[AZ-Observing] Re: Bausch & Lomb
- From: gene lucas <geneluca@xxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 21 Nov 2005 15:34:28 -0700
Hi Stan,
AFTER you determine the correct orientation/adjustment (tilt AND
rotation) of the meniscus lens (by squaring it on, probably by
"autocollimation" with a Cheshire style eyepiece or one of the laser
alignment gadgets), I would recommend permanant shimming with some
harder but compliant material. Contrary to Thad's opinion, I would
favor a hard paper type material with only a little compliance or
"give". There are various hard paper-type gasket materials available
(automotive store), or you could just use aluminum foil strips, shim
stock, or plastic tape. Or maybe cork sheeting. Depends upon whether
or not you need to have the whole arrangement "waterproof" or rugged
enough to go hiking with it!
You might prefer to locate a large synthetic rubber O-ring, like the
original. (Look in stocks at a hardware, plumbing supplies, or pool
supply store.) Do you suppose the original O-ring might have been
coated with some sort of grease, making it soft and causing it to
deteriorate? If the OTA is just going to be mounted as a guidescope,
then obviously you don't need the lens to be mounted with an O-ring
gasket. I don't believe it is necessary to have a continuous sealing
ring all the way around the periphery of the lens, esp. if you keep the
lens covered against dust when not in use. Spacing (thus the thickness
of the shim or spacer) is not the issue -- the >distance< from the
meniscus to the mirror is not critical, but the proper tilt and
alignment is. So a thin, stiff material might be right for the replacement.
This is most likely a Cassegrain-Maksutov system. The whole trick here
is to get the lens squared on to the primary mirror, also checking that
everything is centered with the primary baffle tube. (Cassegrain
systems must be baffled properly.) Complicating matters, there is
likely no adjustment provided for the primary mirror tilt or centering.
Now you know why the B&L scopes are no longer made. B&L was already on
its way out of the optics business, when they bought out Criterion
Manufacturing. Criterion's "engineering" on their Maksutov and SCT
scopes was abominable. Whereas they did make pretty decent Newtonians.
Jack Johnston kept one of their SCT scopes in his shop as a sales aid to
show people why they should buy one of the other brands!
There is no possibility of getting any repair parts for the Criterion or
B&L telescopes, long out of production. B&L is completely out of optics
manufacturing now -- the famous old plants in Rochester, NY (my home
town) have been bulldozed. They market only opthalmic products and
contact lenses exclusively. They also bought out Bushnell Optics some
years back (marketers of good quality Japanese spotting scopes and
binoculars). The Bushnell and B&L trademarks still appear on some
binoculars and "outdoor optics" products, but the trademarks are owned
by a midwestern marketing company. Actual production is now from China.
Gene Lucas
(17250)
Thad Robosson wrote:
>>Questions: Could this easily be corrected by discarding the rubber seal
>>and cut out and put in a spacer made of thick automotive gasket
>>material? Is there another solution someone may be able to suggest?
>>Stan
>>
>>Stan, I'm not sure if I would use the gasket material. Being a paper
>>product, it might very well compress over time giving a sloppy fit. You
>>might see if you can find a suitable urethane product. Urethane is made in
>>several properties, one of which is very rubber-like. The benefit is that it
>>doesn't deteriorate like
>>rubber. As an example of it's longevity, urethane bushings are used in many
>>automotive situations. Conditions considerably more extreme than a telescope.
>>
>>Thad
>>
>>
>>
>>
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