Cheap parfocalising rings

Share practical advice and tips on making your own kit

Cheap parfocalising rings

Postby reggie » Wed Jun 11, 2008 8:00 pm

Hi all, in the quest for making my life easier I had a look at parfocalising rings, so simple in design I thought I should be able to make a couple. I used some of the tubing I bought from wickes that I used as the focus draw tube/EP holder for my homemade finderscope, it's got an inner diameter of slightly over 1.25" so its a very nice fit :) I simply cut myself off 2 pieces each 5mm in length (well, close enough :D) then I fished out some matching screws from my bits box with flat tips to minimise any scratching on the EP nosepiece, made a couple of appropriate sized holes 180deg from each other using a heated watchmakers screwdriver to carefully push through the side of the ring, screwed then in place and now I have a pair of parfocalising rings. I could've used 3 screws per ring but I could only find 4 matching screws so settled for 2 per ring, I don't think it really matters that much as long as you have a flat edge and can lock the ring in place.

Not something you would necessarily go out and buy the tubing for as it was ~£10 I think, but as i already had it for other purposes its cost me no extra outlay for these acessories and the saving on making 4 of these will have more than paid for the tubing and still gives me loads more to play with for other little projects, like some kind of attachment for my webcam to my 25mm plossl.
reggie
 
Posts: 485
Joined: Mon Feb 13, 2012 6:45 pm

RE: Cheap parfocalising rings

Postby sftonkin » Wed Jun 11, 2008 10:46 pm

I used to cut split rings from 35mm film cans (the OD is 1.25").
sftonkin
 
Posts: 2826
Joined: Mon Feb 13, 2012 6:22 pm

RE: Cheap parfocalising rings

Postby reggie » Thu Jun 12, 2008 12:26 am

Someone else suggested that to me as well, I haven't tried it but it seems another good way to achieve the same results. anything that makes the ep nosepiece bigger at the crucial point than the hole its being put into will do I'm sure. I'd also thought about putting masking tape around instead, although I didn't fancy the gunk if I ever needed to take the tape off.
reggie
 
Posts: 485
Joined: Mon Feb 13, 2012 6:45 pm

RE: Cheap parfocalising rings

Postby brianb » Thu Jun 12, 2008 1:00 am

[quote]I'd also thought about putting masking tape around instead, although I didn't fancy the gunk if I ever needed to take the tape off. [/quote]
The "gunk" from masking tape is hardly a problem to remove. However it may not be very effective as it will "give" slightly resulting in inaccurate setting of the focus ... and parfocalization is hardly worthwhile if imperfect.
brianb
 
Posts: 5513
Joined: Mon Feb 13, 2012 6:49 pm


Return to Telescope Making

Who is online

Users browsing this forum: No registered users and 0 guests