My latest star test on my recently acquired LOMO Astele 150 Mak-Cass determined that I had some coma from misalignment. It manifested itself at high power as a tiny pair of tails on brighter stars. The diffraction pattern on one side of focus clearly showed a teardrop shape, with the pattern much less pronounced on the other side of focus. It is worse near one particular side. The diffraction pattern changes considerably from edge to edge when the star traverses in one direction, and hardly any at all when traveling across perpendicular to the worst case direction. That seems to indicate a tilted corrector plate to me.
I took the OTA to the local dealer that once sold them, and we looked closely and determined that somebody had tried doing some aligning. There seemed to be too much pressure applied on one of the trio of the push-pull cell's collimation screw sets, the pair of tiny set screws that push in from the front against the larger puller screw that sits between them. One screw had a marred head from the jeweler screwdriver slipping off it.
I ordered Suiter's book on Star Testing Astronomical Telescopes, and I have experience in collimating my Newtonian scope. I will guess the corrector is a bit tilted and pinched in the cell at this point. If anybody has any experience with this particular series of LOMO Mak-Cass scopes, I would appreciate any insight you could give. The dealer said to have a go with collimating it, just go slow and take it easy, but I would rather wait and see what the book says and see if everything works out according to the book. It looks almost impossible to apply too much pressure to permanantly hurt the corrector, unless the springy section the small setscrews butt against were shoved all the way into the glass, but a person could take the spring tension out of the push-pull cell before that occurred.
Still, even with the coma tails, it's obvious that this scope has a lot of potential. Moon views were fairly sharp and Saturn was as detailed as in my 8" SNT. It's obvious that the worst aligned edge of the corrector is what causes the coma tails on bright stars. Faint deep sky objects seem hardly affected and the scope has very high gross contrast (contrast between separated objects). The price I got the scope for reflected the fact that I would need to put a bit of effort into it to get it back to factory original collimation. It was acknowledged the scope had been apart for an internal repair. It has a very clean external appearance with no scratches of significance anywhere and absolutely no dents, so the scope has never taken a hard fall. Two screws had been lost from the finder scope mount, so the scope may have been subjected to lots of vibration in transit, but there is no paint rubbed off to suggest rough traveling conditions.
My biggest concern is how much pressure should be applied to the corrector with the push-pull alignment screws, and my best guess is there should be a "torque angle" to be evenly applied by the puller or pusher screws. The angle turned on the small screws after making contact will probably determine a clamping force through the springy part of the retaining ring. My guess is that the bigger trio of screws actually sets the corrector tilt while the six little setscrews set the clamping force.
Phil
I took the OTA to the local dealer that once sold them, and we looked closely and determined that somebody had tried doing some aligning. There seemed to be too much pressure applied on one of the trio of the push-pull cell's collimation screw sets, the pair of tiny set screws that push in from the front against the larger puller screw that sits between them. One screw had a marred head from the jeweler screwdriver slipping off it.
I ordered Suiter's book on Star Testing Astronomical Telescopes, and I have experience in collimating my Newtonian scope. I will guess the corrector is a bit tilted and pinched in the cell at this point. If anybody has any experience with this particular series of LOMO Mak-Cass scopes, I would appreciate any insight you could give. The dealer said to have a go with collimating it, just go slow and take it easy, but I would rather wait and see what the book says and see if everything works out according to the book. It looks almost impossible to apply too much pressure to permanantly hurt the corrector, unless the springy section the small setscrews butt against were shoved all the way into the glass, but a person could take the spring tension out of the push-pull cell before that occurred.
Still, even with the coma tails, it's obvious that this scope has a lot of potential. Moon views were fairly sharp and Saturn was as detailed as in my 8" SNT. It's obvious that the worst aligned edge of the corrector is what causes the coma tails on bright stars. Faint deep sky objects seem hardly affected and the scope has very high gross contrast (contrast between separated objects). The price I got the scope for reflected the fact that I would need to put a bit of effort into it to get it back to factory original collimation. It was acknowledged the scope had been apart for an internal repair. It has a very clean external appearance with no scratches of significance anywhere and absolutely no dents, so the scope has never taken a hard fall. Two screws had been lost from the finder scope mount, so the scope may have been subjected to lots of vibration in transit, but there is no paint rubbed off to suggest rough traveling conditions.
My biggest concern is how much pressure should be applied to the corrector with the push-pull alignment screws, and my best guess is there should be a "torque angle" to be evenly applied by the puller or pusher screws. The angle turned on the small screws after making contact will probably determine a clamping force through the springy part of the retaining ring. My guess is that the bigger trio of screws actually sets the corrector tilt while the six little setscrews set the clamping force.
Phil
