Re: [APML] st4 dessicant-ring, find&focus

["Jim Janusz" <jjanusz@ix.netcom.com>]

Hi Joe.........


----- Original Message -----
From: "Joe Durant" <ccd43@hotmail.com>
To: <astro-photo@seds.org>
Sent: Monday, May 28, 2001 10:38 AM
Subject: [APML] st4 dessicant-ring, find&focus


> What are the symptons for dessicant ring renewal?

Ice on the chip ot window..........

>
> I did some Find&Focus tests, & the reading was jumping around.  17 21 25
18
> 19.  I never saw this before.  2 nights ago, there were high thin clouds.
> (that's the explanation.  the numbers were fluctuating like wild)  1 week
> ago, I was at a slightly lightpolluted site, I'm sure there were no high
> clouds, I was still getting the unstable #'s.  The skybackground wasn't
> causing it, was it?
>

Unstable numbers are usually caused by either short exposure times or bad
seeing, they are not that unusual IMO.


> I read Jim Janusz article on ST4 focus.  How many people really adjust
> focus, depending on what part of sky your autoguiding on?
>
> He also states the ST4 likes faint guide stars. (value ~15) Suppose you
get
> a reading of 54 with EA=1.0.  Would I gain anything, by setting EA=.3, to
> get the reading around 15?  (then setting AA=3)  Would that lead to more
> accurate centroid calculations, & better guiding?

My statement about faint stars was meant to convey the idea of a very stable
brightest area for the centroid calculation.  Faint stars requiring longer
exposure times will often lead to very accurate guiding because the seeing
gets averaged out.  A similar result can be obtained with bright stars by
averageing.  I typically try for a setting of around 25, if this requires a
short exposure I will average if it requires a longer exposure (3 to 5
seconds) I go with an average setting of one.


>
> How many people calibrate at a certain speed, then guide at a lower speed?
> The reasoning is to lower feedback (more dampening), to lessen oscillation
> (overshoot).  I tried this once with the Takahashi EM100, & I could tell
by
> the numbers that it took 2-3 cycles to correct for the RA error.  So, I
set
> it back to the rate (at which I calibrated at).

I don't, but I think this is very dependant on the mount being used.  My GM
200 likes the two lower speeds, both work as well but I usually use .2x.

Jim


>
>
> Joe
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