Re: [APML]: Astro mount advice

["Paul Sterngold" <psterngold@hotmail.com>]

>The Vixen SP mount is quite good.  RA corrections I do about every 3 to 
5
>mins, and dec I can leave untouched for well over 15 mins (setted up 
using
>the polar finder scope)  That's when you want to keep the guidestart 
in, or
>at the edge of, a 9mm Meade doublecrosswire eyepiece (giving 133x magn 
on
>my 1200mm f.l. refractor). 1h exposures are unlikely to be guided well,
>unless you use lenses < 50mm.
>
>Piggybacking is best done on the counterweight axis : this way your 
mount
>is less stressed.  Balancing is not that important. An unbalanced RA 
axis
>can even squeeze the gears a little tighter so they respond better.
>
>For $800 you should have no problem finding the mount and dual axis 
drive
>(imperative - the manual dec slow motion control is way too coarse for
>anything above 300 mm).  And some time ago (I guess it was in 1992, 
when
>the dollar was incredibly low), they sold the SP-mount and a 4"  
f=1000mm
>achromat refractor for about 36.900 BEF (no drives included :-(, that 
must
>have been something like £650 back then, so if you can get one of those
>second hand, you should be able to bargain for a good price.
>
>Good hunting,
>
>Jan Saver
>
>P.S. Feel free to mail me back, there is plenty more to tell about
>astrophotography with the SP mount.

I own a Vixen Super Polaris DX mount, and IMHO it is so superior to the 
SP mount that I would recommend it well over the SP mount.  The hardwood 
legs are about double the width of those on the SP mount, and the 
vibration damping time is about 1-2 seconds.  Also, the fine adjustment 
for altitude is much better.  I used to get quite frustrated with my SP 
mount, because I would get Polaris perfectly aligned in the polar scope, 
then tighten the locking thumbscrew, and the mount would shift!  The DX 
version uses a different design that is more rigid and also doesn't 
shift when tightened down

I bought mine used with d/a drives, hand paddle with 2x and 8x rates, 
SkySensor 3 computer and heavy duty soft case for the mount, for US$900 
from an ad in The Starry Messenger.

I have taken astrophotos up to 45 minutes using my Genesis (f.l. = 
500mm) and they seem well guided.  I use an 80mm refractor with 12.5mm 
MicroGuide eyepiece and a 2x barlow, providing more than adequate 
guiding magnification at 146x for the Genesis.  I mount the guidescope 
and Genesis side-by-side on a 3/4" plywood saddle I made.  The DX mount 
handles all this weight without problem.

I have to admit to more periodic error than Jan mentions in his message.  
I occasionally (I haven't measured the periodicity) find the guide star 
drifting in r/a appreciably, so I keep my eye pretty much glued to the 
guidescope eyepiece and correct about every ten seconds or so.  That's 
just a guess, but it seems nearly constant! <g>

Good luck finding the right mount.

Regards,
Paul Sterngold

___________________________________________
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