At 05:44 PM 12/1/98 -0500, you wrote:
>Robert:
>
> I think alot of people are having this problem. I know I was, until I
>tried doing the fork arm alignment that was detailed here some time ago. I
>was also having trouble with inaccurate GOTO's. The fork arm alignment
>completley eliminated the problems. The problem appears to be that the OTA
>is not properly aligned with the fork arms and the mechanical RA and DEC
>axis. The adjustment is probably detailed in the archives and is a bit
>finikey. I have refined the procedure a bit to be as follows:

[a bit of brilliance snipped]

What a great idea! I have examined an oblique reflection off the
corrector.... stationary reflection as the OTA is rotated was used to
determine if the OTA was aimed parallel to the RA axis. But your method
also takes into account the actual optical axis, which as you say is not
necessarily exactly coincident with the mechanical axis.

A refinement just occurred to me. Your method assumes the fork arms are
exactly paralell with the RA axis. If they are not, there can be some
error. What about this slight revision....

Place a white cardboard on the base over the RA axis as in your method,
attached to the RA bolt so that it does NOT move when the scope is moved in
RA. Concentric circles on the cardboard will help here too.

Now, rotate the scope in RA only. Adjust the DEC and the OTA adjustment
screws (and the fork arms if needed) so that as the scope is rotated in RA
there is no motion of the light cone on the stationary screen.

As far as I can visualize, the only way the image of the light cone can be
stationary on the stationary screen as the scope rotates in RA is if the
optical axis and the fork arms are precisely parallel to the RA axis.
Keeping the scope pointed near vertical should eliminate flexure from the
equation.

Whatcha think?



Paul Goelz
Rochester Hills, MI
pgoelz at eaglequest dot com

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