RE: [APML] Can't Reach Prime Focus, What Are My Options?

["Thom Iwancio" <tiwancio@sc.rr.com>]

Dave,
	If you are really close you may just be able to move the primary
forward enough using the collimation screws.  This is particularly true
if it is a push-pull arrangement. 

If you have to cut the tube, aim for the middle to top of the focuser
travel so you won't have the racked in focusing tube protruding into the
light cone.  You can always add a tube extension to reach focus with
eyepieces.

All the best,

Thom Iwancio
Elgin, SC
www.machunter.org
home.sc.rr.com/thomiwancio


-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of Dave Mueller
Sent: Thursday, September 11, 2003 11:01 AM
To: Discussion of Film Astrophotography
Subject: [APML] Can't Reach Prime Focus, What Are My Options?

HI,

I have a Discovery 8" f/7 PDHQ reflector with a 2" JMI focuser, and I'm 
using a Nikon F3.  The JMI is 1.5" tall and won't allow the camera close

enough to the tube to reach focus (but it's really close).  I have the 
Baader 2" T ring adapter, it only adds 10mm.

So far, I've come up with the following:
1) Relay lens
2) New low profile focuser (like the Clement one, but at $400, it's half

what the scope cost!)
3) Build a simple flange to replace the focuser and slide the 2" adapter

up/down to focus
4) Re-do/replace the tube and move the secondary closer to the primary 
(and maybe need a new secondary?)

I realize a ready-made Newtonian isn't the best for prime focus work, 
but it was the most bang for the buck (and works great with my ToUCam 
and home made adapter).
Is there some other option, like a 1.4x lens type tele-extender that 
would provide a simple solution?

Thanks,
Dave

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