collimating a TV Pronto?

Hello all,

Is collimating a TeleVue Pronto yourself advisable or is this best left to the folks at TeleVue? I'm an avid do-it-yourselfer so I'd like to give it a shot if it's feasible. However, I do not see three collimating push-pull screws on this lens cell.

With the lens cap on and using the cheshire I can see that the sets of small circles are not concentric. One set of circles is offset from the others by about 30-40% the diameter of the circle. In other words, they overlap but are clearly misaligned. I'm not sure how out-of-whack this is in the big scheme of things since I've never attempted to collimate a refractor, but a star at high power shows some asymmetry slightly out of focus, and doesn't snap into focus at any one point. There's a small range of equally mediocre focus positions. I also feel there might be an overall loss in contrast from what I remember this scope capable of when it was younger. Does this all strongly suggest that it's likely out of collimation?

Thanks for your advice,
Dan

I would leave it to TeleVue. The front lens cell is
attached to the white (or green) tube using three
black bolts on the cell near the joint. They usually
fill the bolt heads with black epoxy to prevent people
from messing with it. Collimation is achieved by
loosening the three bolts, tilting the lens cell,
and re-tighening the bolts. It will be hard to adjust
without an optical bench and some special fixture to hold
the lens cell while you make small adjustments.

The results you describe could be a variety of issues
-- poor seeing, thermal issues, bad diagonal mirror
or prism, etc. The offset you describe with the Cheshire
sounds like a very small error to me.

<>

I have always thought there is no real point in a telescope light path where the image suddenly is in focus. The out of focus condition gradually disappears as the light rays come together at the focal plane and then gradually disperse as they go beyond.

I think some folks see the snap into focus as their eyes quickly adjust to the image as it is focused with the end result that it appears to be a snap. But that is a combination of the telescope being focused and their eyes responding. The eye will adjust and see sharp images either side of the ideal focus, some folks do this better than others. Some like me, never see sharp focus.

I could be wrong. I'd like to hear more knowledgable people commment.

dan