Not reaching focal point?
Posted 11 December 2012 - 09:51 PM
Posted 11 December 2012 - 10:05 PM
Posted 11 December 2012 - 10:27 PM
Posted 11 December 2012 - 11:26 PM
Posted 12 December 2012 - 03:58 PM
If you can't reach inward focus, you either have to move your primary closer in (tightening the collimating screws as much as you can while still maintaining collimation will get you some without major tube modifications) or moving the focuser down closer to the primary. You also then need to move the secondary down to match.
Posted 12 December 2012 - 06:35 PM
Posted 12 December 2012 - 06:54 PM
Posted 12 December 2012 - 08:35 PM
1) You could use a lower-profile focuser (shorter).
So what if I move the mirror up as much as I can and nothing changes? What could be the next step? And it is a shorty Barlow.
2) You could use a TeleVue PowerMate instead of a standard Barlow (doesn't require the inward focuser travel)
3) you could remount the primary mirror higher in the tube (might necessitate changing the trunnions on the side of the tube since the balance point would change)
4) You could bring the secondary mirror a little closer to the focuser (say, by 1/4"), which would still allow you to collimate. It would tip the optical axis slightly toward the focuser, but that would only be of any importance if the scope had a set of digital setting circles (computer) attached to it, as it would reduce the accuracy of pointing.
5) You could try another eyepiece with a focal plane farther down in the eyepiece barrel. That would require additional out-travel of the focuser, which would be OK in your case.
6) You could use the barlow lens threaded onto the bottom of the eyepiece instead of in its barrel (if the barlow lens unscrews from the barrel of the Barlow). That lowers the magnification factor of the Barlow, but also requires less in-travel on the focuser.
7) You could take the focuser to a local machine shop to see if they could machine the focuser drawtube to allow more inward travel of the tube. If for example the eyepiece setscrew his the body of the focuser and limits the in-travel of the focuser, a slot in the focuser body could be machined to allow the focuser drawtube to move in even further.
8) You could use a combination of all of the above and achieve probably another 1/2" of in-travel. But I think either #5, #6, or #2 is simplest.
Posted 17 December 2012 - 07:07 PM
Posted 03 February 2013 - 12:25 PM
Posted 03 February 2013 - 02:22 PM
This one has 2 small steel setscrews to tighten on the eyepiece barrel.
Ok, apparently I did not solve the problem entirely. What about a negative profile eyepiece adapter? I haven't seen any reviews on it and I don't see on the picture of it how it would clamp or hold the eyepiece in. Anybody got any info on this product?
You could tighten them *just* enough to require a slight pressure to insert the eyepiece. That's typically how they are used if not a semi-permanent addition to an eyepiece.
That's a little easier with the similar adapter from Astrosystems.biz, (his website is incommunicado right this minute) which, IIRC, has a nylon setscrew to press against the eyepiece.
Either one will drop the eyepiece quite a bit IF the eyepiece is small enough to fit into the recess. Ironically, some larger eyepieces are, while some smaller eyepieces aren't. Trial and error prevails, I guess.
Posted 03 February 2013 - 02:24 PM
It "clamps" onto the eyepiece (or barlow) with two allen setscrews. In practice, I rarly use the setsrews, I just drop the eyepiece in....in most observing positions, gravity holds it in just fine.
IMO it's a good product, and Scopestuff is a GREAT supplier!
Posted 03 February 2013 - 07:01 PM
Posted 03 February 2013 - 07:12 PM
If you adjust the setscrews to touch the 1.25" barrel with *just* enough force to require you twist the eyepiece in or press it slightly, the fit will be tight enough. Maybe not tight enough to hold a heavy eyepiece upside down, but enough pressure to hold the eyepiece in.
So how does the eyepiece stay in the adapter without sliding out? Or is this something I would have to get for every eyepiece? I'm very interested in this product!! It might just solve my problem!!
Posted 03 February 2013 - 07:44 PM