Telescope Reviews: Re: Bobs Knobs

I think that perhaps the others HAVE mis-understood.

When you tighten one screw completly, lossening the other screws will NOT help you. Once a screw is bottomed, loosening the other screws will simply cause the secondary to become loose.

There are two circumstances that can cause this..

The first is internal damage due to over-tightening the secondary. It is VERY hard to damage the steel housing for the secondary, but it can be done.

There is little protrusion on the back of the secondary mirror mounting plate (a thick disk of steel) that sits on the bottom of an inverted steel cup (the baffle assembly).
When you tighten the screws, the little protrusion rocks at this point like a fulcrum on a see-saw.

If you get too overzealous in tightening these screws, it can deform the cup that the secondary holder. The little projection puts a dimple in the cup meaning that the pivot is lowered. YOu can run out of travel before reaching your collimation point.

The other condition that can cause this is that the corrector is not centered. This is most likely. Because the secondary is a -5 mirror, if it is not pretty perfectly centered over the central baffle, to "OVERCORRECT" this, you wind up cranking one screw down further than you normally would to get enough tilt to the secondary.. If it is bad enough, you simply run out of adjustment screw.

My guess is that you have a secondary centering problem. You MIGHT have a situaion where the cup is damaged, but this is unlikely.. It would be very hard to tighten the collimation screws this tight using the small Phillips head screws that came in the scope...

But it is entirely possible and even likely that over the years, the corrector has moved.

Using as accurate a ruler as you have, measure the distance out radially from the edge of the corretor to the retaining ring at several different places around the diameter of the tube.

If you find that the secondarly cell is not dead center, this is most likely your problem...

Regards.

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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)

The night sky is my mistress. She seduces me away from all other lovers.

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