Measuring periodic error?

Greetings.

I saw the thread about CG5 mounts and the link to the french site
that compared various mounts. I am wondering how one measures periodic
error, as the nice french people did on that site.
Is this something one can do easily at home, or does it require a
trip to Sandia Labs?

Regards,
Uncle Bob

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On 21 Aug 2004 21:27:08 GMT, Manuel Joseph Din wrote:

Greetings.

I saw the thread about CG5 mounts and the link to the french site
that compared various mounts. I am wondering how one measures periodic
error, as the nice french people did on that site.
Is this something one can do easily at home, or does it require a
trip to Sandia Labs?

If you have a guider, you can recover this information directly from the guide
log. Otherwise, a simple approach is to misalign your polar axis so you have a
lot of declination drift, and just make a long image. The stars will be trailed,
and you will see a nice sinusoidal motion superimposed on the trails, which is
from PE. By measuring the peak to peak deviation (obviously, you need to know
your pixel scale) you can accurately determine the PE.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On 21 Aug 2004 21:27:08 GMT, Manuel Joseph Din wrote:


Greetings.

I saw the thread about CG5 mounts and the link to the french site
that compared various mounts. I am wondering how one measures periodic
error, as the nice french people did on that site.
Is this something one can do easily at home, or does it require a
trip to Sandia Labs?


If you have a guider, you can recover this information directly from the guide
log. Otherwise, a simple approach is to misalign your polar axis so you have a
lot of declination drift, and just make a long image. The stars will be trailed,
and you will see a nice sinusoidal motion superimposed on the trails, which is
from PE. By measuring the peak to peak deviation (obviously, you need to know
your pixel scale) you can accurately determine the PE.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Gee, thanks, Chris. I appreciate your taking the time to explain that.
Regards,
Uncle Bob

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Chris

Thanks for this - I have wondered whether it was measured peak to peak or
plus/minus. It is never specified....

Adam

"Chris L Peterson" wrote in message
news
On 21 Aug 2004 21:27:08 GMT, Manuel Joseph Din wrote:

Greetings.

I saw the thread about CG5 mounts and the link to the french site
that compared various mounts. I am wondering how one measures periodic
error, as the nice french people did on that site.
Is this something one can do easily at home, or does it require a
trip to Sandia Labs?

If you have a guider, you can recover this information directly from the guide
log. Otherwise, a simple approach is to misalign your polar axis so you have a
lot of declination drift, and just make a long image. The stars will be
trailed,
and you will see a nice sinusoidal motion superimposed on the trails, which is
from PE. By measuring the peak to peak deviation (obviously, you need to know
your pixel scale) you can accurately determine the PE.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Tue, 24 Aug 2004 16:46:43 +0100, "Ado"
wrote:

Chris

Thanks for this - I have wondered whether it was measured peak to peak or
plus/minus. It is never specified....

Adam

What you care about is peak to peak, since that is what shows up on an image.
Usually, that is how it is specified, although I have occasionally seen it given
plus/minus. If you are looking at someone else's spec, and it doesn't say, you
have no way of knowing for sure what they are actually measuring.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com