Re: Atmospheric Refraction, Tracking Accuracy and PulseGuide

Dr. David Toth

At 02:16 PM 4/4/2008, Ray Gralak wrote:

TPoint (and software like it) only corrects position when the telescope does
a slew. When tracking there is also an instantaneous rate change in RA and
Dec whenever there is flexure, which is always present to some extent when
you have gravity.

So you can disagree all you want but flexure is a factor in dynamic tracking
rate calculations.
You are absolutely correct Ray (but you knew that!) and TPoint can model that rate change (and you knew that too).
As Roland and Ray point out, the big payoff comes when trying to guide thru narrow-band filters where you may use a 45-60 second guide-star exposure. You need to be able to have the mount track well on its own for at least 1-2 minutes. This may not be problematic for a short focal length refractor, but at longer focal lengths, this can be quite a feat for a mount. While you CAN use a separate guide scope, as Roland (and others) points out, you can get differential flexure .... of course, you could always model that out too, but that is a heck of a lot of math and computer power.


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