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RE: RE: Low-Profile Focusser Problem

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Posted by Dennis Palmini on July 21, 2000 19:12:58 UTC

My thanks to Pete and Bob for responding. Sorry I haven`t replied earlier, but I`m teaching a 4-week summer course and have been busy.

The scope is nicely collimated, as far as I can tell. I checked it out last night and again this morning using a sight tube and Cheshire tube. Everything seems to be nicely centered and lined up. Before installing the focusser, the images were OK - sort of - but I suspect a small problem with collimation then. I knew nothing about the subject or collimation process back then.

I do recall one evening last summer being able to just barely separate the Epsilon Lyrae double-double, but the images, as I recall, were a little bit smushy and diffuse at high power; I was using 250X I think, a 9.7 mm EP with a 2X barlow.

Pete - I appreciate the comoment about the difference in focusser heights. I measured a heightof 8 1/2 cm. for the original Meade focusser vs. 4 1/2 cm. for the lo-profile focusser. So I should have moved the focusser and 2ndy mirror 4 cm. forward. Instead, I had space to move them a little less that one inch forward, about 1.7 cm. short.

When looking thru either eyepiece, I could not get decent images until I installed a one-inch extender. Even then, the high-power EP - 125X - gives images that are not as sharp as those at low power.

So a couple specific questions:
1) I know that images at higher-power will show less contrast. But are they also typically more smushy, diffuse, less sharp, than at low power?
[By the way, we don`t have an astronomy club or group in this neck of the woods. So I don`t have somebody local to ask these questions.]

2) I saw discussions of shorty Barlows in an earlier set of postings. Someone said they were designed to work better with low-profile focussers. Why? How?

3) Would I get better images at high power if I used a longer extender - say an additional one-inch extender, or a 2-inch one? [Yes, I know it kind of defeats the point of a "low-profile` focusser!]

Again, many thanks for your thoughts.

Dennis Palmini

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