> I ordered the "Optec" f/3.3 focal reducer for my 10" LX200 f/10 on Thurs. 8/27/98.
> It's quite an expensive bugger ($350 + $50 for camera adopter). ***** WOW *****
> I don't have it yet, but from what I have read on this forum, and my calculations, it
> seems to be a good solution to achieving about 2 seconds of arc per pixel on my MX5-C
> CCD camera. (I think it will actually give me about 2.4 seconds of arc at 2540mm
> focal length and a CCD pixel size of 9.7 microns).

Expect to loose some resolution with this reducer. I have measured a point
spread increase of (measured at 1/2 the stars maximum intensity point)
from f/10 to f3.3 with the Wratten filter. Stars that are just separated at f/10
will appear a little bloated and will touch at f/3.3. With your smaller imaging
chip, flat fielding may be optional. Not so with the KAF-0400- there is a light
fall-off of 21% which is noticeable in many images.


> Ok here is my question:
>
> I am dedicated to flip mirrors to center and focus my CCD camera (spoiled). With the f/6.3
> focal reducers, with their -130mm focal length, this is no problem. With the f/3.3
> "Optec" unit with it's -29.7mm focal length, a flip mirror is out of the question.
> I must rely on the slew precision of the LX200 and focus by trial and error.

Use the finderscope for rough centering, then finish with the CCD camera.
Use a Hartmann mask for focussing- it's more precise than your flip mirror/
eyepiece. You can use the diffraction method to check focus until your
focusing skills are better with the Hartmann mask.


> Can anybody give me suggestions on using the "Optec" unit?
>
> I realize that I will have 3 times the FOV on the CCD with the "Optec", but even that
> is not enough if you can't actually see an object through a flip mirror.

The Kodak KAF-0400 chips binned to 18 micron pixels will show just about
any popular object in a 10 to 30 second image. Perhaps the MX5-C will as
well.


> Also "Optec" says that their reducer is corrected from 5000 - 9000 microns and a
> yellow filter is suggested to cut out the blue below 4000 microns, which will be out of
> focus. How can I use a yellow filter when my CCD camera is a one-shot-color unit, won't my
> pictures look yellow?

Not exactly. If your CCD chip recorded light with photometric accuracy, your
images would be almost absent of blue. Grays would look yellow, but blues
will look green- increasing the green record considerably. The Wratten #12 filter
passes colors longer than around 480 nm (green and red wavelengths) while
absorbing most of the blue wavelengths. I believe you may have to forget the
yellow filter with your color chip and live with the aberrations.

However, the Cyan and Magenta filters on the MX5-C Sony camcorder chip are
not photometric. They are optimized for visual use in a camcorder so that you
will likely see non-photometric blue (really blue-green) in your combined color
image. This is how your chip produces so good a blue record- because it is
really recording longer wavelengths and mapping them to blue.

The SBIG filters are also optimized to "help" with the blue record. Unfortunately
a gap in the crossover between red and blue channels in the SBIG filters prevents
recording much of the sodium emissions and leakage (too much crossover)
between the green and blue channels almost doubles the light recorded at the
crossover points. The use of a MacBeth Color Checker will verify the accuracy
of your chip, CMY plus G filters, and color model implemented in your software.
However very narrow, but important emission lines desirable for astronomical
images are a small a part of a typical terrestrial image, so very close examination
of MacBeth colors is required.



> Any suggestions greatly appreciated.
>
> Chris Frye
> Silver Spring, MD
>


--
Michael Hart
Husen Observatory

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