my image. It is driving me nuts. |
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Hi - I did fix it, but simply by ensuring I could slip a sheet of paper between the retaining clips and mirror itself. I also eased off on the tension between the cork pads and the side of the mirror. Now the stars all appear absolutely fine to me. I had faffed around with trying to put shims under the focuser to square it up, etc, but in the end I was driving myself nuts, went back to basics by returning the scope to "factory settings" and simply made sure the mirror was secure, but only just. Interestingly, the scope was sitting precariously on top of something last night, and the cat decided to have a little explore; of course it did, the cat is evil. The scope crashed onto a hard concrete floor from about 3ft height. Not a mark on it and it's still collimated! The cat was very relieved. |
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| That is good to know. I have already attempted to loosen off my primary mirror clips once already, but then my collimation would shift when the telesope was rotated as the primary mirror would flop about. This resulted in worse stars than when I had started. I have since re-tightened the clips just until I can no longer feel the mirror flopping about, but have not had a chance to test it again. |
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Newtonians are painful basically. I reckon it took me two years to get it to work consistently and now I just collimate every session (so about twice a year) using a Barlowed laser, and leave it at that. One day I might treat myself to a factory-fresh one and hopefully never really have to fiddle at all! |
