Re: Guiding and Magnification?

From: Dan Mckenna (dmckenna_at_as.arizona.edu)
Date: 03/28/05 

Date: Mon, 28 Mar 2005 13:25:53 -0700

Davoud,

I always used as high a power for visual guiding as I could and some
times a little out of focus to make a disk making the center of the
cross hairs easer to see. One old timer taught me to not to use the
center of the cross but just off to the side as it worked better
with his eyes. It depended on the telescope and cross hair pattern
on how I did it.

Guiding with a ccd one can centroid to better than one pixel in cases
where you have the signal to noise. I usually try to find a guide star
that requires an exposure time over 1 second to reject seeing motion.

Because of the sub pixel resolution one can get with a ccd guider we
have used a focal reducer on the guide camera to widen the field of view
giving us a better chance of finding a guide star.

Dan

Davoud wrote:
> Conventional wisdom once held that the guide 'scope should have a
> greater magnification than the imaging 'scope/lens by a factor of
> (something or other.) With the advent of cameras that contain both
> imaging and guiding chips, or that image and guide using the same chip,
> this notion seems to have fallen by the wayside, and I haven't seen
> this "old rule" mentioned in some time.
>
> This is not an issue if I am imaging with my little Tele Vue 76
> (particularly with the reducer/flatener is in place) while guiding with
> my Meade 8". But what about the opposite situation -- won't it be
> necessary to put a TV "Powermate" or a Barlow in front of the ST-4 when
> it is mounted on the TV 76 and I am imaging with the Meade?
>
> TIA
>
> Davoud
>
> (I don't actually expect to have the opportunity to *use* any knowledge
> that I may gain in response to this post; I have just guaranteed
> another six weeks of clouds in the Mid-Atlantic by taking delivery of
> an ST-4 autoguider that I bought from a gentleman who advertised it on
> AstroMart. Today's weather: flash-flood warning. Tomorrow: worse.)
>

Relevant Pages

  • Re: Guiding and Magnification?
    ... True, but that conventional wisdom was based on visual guiding, not ... >imaging and guiding chips, or that image and guide using the same chip, ... between scope focal lengths that matters, but between pixel scales. ... ST4 probably has large pixels compared with your imaging camera.) ...
    (sci.astro.amateur)
  • Re: guiding relays vs scope controls
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  • Re: Question about this setup
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  • Re: Roll Call (ended up quite long for a young un!)
    ... No Rangers but was a Rainbow Young Leader, then when my Guide Guider went to New Zealand get married my friend and I ran the unit whilst she was away... ... I'm not actually active in Guiding and Scouting at the moment, but keep in touch with my home Guide unit and enjoy SSAGO events. ... I will start Guiding again properly when I live all in one place at a time, and would like to do DofE and Queen's Guide. ...
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    ... > diving right into imaging, but want something that has the potential ... What I like about these mounts is among other things the ability to ... Whether you need guiding or not depends on the focal length and exposure ... you need is a good motor like the MT-1/SD-1 shown, but you will not be able ...
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