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Subject: [M]: RE: centering an image on a CCD
From: Michael Hart
Reply To: mapug@shore.net
Date: Fri Feb 27 00:00:48 1998

On Thursday, February 26, 1998 11:07 AM, jordanp@cheyenne.com wrote:

> hi. just got my 216xt and as most beginners experice, the ccd's
> field-of-view is very narrow. can anybody recommend an easy way to center
> an object on to the ccd ? besides an expensive flip mirror ?
>
> i've created a parfocal eyepice and it kinda works for daytime images.
> when you substitute the ccd imager in place of the eyepice, does the CCD
> 'see' what ever was at the center of the eyepiece ?
>
> thanks.
>
> jordan
> jordanp@cheyenne.com
>
>
>

On Doc G's Website, http://www.mailbag.com/users/ragreiner/index.html
under CCD Imagers and Accessories, Color Imaging Methods with the
CCD Imager, Tips for Tricolor imaging- I describe using the finderscope
to place an object on the CCD chip. I recommend a standard illuminated
reticle type, though at the recent WSP, a CCD imager whom I was helping
used a standard Meade finderscope and a red flashlight to illuminate the
crosshairs due to the darker sky background. In this case, he was using
a large CCD chip, however, I have used the illuminated reticle finder with
for chips of the 216 class.

The procedure is to use the HPP mode and center the star in the finderscope
and finish your slew to the object. In my case, the object is quite near the
chip center. Take 5-10 second continuous binned exposures using the Guide
Mode (in my case, the Center Mode) to move the object which will precisely
center the object of interest on the CCD chip. Practice and experience
makes this very automatic and extremely time efficient while maintaining
CCD camera focus (the camera is never removed).

Others prefer flip mirrors and even more expensive multi-port devices. However,
I personally prefer to let the telescope do the work and not use these items
which aides in eliminating backfocus problems, light leakage, flexure, camera
hitting the base, internal reflections and extra expense. I am a firm believer in
perfecting techniques (including manually guiding) before buying accessories
that can complicate your setup, increase the learning curve and later become
unnecessary with experience.




--
Michael Hart
Husen Observatory
mhart@netexpress.net