>
> Bert:
> I don't think that the laser is the way to collimate a Schmidt Cassegrain.
> I've been collimating my refractors with it. I collimated the my C5+ SCT,
> with the laser, basically centering the dual image seen in the tube. Easy to
> do but when I tested on a star image, I had to re-collimate using star
> diffraction rings, which is probably the best way for a SCT. In Howies write
> up for SCT he also notes that sometimes after collimation your image might be
> worse for a SCT because of probably "other aberrations elsewhere in the
> system being compensated out by tipping the scondary...... I think he is
> right.
>
> I did did however discover some important things, those diagonals can be way
> off!! All three of mine were quite off. The projected laser beam was off
> 1/2" from center on the objective of an 80mm (this is after I had alighen the
> focuser which was also off). The focuser was also off quite a bit on my 5"
> APO Meade. Shimmed and readjusted both diagonals and focusers, now
> everything is dead on and has improved image quality in my scopes. Good luck
>
> Ralph G
>
>
Ralph,

I tried to use the laser for collimation by placing a white semi opaque
plastic on top of the OTA and got a nice projection of the holographic
grid on it. I then centered the secondary mirror on that grid. When I
startested later, collimation was way off. I guess, you are completly
right about the laser beeing no good for a SC scope; I'll stick to
collimating the oldfashioned way. The only problem is, that seeing at
my site is rarely good enough to see decent diffraction rings. Maybe'
Ill have to use the daytime method.

Bert Mettier

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