Re: [APML]: Fw: Guidescope advice sought

[Steve Bell <sb635@delphi.com>]

Chuck Vaughn wrote:
> 
> 
> > I have been unsuccessful in attempting to use my Cookbook camera to offaxis
> > guide.  I am using a 16" f/4.5 Equatorial Newt and a Lumicon Newtonian
> > guider.  It is impossible for me to get the CCD in focus while offaxis,
> > while the film camera is in focus at prime focus.
> 
> Can you make an extender to put on the rear of the OAG to place the camera
> farther back? This in turn would push the off axis focus out farther.
> 
> Personally I would make a separate guidescope on a newtonian my last choice.
> Flexure is hard to beat on all but short exposures.
> 
> Chuck  <aa6g@aa6g.org.

I have very nearly the identical type scope, and that's exactly what I
had to do. First off, though, I replaced the high profile 2" Meade
focusser with a low profile 2" JMI focusser. That allows you to get the
OAG's pick-off prism closer to the tube, which then throws the focal
point out further through the off-axis tube. This helps in getting the
CCD camera in focus. Once you can get that, then start using extension
tubes to move the film camera out. When using the Lumicon unit, you have
to abandon using its supplied T-mount - the one that has the lip that
the three setscrews dovetail down on. You can slip 2" Lumicon extension
tubes into the 2" ID hole with the three setscrews, but then you need a
regular camera adapter with the correct T-mount. You have to play around
with extension tubes of various lengths, but you can usually find a
combo that allows concurrent main film camera/off-axis CCD camera focus.

-- 
Clear skies,
Steve Bell
email: sb635@delphi.com
Astrophoto page: http://people.delphi.com/sb635