From: Mark Gaffney <markgaffney@mac.com>
Date: August 12, 2008 1:12:14 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: Autoguiding...
Hi Milton, How do you manage with such short exposures on the Unibrain. Is that sufficient to give an analysis of the sky when guiding. I remembered I`d previously had some success with Iterative Polar Alignment in Astroplanner. About a week ago or so I tried again & was getting a 1 degree error after a first run through (after adjusting the mount controls). Since then I`ve shifted the tube to better align the finder scope. I found I didn`t have the correct o-ring for it & that by shifting the dovetail mount & rings I`ve got an alignment on a fence post during daytime anyway & more play with the screws. Because I`ve been experimenting with the camera on the 4" & also because it`s quite cold here at present I haven`t made any advances. Here`s a link to Jeff Phillips site. He`s using a Macbook ( I suspect Intel), PhD & the Orion Short Tube 80 guide scope on his 10" meade refractor.<http://imjeffp.blogspot.com/2008/07/m27-dumbbell-nebula-again.html> Mark.
On Tuesday, August 12, 2008, at 09:51AM, "Milton Aupperle" <milton@outcastsoft.com> wrote:
--- In Astro_IIDC@yahoogroups.com, Mark Gaffney <markgaffney@...> wrote:
Hi Milton, I`ve just written to Frank from the Autoguiding Yahoo
group about guiding using the set-up I had in mind with the Orion
Short Tube 80 Guidescope & Astro IIDC. Here is what he said in part;
"As for guiding the big C10, I expect the mirror will cause flexure
problems, so be prepared to see oblong stars at long exposure. But if
you keep exposures to 1-4 minutes, and depending on where in the sky
you are imaging, it may work ok."
I think Frank (FreeStar8) is under the impression your C10 is a CAT
scope, which means the mirror slides up and down on the greased baffle
/ shaft through he center of the mirror. The only reason you would
have mirror movement in a Newtonian is if the mirror isn't securely
held in the mirror cell.
Also with respect to using the Unibrain Fire-i webcam as a guide
camera; "I guess that camera uses a Sony CCD. It looks like it is
uncompressed
color camera? The color isn't ideal for guiding, but non-compressed
will help." To your knowledge is the Unibrain a non-compressed
camera? He says also that PhD has a Mac version. How does it stack up
against Astro IIDC for guiding in your opinion? Mark.
The Unibrain's are uncompressed, however the longest exposure it can
do is 1 second. With an 80 mm guide scope scope the best your going to
reach is maybe mag 6 or 7 guide stars (this has been discussed at
length about in the past in the archives of this group too).
And I've never tested PhD because it won't display video with any of
the dozen or so FireWire Mono / Color cameras I have here or on any
Mac with 10.4.x or higher. If I can't use the camera in doors from my
desk, there is no point trying it on a telescope, so that's as far as
I got with it.
Lastly, until you solve your pointing / alignment issues with the 10"
Newtonian and it's mount, your wasting your time trying to guide with
any product. Without accurate polar alignment, you will be come very
frustrated with any product trying to guide with it. It simply isn't
going to work reliably.
HTH..
Milton Aupperle
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