[APML]: New Pixs

[Steve Bell <sb635@delphi.com>]

I finally got a few new photos: the Horsehead, and the galaxies M51 and
M81. The reason why I haven't posted new images has been because I've
been working on my autoguiding. I tried all kinds of combos of PEC
autoguiding training exposures, coupled with various actual guidance
exposures, but what I decided was the best was no PEC, but slightly
adjust the overall tracking rate to about 59.9 Hz and then use a 5 sec
guidance exposure. My scope has always tracked a little too fast to the
west when running at 60 Hz, and the 59.9 Hz setting effectively
eliminates the slightly too fast westward movement. With this setting, I
can not also run the PEC on my JMI MT V drive corrector, but I don't
think I want to use it anyway. It appears that there is a good deal of
worth to using relatively long guidance exposures if your seeing is
generally not too good, like mine. I'm now convinced that with exposures
of shorter than 3 secs, my scope actually chases the seeing too much and
causes unacceptable trailing.  With a longer guidance exposure, the
seeing movement of the guide star on the CCD chip averages itself out
during the long exposure, and the scope doesn't chase the seeing as
much. And with my scope, it appears that longer than 5 secs and it
doesn't take out enough of my drive's periodic error. On the M51 and M81
shots, I used a 7 sec guidance exposure, and there is a slight bit of
trailing evident. The Horsehead shot was done with 5 secs, and it is
pretty well guided. 

Of course, if you are imaging under these conditions, you can't really
expect great resolution, as my shots certainly prove. I guess I
shouldn't expect great shots because of my generally poor seeing,
coupled with the fact that I image from a metropolitan area with 2
million-plus people. I was fairly pleased with the Horsehead shot,
especially since during these nights, the humidity was very high for
here in Denver (90% +) and it was pretty cold (in the teens) and I had a
devil of a time keeping frost from forming on all the glass surfaces. In
fact, by the end of each night, my scope had more than a 1/8" layer of
frost formed on the old 16"'s Sonotube. I'm finding, when it comes to
galaxies, that I probably just won't be able to adequately record any
whose mags are about 9 (or dimmer) from my city location. Even with
filters, I can only expose about 75 mins at f/4.7, even using moderately
under-hypered TP, before sky fog becomes a major problem. Without a
filter, I can only go about 20 mins, and these exposures are just too
short to record dim galaxies, even at f/4.7. Oh well, there are plenty
of other things to shoot besides galaxies. I am amazed, though, that I
can record any galaxies at all (that are millions of light years away)
from such a big city as Denver. That is, on film. I have a feeling that
the best way to record galaxies from a city location is to use a nice
CCD camera, like an ST-7 or 8. Of course, the very best thing is to get
your butt out to a dark site with good seeing!

BTW, these new shots were done using Orion's SkyGlow filter, which I
find to be every bit as good as Lumicon's DeepSky filter. Also, there
was some discussion a little while back about how sometimes you can get
round star images on one part of the frame while there are elongated
star images on other parts. I myself have had this problem, but I've
eliminated a lot of it by drilling and tapping a third set screw for the
port that holds my 35mm camera. With only one or two set screws, when
you tighten them down, the camera tilts a little, and apparently at the
short f/ratios of below 5, the film needs to be held fairly precisely at
a right angle to the incoming light cone, or else elongated star images
will form on locations of the frame where you haven't purposefully
focused (I always focus on the center). With three set screws, you can
alternately tighten each one down a little at a time, and the camera
stays more right-angle oriented.

-- 
Clear skies,
Steve Bell
email: sb635@delphi.com
Astrophoto page: http://www.mindspring.com/~sb635