Re: Collimation?
- From: "Uncle Bob" <realonespam@xxxxxxxxxxxx>
- Date: 25 Nov 2005 20:28:16 -0800
Collimating SCTs is pretty straightforward (star-testing collimation),
but it requires good seeing to achieve maximum benefit. But when you
achieve that benefit, the result is dramatic image improvement. This
is because miscollimation really degrades image quality in SCTs, more
so, imho, than in Newts. I was absolutely delighted the first time I
collimated my C-8 and saw (for the first time) diffraction rings around
a star. When you see those faint, concentric rings (only with good
seeing) you know your planetary detail is going to be top notch. I
haven't had to touch it in two years, btw. The rings are still there.
I have recently acquired a previously-owned (don't ya love that term?)
Intes MN-66 Mak-Newt, and just last night seeing was good enough to
collimate using a defocused star image--not good enough to let me use a
focused star image, though. The rings were in and out, but the
improvement was so dramatic I was floating on air. Very
"refractor-like" images, and wonderful planetary detail, especially
from an f/6 instrument of such modest aperture.
What Rod said about truss-dobs is quite true. I often find myself
reaching for the laser halfway through the evening when I notice stars
growing whiskers, or when I notice planetary images are getting soft.
I guess it has to do with the aluminum truss tubes being very
thermal-expansive. Usually, it only requires a quick tweak of one
primary screw to bring things back.
Good luck to you with your choice and clear skies!
Uncle Bob
.
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