Check out:
http://www.isomedia.com/homes/cvedeler/M45t.jpg

This is a 2700 dpi detailed scan (seriously cropped) of the M45 shot on my
webpage. This was a 45 minute exposure with my 10" LX200 using a GEG for it's
focal reduction (f/6.5) but using my guidescope to guide. The mirror cell was
locked down and everything else went right. This is what I am talking about as
far as 45 minutes being the upper limit of exposure time when I use my guide
scope.

>From a web resolution image (http://www.isomedia.com/homes/cvedeler/M45.jpg) it
is not possible to see the oblong stars, but from the detailed 2700 dip scan it
is apparent that the stars are slightly oblong.

Heapy Chris CG wrote:

> An interesting shot Ric, did the object cross the meridian during the
> exposure?
>
> Personally, I use guidescopes exclusively. I have some perfectly tracked
> exposures though of only one hour duration, pity the damn camera wasn't
> focussed correctly - but I have some very sharp donuts!

Without the focus being nearly perfect it would be impossible to see the kind
of error that I (and others) are talking about. I have dozens of "perfectly"
guided donut shots. It was not until I learned how to focus precisely (using a
Sure Sharp) was I able to detect the oblong stars I was getting.

> <snip>
>
> I have never seen the 'failured eposures' that proponents of off-axis guider
> users use to condemn guidescopes as unreliable, so I don't know what
> actually contributed to the star trailing. To those people - I would like to
> see what you call a failure.

See http://www.isomedia.com/homes/cvedeler/M45t.jpg. I don't call this a
failure as I am pretty pleased with this shot. However if I exposed much
longer the oblong stars would have been worse. I could not get away with an
11x14 enlargement of this shot due to the oblong stars. My standards have
increased to where this amount of trailing is unacceptable, and I hope to
reshoot M45 as soon as I finish building my observatory.

>
>
> I believe I have a workable system using my guidescope setup, but I do not
> have any long exposures to prove it. The only variable that I don't have
> complete control over is the primary mirror moving within it's cell, though
> I suspect that different examples of the LX200, particularly the larger 10"
> and 12" models, exhibit considerable variation in the movement of the main
> mirror. I do know that I have virtually zero image-shift when focussing at
> high powers, but this is a separate (though related) issue, I think, from
> the mirror 'flop' due to an insecure mirror. I do think that if your own
> scope exhibits significant image-shift when focussing then there is a
> mechanical problem with your scope that needs to be rectified before
> attempting prolonged exposures using a guidescope.

<snip>Ric, that shot displays very impressive guiding for 2 hours using a
guidescope! What type of scanner and at what resolution did you have this
scanned? If you are able to get results like this consistently using a
guidescope you are doing a lot better than I could ever do. On one occasion
during my tests to troubleshoot my guidescope / scope setup I went 90 minutes
with essentially perfect guiding. The problem was that I could never do that
consistently. I gave up on using my guidescope because getting only 20 - 30 %
of my shots well guided (to the kind of standards I talked about above) it was
just wasting my valuable dark sky time.


> > ----------
> > Sent: 28 January 1999 05:18
> > Subject: [M]: (M) Guider
> >
> > For anyone interest of a astrophoto of deep sky using a guide scope.
> > This shot was near the American Nebula on hypered Tech Pan film for
> > nearly 2 hours. The image is greatly enlarged to show detail. E-mail me
> > with the supplied link of your thoughts using a guide scope instead of a
> > Off-axis Guider.
> >
> > ric
> >
> > Photo at:
> >
> > http://members.aol.com/ceckers1/page/index.htm
> >
> >

Chris Vedelerhttp://www.isomedia.com/homes/cvedeler/space.htm
Tucson, AZ

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