Telescope focuser as extension tube?

[Davids]

Has anyone tried adapting a crayford style telescope focuser as an extension tube? Something like this:
https://www.bhphotovideo.com/c/product/ ... g&c3nid=98

There are different styles of focusers and it looks like they might be adaptable for a tube lens/objective set up or reversed enlarger lenses. Borg also offers helical focusers that look promising. Not exactly cheap, but also not as exorbitant as a Schneider unifoc.

http://www.sciencecenter.net/hutech/borg/focuser.htm

I'm curious to hear opinions or experiences.

[rjlittlefield]

I do not recall seeing any report of using a Crayford style focuser.

Helical focusers with standard threads, such as Borg's 7841 & 7842 with M42P1.0 threads, are a common method of making focusable extensions.

I have one of the inexpensive chinese M42 helical focusers purchased through eBay and have had no difficulties with it. At this moment it is serving to support the camera on my microscope's trinoc port, as a way of making the camera be parfocal with the eyepieces.

--Rik

[Troels]

I would not use such one for focusing a macrolens or objective beceause the good ones are rather heavy and bulky.

I obtained a very nice one at a time when I thought I would upgrade my newton telecope from 1.25" to 2" focuser. It turned out to be too heavy for my dobsonian mount . And eventually I could not stand the cold winter nights in Denmark any more.

So my $200 crayford 2" focuser started a new life as a perfect and luxourious hight adjustment for my object table. With silk smooth 1:10 fine adjustment and locking screew. Any 2" tube fits nicely into the ocular holder so it is easy to custom build a rotating table from plumber fittings and a cheap microscope x/y adjustment table.



Troels

[SONYNUT]

works great on my c8.. haven't tried it with a macro lens though.