Re: [APML]: Measuring periodic errror

[Kevin McGoohan <kpm6@worldnet.att.net>]

The Astro-Photography Mailing List
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>> Most people consider periodic error to be an RA only error.  But an error
>> along the Dec. axis can be just as dangerous.  The quick, 3-4 second, error
>> burst is the real danger.  An auto guider can't keep up with it and if you
>> are manually guiding you can't relax at the eyepiece.

>Er, ummm... On an equatorial mount the periodic error *is* only
>on the RA axis. 

That is the convention and that is what people usually are talking about
when they refer to periodic error.  One of my old mounts had a Dec component
to its periodic error.  Just as the RA component was +/- 2 arcmin the Dec
component was about +/- 1/2 arcmin.  The Dec component was just as real as
the RA component and had to be guided out.  This was a very poorly made
mount by the way.

Kevin <kpm6@worldnet.att.net>