[FedCom] First light testing of new homemade 18" Collapsible Classical Cassegrain

[Richard Crisp]

Last fall I kicked off the design of an 18" collapsible convertible cassegrain/newtonian scope. After waiting for nearly 9 months for all the parts to arrive, I was able to finally assemble the scope about 10 days ago. Then finally last night the skies cleared enough for me to begin testing it.

I was expecting to have to solve problems first night under the stars and I wasn't disappointed in that regard. The key one was coming up with a method of taking flats. Normally I shoot my flats in the daytime and with an open frame such as I have with the 18" cass I expected that would cause me some problems.

One thing that has been identified as an issue is the fact that my baffling permits "Flooding" of light past the secondary baffle to shine directly down the primary baffle. That causes lots of problems including shooting flats. That is sort of the next big task for the scope is to correct that. The baffle maker is planning to make me an extension baffle for the secondary mirror and that should cure the problem.

I also had some vignetting due to the way I assembled my beam splitter to permit me to use an AO7 to guide this F=5760mm beast. Once I shot the images last night that was apparent and I believe I corrected the problem today, but the clouds haven't permitted me to test it.

I also made a small baffle to insert into the primary baffle to cut off the flooding rays and it looks like that will at least permit me to take twilight flats, which I was able to do today. Unfortunately as I mentioned, the clouds rolled in shortly after dark so I am unable to test the items I corrected since the images were shot last night.

The first object was the Bubble Nebula, NGC7635. I shot this as a simple RGB. With the 9 micron pixels of the FLI IMG6303E camera used at F=5760mm, I decided to run them binned 2x2 giving me a 4 x speedup in exposure time yet keeping a respectable 0.64 arc-sec/pixel image scale and 1.5Mega pixels of 18 x 18 micron equivalent size.

So this image has the resolution of an ST8E with pixels that are four times the area.

The Bubble was shot as a series of 3 minute exposures, again binned 2x2. That is like taking 12 minute exposures unbinned from a depth of exposure perspective.

The second image was the Trapezium region of M42. This was a series of 15 second RGB exposures and a series of 30 second Halpha exposures. I blended Red and Halpha to use for the Red channel and used the Halpha for the Luminance channel

Because neither image was flat fielded, I have lots of ugly artifacts including dust motes from the optics, some ugly weak columns and other such blemishes that are usually corrected by flat fielding.

The things that I like are that the stars are basically round, and are splitting nicely. The AO7 and beam splitter did a fine job of guiding the AP1200GTO which has a counterweight bar completely full of weights.  That is 6 x 18 lbs + 1 x 25 lbs + 2 x 5 lbs = 143 lbs of counter weights!

Hopefully now that things are more or less ready to test for a second night I will get a chance on Sunday night.

http://www.narrowbandimaging.com/ccc18_first_light_page.htm

or for scope details;

http://www.narrowbandimaging.com/cc18_page.htm