University Lowbrow Astronomers

First Run with an ST7

by Brian Close, T. N.
Printed in Reflections: July, 2005.

I recently acquired a used ST7 for $550 and an Astrophysics AP800 mount for $2500. Both good deals.

The AP800 is rock solid and more than enough to carry both my 5” f/4.5 RFT and 6” f/6.5 telescopes at the same time. Both scopes have good mirrors completed at the Adler Optical Shop in Chicago.

Right now I’ve just put the 5” RFT on it and started imaging. Here are some of my first attempts. These shots were from my backyard in Bozeman, Montana. While you can see the Milky Way in Bozeman, I have a security light as a neighbor which reflects off of the trees in my yard. My one difficulty has not been tracking or balance but focusing! My current focuser, a cheapo helical focuser, really doesn’t have the precision to get the stars below the 2.0 Full-Width-Half-Max that they should be. I’m upgrading to a Feathertouch if Tom ever gets the bases he promised me done.

The images are generally 30 minutes total, made of fifteen 120-second stacked exposures, except for the heart of M31, which is 30 minutes of thirty 60-seconds stacked. Acquisition was with MaxIm DL, with calibration darks but no flats (will try t-shirt flats next). After stacking, calibration, and light pollution gradient adjusting, I’m using old Photoshop 5.0 for processing which is more intuitive, if less scientific, than MaxIM. (See Ron Wodaski’s The New CCD; his website is excellent too: MaxIm 4.0 does have some nice features, such as correcting for light pollution gradients, but I’m not prepared to shell out $500 bucks after my demo time runs out. SBIG’s CCD Soft is available to SBIG camera users (with a valid SBIG serial number) for $99 and has similar features. Otherwise it’s $349.

Bottom line, even with an old ST7 without anti-blooming you can have some fun with imaging. Mine cost me $550 and I’ll keep it as a guider when I upgrade to a more expensive camera. I’ve seen ST7Es on Astromart for around $800. My small scope helps, as it really puts no burden on the mount and I can still do deep sky shots with it. My set-up is easy to use and I’ll get a couple of years of play out of it before I get bored again and trade up to something else. (Or 10 years if I wait for Tom to finish my 12” f/6 project!)

Tom, Brian and Jack

Brian, the guy in the center and a true Telescope Nut if ever there was one (and tax attorney), is happy to answer questions, when he’s not swindling widows or kicking small dogs.


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