thank you for the comment Rashad.
I computed the FOV to be 50 x 33 arc-minutes roughly, using the big KAF6303
sensor (27.9 x 8.5mm active area).
----- Original Message -----
From: "Rashad Al-Mansour" <ramjam@msn.com>
To: <sf-bay-tac@seds.org>
Sent: Sunday, October 31, 2004 9:23 AM
Subject: RE: [TAC] first light testing of 18" Cass
> Hi Richard,
>
> Very nice first light shots. What is the field of view in arch min.?
>
> Rashad
>
> ----Original Message Follows----
> From: "Richard Crisp" <rdcrisp@earthlink.net>
> Reply-To: The Astronomy Connection <sf-bay-tac@seds.org>
> To: "The Astronomy Connection" <sf-bay-tac@seds.org>
> Subject: [TAC] first light testing of 18" Cass
> Date: Sat, 30 Oct 2004 23:42:45 -0700
>
> After completing the initial assembly 10 days ago, last night I finally
> was able to shoot some initial images with the new 18" Cassegrain that
> many of you saw in my foyer at last Saturday night's party
>
> I was expecting to have to solve problems 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.
>
> 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
>
>
Received on Sun Oct 31 10:34:11 2004