Hi Bruce,
Here's something that happened to me not long after I got my SCT8"...
If ever you defocus a star for the purposes of star testing, using,
for example, a 10mm eyepiece, you may not see a perfect star pattern.
It took me a while to notice what "heat plumes" look like. I know you
may think you let your scope cool down, but if ever you get a pattern
that forms a kind of a "V" shape, with the point of the "V" being
close to the center of your "out of focus star" and the two arms of
the "V" being at the outer edges of your "out of focus star", there's
a good chance you may have a heat plume going on.
How would you know? Try the following:
Make sure that with the diagonoal in, your eyepiece is pointing
skyward ( straight up ). If from this angle, the view of the out of
focus star in your eyepiece shows the two arms of the "V" pointing
visually up ( heat rises ), you probably have a heat plume. No amount
of collimation can fix that. However, as you fiddle with collimation,
it seems to improve a bit ( as it is cooling).
Note that your body heat can "reheat" your scope a bit, and cause such
a plume. That happenned to me a few times before it clicked that in
cold conditions, I had to be careful about where I place my body, so
as not to transfer heat to the tube.
Also, temperatures are changing alot between day and night, so unless
the temperature is stable for an hour or two, you have no guarantee
that one hour cooling or even two hour cooling will work. Two hours
"at the same temperature" should cool it though.
Anyway, such a pattern could be some kind of optical aberration, I
guess, but at first impression, it sure sounds alot like a heat plume
to me. I hope that's the case, as that's not much of a problem.
Best of luck with your new scope!
Roland
