On Monday, June 15, 1998 4:00 AM, Nigel Puttick wrote:

> Philip Perkins wrote:
> > Early this year I trained my PEC using the ST-4 set to .5 second exposure
> time. It seemed to go well and initially the training seemed to be quite
> good... But when examining the images under very high magnification in
> Photoshop I wasn't happy with the amount of RA trailing.<
>
> For those of us who would like to *try* training the PEC using an
> autoguider, could Philip or Michael (Hart) describe the technique in
> detail, please? It isn't immediately obvious; for example, should you set
> the autoguider guiding before invoking the SMART command, so that it is
> already running and issuing corrections, or when the display gets to "5",
> or after, or...? Also, would it be worth training with the autoguider
> first, then doing a manual update? Or perhaps vice versa? Should I assume
> the guider would be best placed at prime focus?

You use the autoguider similar to manually training the Smart Drive.
Start out with the autoguider making guiding corrections BEFORE
the Learn display counts down to "0", which corresponds to the
beginning of the 8 minute worm period. Since the autoguider
doesn't get fatigued, you can start it well before engaging the Learn
process to determine if excessive guiding corrections are invoked.

I am still trying to find a dependable method to get an autoguider
to out-perform the human for a short time period under typical
4 arc second seeing. Then, we need a minimum of 1 autoguider
correction per second for good sampling of the 2 second record
period. The ST-7 is limited to 1 correction per 1.45 seconds at
a 0.11 second exposure, variable with different camera control
software. As a result, I believe the ST-7 is marginally able (do to
software overhead) to program the smart drive even under excellent
seeing. I don't believe there is a published ST-4 correction rate,
so I will need to test this as well.

If the autoguider is better than the human, I would use the autoguider
for the Learn and Update. If the human is better, I would use the
human for both the Learn and Update.

All my tests were with the autoguider on the imaging scope at
around 1500-2000 mm focal length using various focal reducers
on 12". This focal length seems to produce the most accurate
guiding, regardless of a longer imaging scope focal length.


> I have an ST4, which I have been unable to use due to the very frustrating
> UK weather so far this year, but would expect any advice to apply to the
> 201XT as well, so I think this would be useful advice.
>
> Hoping you get my *drift* ...
> Thanks
> Nigel Puttick
>


--
Michael Hart
Husen Observatory

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