BAZ Posted March 31, 2016 Author Share Posted March 31, 2016 No, the spider is tight and in line. It's something to do with the optical alignment. It's going to be something dead simple that I am clearly missing, because I am looking too hard. I'll have another go at the weekend. Link to comment Share on other sites More sharing options...
+Ibbo Posted March 31, 2016 Share Posted March 31, 2016 good luck with it , I'm sure you will sort it out Link to comment Share on other sites More sharing options...
Doc Posted March 31, 2016 Share Posted March 31, 2016 (edited) Martyn have a read of this article. It seems to me it might be a case of astigmatism. It explains how to rotate your primary certain ways to get to the root cause of it. http://www.loptics.com/articles/starshape/starshape.html Edited March 31, 2016 by Doc Brantuk and Tweedledee 2 Link to comment Share on other sites More sharing options...
Brantuk Posted March 31, 2016 Share Posted March 31, 2016 That's a great article Mick - I've had it bookmarked for ages and still refer to it now and then. Should sort Martyn out for sure. Link to comment Share on other sites More sharing options...
BAZ Posted March 31, 2016 Author Share Posted March 31, 2016 Thanks Mick, Iv'e bookmarked it and will pay attention. It does look like astigmatism, it has all the key hallmarks of it. I hope all this pain is worth it! Link to comment Share on other sites More sharing options...
BAZ Posted April 30, 2016 Author Share Posted April 30, 2016 Ah well, after absolutely hours of mucking about, tonight's test didn't even wait for it to get dark. It's still not right, better, but not right. I had a look at Jupiter in daylight, and it's now egg shaped you will be pleased to know. I now think the issue might be with the focuser, I mean Christ, how hard can it be to bounce a bit of light off a couple of mirrors. Oh yeah, that hard. Never give up! I will have another go over this holiday. Tweedledee 1 Link to comment Share on other sites More sharing options...
Tweedledee Posted April 30, 2016 Share Posted April 30, 2016 2 minutes ago, BAZ said: Ah well, after absolutely hours of mucking about, tonight's test didn't even wait for it to get dark. It's still not right, better, but not right. I had a look at Jupiter in daylight, and it's now egg shaped you will be pleased to know. I now think the issue might be with the focuser, I mean Christ, how hard can it be to bounce a bit of light off a couple of mirrors. Oh yeah, that hard. Never give up! I will have another go over this holiday. Egg shaped? Jupiter is a bit oblate you know. You sure the scopes not actually at 0.99 strehl? Link to comment Share on other sites More sharing options...
BAZ Posted May 1, 2016 Author Share Posted May 1, 2016 I wish, I think it's within a yard now. I suspect the problem is me and I am missing something really obvious. Never mind it's all good experience. Link to comment Share on other sites More sharing options...
Doc Posted May 1, 2016 Share Posted May 1, 2016 Just read this on a website. It mentions oval stars and stars focusing to a straight line, very similar to what you are getting. Astigmatism Astigmatism (low order) manifests itself as you begin to defocus. The star has an oval shape that when you defocus in the other direction rotates 90 degrees. If bad, the star will focus to a short line, not to a point or dot. Causes in the order of likelihood: the optician figuring in astigmatism due to bad support or preferential area polishing; a mirror support like a sling; flexing due to wedge (one side of the mirror is a tad thinner than the other side); differential cooling. Bad glass (poorly annealed glass) is blamed more than it deserves. In vogue today is the idea that glass has a 'grain'. I've thought so once or twice but always it was traced to the true cause. Brantuk 1 Link to comment Share on other sites More sharing options...
BAZ Posted May 1, 2016 Author Share Posted May 1, 2016 If it's astigmatism, then there is something wrong with the mirrors, but I have had pin sharp views out of it in the past, so I can only assume it's an alignment issue. Thanks Mick. Link to comment Share on other sites More sharing options...
Doc Posted May 1, 2016 Share Posted May 1, 2016 I think it is a support issue causing a bad alignment. I had a similar problem on my lightbridge when I dropped the lower assembly with the mirror in as it was too damn heavy and I lost grip. It went out of alignment and I had to take the mirror out of the cell to get it all back to normal. Link to comment Share on other sites More sharing options...
BAZ Posted May 1, 2016 Author Share Posted May 1, 2016 I have had the mirror out the cell and I marked it to make sure it was put back in exactly the same spot. The mirror clips are loose enough to rotate the mirror and there is clearance so that the clips don't grip it at all. I'll get it somehow. I think I might have put errors in trying to sort it out. I just take it all apart and start from scratch. Link to comment Share on other sites More sharing options...
+Graham Posted May 2, 2016 Share Posted May 2, 2016 From reading through this I think the first place I would start is the focuser. Collimate with the focuser racked all the way in. Then when correct rack the focuser right out and recheck. If the focuser has taken a knock and is now out of square with the tube/secondary it will create the problems you are having. Link to comment Share on other sites More sharing options...
BAZ Posted May 2, 2016 Author Share Posted May 2, 2016 I am thinking this is where the problem lies. You would think it is a simple job to do, but everything else relies on this being right. Of course, then when you collimate you think it's all bang on and in line, but you can be adjusting the mirrors to compensate for the initial error. Everything looks good until you get a bit of star light through it. This is definitely a two brews problem. Link to comment Share on other sites More sharing options...
+Ibbo Posted May 2, 2016 Share Posted May 2, 2016 16 minutes ago, BAZ said: This is definitely a two brews problem. getting serious then don't let any normal mundane things like shopping etc get in the way you will sort it Link to comment Share on other sites More sharing options...
BAZ Posted May 4, 2016 Author Share Posted May 4, 2016 Yay. I am at least in the ball park now. I have been at it since I got home, and I have had everything off the front end and started from scratch again. I have re positioned the focuser, and then aligned it all back up. In the meantime I have been making some bits up to aid the job. One of these is a long M5 bolt, which I put through the secondary fixing hole. Then when you shine a laser at it, you can position the spider to be bang in line with it. You only then have to centre it the other way, up and down. I found Jupiter before it got , well darker, and I can see the four belts clearly and the planet has a sharp edge. It isn't bang on as the moons have some distortion to them, but it's way better and close to usable again. Link to comment Share on other sites More sharing options...
Daz Type-R Posted May 4, 2016 Share Posted May 4, 2016 Fantastic stuff Martyn, glad your getting there. Mines outside cooling as we speak. BAZ 1 Link to comment Share on other sites More sharing options...
Doc Posted May 4, 2016 Share Posted May 4, 2016 well done Martyn. BAZ 1 Link to comment Share on other sites More sharing options...
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