Re: [APML] Backlash query

["Bobby Middleton" <bobm@koyote.com>]

Ian, I'm not familiar with Vixen drives, but if the backlash is only in DEC
then you can defeat this with manual guiding. You'll want to get well polar
aligned but you will still wind up with a small amount of drift in DEC. But
it will be in only one direction. Know which way the drift is and never
correct the other way. That way the backlash will never come up because you
will only correct in one direction. I did this for up to 90 min manual
exposures on a sloppy LX200 drive with a problem more severe than DEC
backlash. I had DEC retrograde motion which actually made the mount track
for an instant the wrong way before it began correction the desired
direction. I sloved my problem with a DEC bearing mod but the strategy
worked until then. Now if you have a drive with RA backlash then you're
probably pretty much sunk on getting a fix for that.
Bobby Midleton


http://www.koyote.com/users/bobm/word.htm

----- Original Message -----
From: I.J Jordan <Ian@sun-house.demon.co.uk>
To: <astro-photo@seds.org>
Sent: Sunday, April 09, 2000 4:06 PM
Subject: [APML] Backlash query


> Hi Everyone
>
> I was reading a few day ago a short thread regarding the backlash in Vixen
> drives compared with the drives with the Skysensor 2000.It raised a
question
> in my mind that someone may be kind enough to answer for me.
> The question being:at what point does backlash become a problem.I am
> wondering because although I would aspire to create images like I see on
the
> various websites belonging to members of the mailing list,I know that I
have
> to be realistic and say that it would be a long while before I could
afford
> autoguiders big heavy mounts etc,so what I am interested in finding out
> given that I have a "fast" scope (10" f4.8) would backlash become a
problem
> in for example a number of short exposures (all things being equal,and
> ignoring for the moment all the other problems that can crop up),of say
> 15-20 minutes and stacked in the computer.My gut feelings tell me that
> perhaps it would only be a problem if the OTA crosses to the other side of
> the mount during the exposure,but I will certainly stand correcting on
that.
>
> Thanks for any thoughts.Clear skies
>
> Ian & Linda Jordan.
>
>
>
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