5.7Meters FL: 18" CC on a 1200 mount

Jul 19, 2008



#22436 Jul 19, 2008

I had a short 2 hour window of opportunity to image last night and picked the Crescent. I was hoping for more time but two hours is all I got before the marine layer blew in from SF Bay

Using the 18" f/12.6 classical cassegrain w/o reducer or corrector and a Proline 09000 with its 36.8 x 36.8mm sensor, I took 6 exposures of 20 minutes through a Baader 50 x 50 mm square Halpha filter under a full moon. With the 12 x 12 micron pixels of the KAF09000 and the 5760 mm focal length the image scale worked out to be 0.43 arc-sec/pixel.

Guiding was via an ST7 used on a Lumicon Giant Easy Guider


I measured 2.6" FWHM in my better stars in the images: these were well away from the center too. In tretrospect I probably should have imaged this with 2x2 binning

The 1200 had no PEM on or any software assistance other than straight up guiding via Maxim DL.

That old fall 2000 vintage 1200 just tracks marvelously, even with a load that requires 6 of the 18# counterweights and a shaft extension :-)

I imagine if I had installed Pempro it would work even better.

Then on the weekend before with the identical setup, I got a "clear" night with good seeing. I qualify clear because the skies had a lot of smoke in them from the well-publicized wildfires all around northern California, so the extinction was running high.

But here is SH2-112 imaged at 0.43"/pixel with 20 minute subs. The FWHM of the stars measured between 2.1 and 2.3" that night. Total exposure was 3h 20m


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