+Ibbo Posted February 5, 2012 Share Posted February 5, 2012 I believe are caused in my case on the 132 by the series of screws which hold the objective in its cell There are 3 rings of 6 holding the triplet in place. I've backed them off a bit and it is a little better and it is worse when cold not sure i backing them off further will help also the bezel is really tight to loosen this I need to make a tool It can also show its self on mirrors I had a reflector which had the secondary glued down and showed all stars as triangles I released the glue and stuck it on with a felt between the holder and the mirror which cured the problem Link to comment Share on other sites More sharing options...
Brantuk Posted February 5, 2012 Share Posted February 5, 2012 Thanks for this Steve - I think only the folks who've gotten deep into AP will know this - it's been a topic of curiosity for lesser experienced (like me) for ages and this is the first insight I've had. So it's nothing to do with figuring then - but more with how the lens is held in place? Link to comment Share on other sites More sharing options...
Rusty Strings Posted February 5, 2012 Share Posted February 5, 2012 Cheers Steve. I was aware of the problems of over tightening the primary on a newt but never heard of probes with fracs Link to comment Share on other sites More sharing options...
BAZ Posted February 5, 2012 Share Posted February 5, 2012 I have just recently been on Philj's website re Refractor collimation, as I had a problem with defocused stars. The bezel holding the lens in had been put on by a gorilla, it took some getting off, and the three shims that separate the two lens were not at equal spacing's. I cannot get it to collimate perfectly, as the focuser is rubbish, there is loads of slop. But it's now happier. />http://philjay2000.tripod.com/ Link to comment Share on other sites More sharing options...
Guest ollypenrice Posted February 5, 2012 Share Posted February 5, 2012 The pattern certainly seems to be that cold makes the problem worse, presumably as the cell contracts around the glass. Would a dewheater strip be a good idea even in dry weather? Optics are super sensitive to mountings. A visiting professional had a look at my Dob's secondary and declared it distorted by too rigid attachment to its PVC supoort. It was held on by the usual three blobs of silicone. However, Ralf said not to do it that way but to make a small ring of silicone instead. This done the mirror stopped inducing astigmatism. It is a fair old chunk of glass so I was amazed that the support could distort it but a fraction of a wavelength isn't much... Olly Link to comment Share on other sites More sharing options...
Guest NadeemShah Posted February 5, 2012 Share Posted February 5, 2012 (edited) It would be nice to have pictures of the adjustment routine, so it would help anyone with these issues.. Edited February 5, 2012 by NadeemShah Link to comment Share on other sites More sharing options...
philjay Posted February 5, 2012 Share Posted February 5, 2012 (edited) Hi Steve, The pinched optics are very common on these scopes, my old 102ED (which was basically a megrez under a different name), doublet had the same problem, the 3 screws around the perimeter were pinching when temperatures dropped and gave a strange but quite attractive set of diffraction spikes. The screws are for alignment of the elements of the objective in relation to each other and shouldnt really be touched IMHO, back em off now in cold weather and the elements may be too loose in warmer weather.When I 1st got my 102 I was going to back these off but chickened out. It makes me wonder if there is any padding between the tips of the screws and the edge of the glass. I reckon my 102 didnt have any because the spikes were so sharp, metal on glass urggghhh. But in summer the spikes dissappeared. Modern ED glasses have been proved to be softer than the old crown/flint glass (just ask Neil English) so will distort more than say the equivalent achromat if it has uneven pressure on it. There was alot of talk re this on various scope forums a few years ago when these scopes hit the market, it wasnt just WO and Orion USA it was Stellavue and others, all made by the same firm at the time (Kunming). However other manufacturers took up this method of alignment and it was seen in a few other cases. Funnily enough my Meade 127 has 2 lots of these screws (triplet) but shows no sign of pinching in the cold. Thanks for dropping by my website Martyn, yep overtightening the objective locating rings on the traditional lens cells is a common problem and makes a vast difference to the image but it was an even distortion due to the pressure being placed around the edge of the objective not spikey or elongated as in this case Martyn If you want I can take a look at your scope for you, I have rescued quite a few thats had finger trouble. My 4" F15 had been got at by someone who had lost one of the foil spacers between the elements so stuck a bit of *** packet foil in there. This caused a ghost image. It had me scratching my head that one did. Phil Edited February 5, 2012 by philjay Link to comment Share on other sites More sharing options...
+Ibbo Posted February 6, 2012 Author Share Posted February 6, 2012 I have just recently been on Philj's website re Refractor collimation, as I had a problem with defocused stars. The bezel holding the lens in had been put on by a gorilla, it took some getting off, and the three shims that separate the two lens were not at equal spacing's. I cannot get it to collimate perfectly, as the focuser is rubbish, there is loads of slop. But it's now happier. http://philjay2000.tripod.com/ Mmmm same gorilla but I think hes been on steroids Link to comment Share on other sites More sharing options...
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