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Richard Crisp
February 21st 04, 01:29 PM
Some folks here were interested in the 18" scope I mentioned I was building.
This is based on the CPT18 from Resource International. I am making
modifications to permit it
to be used as a Classical Cassegrain or as a Newtonian, as it was originally
designed.

In Cass mode, it will be f/12.6 using a 3x multiplier for the
secondary. The illuminated field is 49mm, designed to support either
a 35mm negative or one of the new STL11000 cameras from SBIG.

In Newt mode, it will have a focal ratio of f/4.2.

Here are some pix of the frame in the back seat of my wife's car.

www.rdcrisp.darkhorizons.org/images/CPT18_bmw540_1.jpg

www.rdcrisp.darkhorizons.org/images/CPT18_bmw540_2.jpg

The optics are the pacing item, with expected delivery in the
May/June timeframe. I hope to have first light about a week or two
after receiving the optics if all goes well.

It is an aggressive project for sure, but I am optimistic that the
results will match expectations.

if interested in the CPT scopes you can see them at the Resource
International website.

http://astronomy-mall.com/regular/products/cpt/

David Whysong
February 25th 04, 05:49 AM
In sci.astro.ccd-imaging, Richard Crisp > wrote:

> In Cass mode, it will be f/12.6 using a 3x multiplier for the
> secondary. The illuminated field is 49mm, designed to support either
> a 35mm negative or one of the new STL11000 cameras from SBIG.

That's a great idea, but an 18" 'scope with that focal ratio means the
STL11000 pixels subtend only 0.32 arcseconds.

> In Newt mode, it will have a focal ratio of f/4.2.

....which is much more reasonable for 9 micron pixels. Why not use
it for imaging in this configuration with a large coma corrector?
Would that work?

Dave

David Whysong
DWhysong (at) physics (dot) ucsb (dot) edu

Richard Crisp
February 25th 04, 04:30 PM
"David Whysong" > wrote in message
news:[email protected]
> In sci.astro.ccd-imaging, Richard Crisp > wrote:
>
> > In Cass mode, it will be f/12.6 using a 3x multiplier for the
> > secondary. The illuminated field is 49mm, designed to support either
> > a 35mm negative or one of the new STL11000 cameras from SBIG.
>
> That's a great idea, but an 18" 'scope with that focal ratio means the
> STL11000 pixels subtend only 0.32 arcseconds.


You can also bin 2x2 which offers a lot of advantages including image
processing time.


>
> > In Newt mode, it will have a focal ratio of f/4.2.
>
> ...which is much more reasonable for 9 micron pixels. Why not use
> it for imaging in this configuration with a large coma corrector?
> Would that work?

just might, Dave.

I have lots of options as to how I instrument it.