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Hi folks.
My 6 inch f3.6 SN is very touchy re collimation. Its primamry is fixed, and so then only means of adjustment is in the secondary. It has a metal pin in the holder to stop it spinning when I adjust the screws. Ive found a standard laser collimator isnt too bad, just adjust till laser lands on centre spot on primary. However I stil get an odd effect, stars in the top left of the field tend to be out of focus but elsewhere not too bad. This effect is far worse without the MPCC. Another odd phenomenon, when I collimate using star testing, if I use an eyepiece (4.7mm Nagler) the star will look good with even diffraction rings, but if I use my 2,8x Barlow star looks uneven, if I then adjust so it looks good, it then is out when looking without the barlow.
I once used a mates hi tech grid laser collimator that projects a grid, allowing one to check for everything even for an out or parrallel focuser, but on my SN I got all these wierd reflections I couldnt interpret at all. So it seems that SN's at least can be an odd thing to collimate.
For a normal Newtonian I just recoment adjusting the secondary and primarywith a laser collimator, if really fussy can tweak primary with star testing, rack focuser out past focus till u get the donut, adjust primary till "hole" is dead centre, using a medium to high power eyepiece.
Scott
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