erick
27-03-2007, 01:20 PM
Now I own an 8" Bintel reflector and have started attempts at collimating, I'm reading all that I can find.
I'm interested in how detailed an approach to this can be, eg:-
http://www.iceinspace.com.au/forum/showthread.php?t=18423&highlight=catseye
and I've pulled, off the "catseye" site, a major article on collimation:-
http://www.catseyecollimation.com/mccluney.html
and I'll read this soon.
But, my first question is "How close is close enough"? I know the answer will be - "It depends". OK, so currently I'm interested in visual rather than photography (with the reflector, anyway). I'm at the very beginning with a scope and my targets won't be super ambitious.
Proposal - set up the scope in the observing location, cooling fan on primary for about an hour. Check that the secondary mirror seems well centered under the focuser (shouldn't change with normal handling) using my "sight tube" - 35mm film cannister with 1/16" hole in bottom); drop in the laser, don't do up the eyepiece lock screw, check laser is sitting flush against the 2"-->1.25" adapter (2" focuser) and adjust the secondary so that the dot falls in the centre of the primary (I have a donut centre "spot" with a generous centre hole that the laser fits inside). Adjust the primary mirror until the laser returns through the hole in the collimator. Is that good enough? What is the relationship between the mm the laser dot is off centre of the primary or the centre of eyepiece, and drop-off in viewing quality - rapid, slow??
My second question is about the mechanics. The mechanical design of the primary adjustment, I think I understand. It seems to me that I can adjust the three collimation screws independently - ie. I don't have to screw the other two out to compensate for having screwed one in (unless I was really worried about my focal length to the nearest mm or fraction thereof?? On thinking about it, any change in distance of the primary mirror from the secondary is probably compensated for in the focuser?). But I don't understand the mechanical design of the secondary (we are talking about a Bintel premium 8" reflector, vintage Nov 2006). I will pull it apart at some stage to get rid of the screws (replace them with threads with wingnuts I can operate by hand - yes, I may have to "soup up" the dust cap by adding a raised section to accommodate ;)) but, in the meantime, do I need to move the three screws in conjunction with each other, rather than independent of each other? Will I bend or break something if I didn't move them together? I notice that they are relatively tight to adjust, which concerns me a little. Tight enough so that, as I turn them, the spider flexes then relaxes - I don't like that at all.
Thanks for your help. :)
I'm interested in how detailed an approach to this can be, eg:-
http://www.iceinspace.com.au/forum/showthread.php?t=18423&highlight=catseye
and I've pulled, off the "catseye" site, a major article on collimation:-
http://www.catseyecollimation.com/mccluney.html
and I'll read this soon.
But, my first question is "How close is close enough"? I know the answer will be - "It depends". OK, so currently I'm interested in visual rather than photography (with the reflector, anyway). I'm at the very beginning with a scope and my targets won't be super ambitious.
Proposal - set up the scope in the observing location, cooling fan on primary for about an hour. Check that the secondary mirror seems well centered under the focuser (shouldn't change with normal handling) using my "sight tube" - 35mm film cannister with 1/16" hole in bottom); drop in the laser, don't do up the eyepiece lock screw, check laser is sitting flush against the 2"-->1.25" adapter (2" focuser) and adjust the secondary so that the dot falls in the centre of the primary (I have a donut centre "spot" with a generous centre hole that the laser fits inside). Adjust the primary mirror until the laser returns through the hole in the collimator. Is that good enough? What is the relationship between the mm the laser dot is off centre of the primary or the centre of eyepiece, and drop-off in viewing quality - rapid, slow??
My second question is about the mechanics. The mechanical design of the primary adjustment, I think I understand. It seems to me that I can adjust the three collimation screws independently - ie. I don't have to screw the other two out to compensate for having screwed one in (unless I was really worried about my focal length to the nearest mm or fraction thereof?? On thinking about it, any change in distance of the primary mirror from the secondary is probably compensated for in the focuser?). But I don't understand the mechanical design of the secondary (we are talking about a Bintel premium 8" reflector, vintage Nov 2006). I will pull it apart at some stage to get rid of the screws (replace them with threads with wingnuts I can operate by hand - yes, I may have to "soup up" the dust cap by adding a raised section to accommodate ;)) but, in the meantime, do I need to move the three screws in conjunction with each other, rather than independent of each other? Will I bend or break something if I didn't move them together? I notice that they are relatively tight to adjust, which concerns me a little. Tight enough so that, as I turn them, the spider flexes then relaxes - I don't like that at all.
Thanks for your help. :)