I was aware that collimation was important with SCT's, but I
never realized how important until recently. I'd been
struggling to get proper focus and accurate tracking in
order to get good round small well defined stars on my
astrophotos, and I just wasn't getting the results I was
hoping for. In other words, I hadn't taken care of first
things first. I'd done a text book (Meade manual)
collimation a while ago, but what prompted me to check again
was a chance photo (digital) of a bright but very unfocussed
star. Out came the big classic doughnut, and there it
clearly showed the off center "hole". That's when I also
discovered that using a photograph rather than a diagonal
and eyepiece was easier, and more precise. For one thing,
eyeballing that doughnut and judging whether it's properly
centered is a judgment call that leaves me wondering if it
really is as centered as it can get. Having a photograph,
and being able to zoom in on it and literally measuring the
pixels when it gets down to the fine points leaves me
feeling a lot more confident that yes, that hole truly IS as
centered as it can get. When I finished collimating this
time, the subsequent astrophotos revealed that I'd been
trying to improve tracking when actually the culprit was
poor collimation. Suddenly, focusing became a lot easier,
and the tracking looked like it had improved dramatically.

I'm a bit new to this, so I'm sure some of you more
experienced ones know this, but I also discovered that the
center of the photograph (or eyepiece view for that matter)
is not necessarily the place where the doughnut should be
examined for proper centering of the hole. Moving the star
to the edges of the photograph caused the hole to be off
center, but triangulation of the direction of the offset
aided in determining the true center of the field of view, -
where the doughnut should be set and checked. Again, it was
a lot easier to do this with a photograph where I could more
easily triangulate, and then definitively place the doughnut
at intersection X and Y.

I maybe should mention at this point that I was using a
digital camera at prime focus that downloads photographs to
my computer where they can be easily examined. I don't have
an illuminated reticule eyepiece. I maybe should have been
doing this all along, but now I know to take a quick
"collimation" photo check before getting down to business.

I did a search for "Collimation" and it brings up a number
of good articles. One thing was clear in most of them, the
instructions in the Meade manual are not all there is to the
story. Although a necessary first step, is actually more
like a rough collimation. There is a lot more to a very fine
collimation, and a fine collimation is one of the necessary
ingredients to get fine results.

Hope this helps someone else out,

Keith
W90N45

My(New!)Astronomy Website
http://www.willowberry.net/keithnk_m42/

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