focuser travel problem with Paracorr

Drats.

I bought a used 2" Paracorr with tunable top. Unfortunately, I couldn't get anywhere near close to focusing. Need a lot more in-focus distance toward the secondary, I'm guessing at least another 1/2 inch. Up until now I have had no problems focusing with a variety of eyepieces.

Anybody else with this experience using a Paracorr? Did I do something wrong in using it?

My current focuser is the JMI DX3, relatively inexpensive and single speed. Is there a better brand that would allow more travel?

I'll try moving the primary mirror up too with the collimation bolts, but I've got a long way to go.

Thanks,

Mike Ratcliff

Mike,
sorry to hear about the problem. I have been thinking of getting a Paracorr myself, I guess I had better check that out.
If the collimation bolts won't get you enough travel, then you will have to come up with a inventive fix.
With one truss I built a new focuser board and moved the secondary. This is the last thing you will want to do though.
Has the DX3 got a spacer under it? Do you have the drag screw loosened on the DX3, that will not let the barrel travel the last 1/4" if it is not loosened.
Floyd

Mike,
sorry to hear about the problem. I have been thinking of getting a Paracorr myself, I guess I had better check that out.
If the collimation bolts won't get you enough travel, then you will have to come up with a inventive fix.
With one truss I built a new focuser board and moved the secondary. This is the last thing you will want to do though.
Has the DX3 got a spacer under it? Do you have the drag screw loosened on the DX3, that will not let the barrel travel the last 1/4" if it is not loosened.
Floyd

I had this come up on a Starmaster that originally had the older-style Paracorr with the lower profile tunable top. The newer Paracorrs have a higher profile top. I raised my primary up and that solved it. I've also talked to people that just decided to rotate the tunable top down lower than is recommended by Televue for a particluar EP, which also solved the in-focus travel problem, but possibly reduced the effectiveness of the Paracorr farther out in the FOV.

Good luck,
Doug

The paracorr does require an extra 1/2" of in-travel compared to without the paracorr. If you are using 1.25" EP's, you can get a low profile 2"/1.25" adapter that will give you most of it. For 2" EP's, try raising the primary on it's collimation screws like Floyd suggested.

Jarad

About a month ago, I posted on a problem reaching focus with a used Paracorr just purchased on Astromart.

I shortened the truss tubes 1/2 inch, and still had weird problems. I figured something else must be going on.

Turns out the main problem was that I was given both a tuneable top and an older fixed top, and that I had stacked BOTH on each other without realizing what was going on. DOH!

This of course made the paracorr-eyepiece spacing way off, you're just supposed to use just one top. The tuneable top is newer and preferred.

The Paracorr makes a nice difference with the 16" f/4.9 and a 17mm Nagler T4. For me the coma was very noticeable before.

Thanks for all of the suggestions.

Mike

Any problems I've had with a paracorr have been self-induced: Focusing was no problem with any EP when I first set up my scope with the paracorr, but my tendency when collimating had been to turn the adjusting bolts counterclockwise, or out, which effective lengthened the distance from the primary to the EPs. Finally my 17mm Nagler wouldn't come to focus, until I systematically turned all three collimating bolts in to shorten the distance.