Re: [APML] 500mm mirror lens as a guidescope?

[George Anderson <georgea@cam.org>]

Hi Derek

The lateral shift will be more of a concern as it will move the
guidestar about. The focus will hopefully not be a crucial issue, that I
can checkout easily in the front yard and see if it shifts over a 1 hour
time period.

George

DEREK BAKER wrote:
> 
> I have heard stories of the lens elements shifting over long exposures, both
> laterally, and in terms of focus. If your shots were just 10 or 20min,
> then....
> 
> Derek
> 
> ----- Original Message -----
> From: George Anderson <georgea@cam.org>
> To: APML <astro-photo@seds.org>
> Sent: Tuesday, September 02, 2003 10:57 PM
> Subject: [APML] 500mm mirror lens as a guidescope?
> 
> > While messing around with getting my B&W quickcam autoguider working and
> > starting to worry about focuser flexure on my el-cheepo guidescope I
> > started wondering (dangerous habit)...
> > For widefield shots with a 35mm camera (50mm lens or less) would a
> > guidescope with a 500mm focal length be sufficient?
> > The 500mm f/8 mirror lens I have is very lightweight and has no
> > detectable barrel flexure. The effective aperture is only 62mm but that
> > is only a touch smaller than my 70mm f/10 scope that I use for manual
> > guiding.
> > Any thoughts from those in the know?
> >
> > George Anderson
> > Montreal Canada
> >
> > Clear skies and good health
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