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Bausch & Lomb 4000 repair?

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#1 BigC

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Posted 22 October 2012 - 10:06 AM

Here is what I did for at least temporary repair of my 4000.

On my Criterion 4000 the corrector plate holder simply screw on the end of the main tube .Grasp firmly and unscrew.Simple. BUT the corrector glass is held in the holder by a threaede ring with two holes.Being the impatient type I used a heavy paper clip firmly grasped as close to the ring as possible with pliers and was able to unscrew it.Scratching the glass was of no concern since it was already shattered in shipping. Not knowing any source for replacement corrector plates I had a glass shop cut disk from clear window glass.

Still have to collimate the scope(s) Actually "fixed" two this way;I 've had very bad luck with this model scope being shipped to me.

Can anyone say if the original was optically flat of shaped ? And where one might get correct replacements REASONABLY ?

#2 jrcrilly

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Posted 22 October 2012 - 10:28 AM

Can anyone say if the original was optically flat of shaped ? And where one might get correct replacements REASONABLY ?


The manufacturer advertised it as an SCT and I think we must take them at their word (any correctorless alternative would have required mirrors that were very expensive to produce in those days). It's a Schmidt corrector and not to be found on the shelf anywhere.

#3 orion61

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Posted 22 October 2012 - 11:08 AM

if the corrector was shatteed, the optical tube is a total loss, if you have the fork mount you could strip everything,
sell the finder scope and holder, the casr is nicely made and works well for an ETX. can you post a picture?,
did you take insurance?

#4 rmollise

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Posted 22 October 2012 - 11:18 AM

I was going to say that I wouldn't have gone to the trouble, since without that corrector you have an uncorrected spherical mirror. But, OTOH, some of the Criterion correctors I've seen haven't been much better than flat glass, anyway... :lol:

Seriously, these correctors were lenses. The only source would be another Criterion scope.

#5 Geo.

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Posted 22 October 2012 - 12:46 PM

There may be a source for replacement correctors in China. May be worthwhile pursuing this for a 10" or so, I can't imagine that it would be for a $100 optical tube.

I have an email address you can follow up on if you want to pursue it. PM me as the posting rules won't permit me to make it public.

#6 BigC

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Posted 22 October 2012 - 01:20 PM

USPS did pay off on the insurance and sent a letter they might want to inspect or pick up the item;that was maybe a month ago and have heard nothing more.Took pictures that are too big to post here. I may? need to install a program on this computer to trim the pic size.

As for the glass ,someone stated that some 4000 used a special mirrored seconady lense that allowed simple flat glass window.

The lady at the glass shop cut the disk out of scrap.A small donation to her favorite charity was the cost.

I figured there was little to lose by trying this and I might learn something.

#7 jrcrilly

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Posted 22 October 2012 - 01:52 PM

As for the glass ,someone stated that some 4000 used a special mirrored seconady lense that allowed simple flat glass window.


It's the primary that would have to change. Even if the secondary is changed to a paraboloid or, as in the Meade ACF, all the way to a hyperboloid, the spherical primary still requires a corrector.

#8 tim53

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Posted 22 October 2012 - 04:40 PM

Does it actually say "Schmidt Cassegrain" or might it say "Mirror Lens".

The Meade spotter version of the 4" was often a Mirror Lens - like a Klevtsov - which used a corrector lens doublet as a secondary. If you have it apart, take a gander at the secondary. Is it first-surface aluminized? Or is the aluminization on the back? Because if it's really a mirror lens, then you could use an optical window. If it's an SCT, scavenge the parts you think you might want to keep, crush the rest, and get the cryin' over with. :grin:

-Tim.

#9 BigC

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Posted 23 October 2012 - 12:24 AM

It seems that after buying FOUR of these,I will actually have ONE in working order by combining parts. I can use the star diagonal from the last shipping victim to complete the first 4000.I also acquired seperately the porro prism ,and solar filter.

I wonder if there is even a small central? portion of the FOV in which focus will be correct? I was able to see and read a sign some 400 feet away that appeared normal.Maybe the 4000 with flat glass can serve as a bird scope.

The secondary appears to be first surface.

Being the packrat ,not going to crush the unused pieces;someone may need a primary mirror to replace theirs.

#10 orion61

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Posted 23 October 2012 - 05:20 PM

You can try Fred Pauli here.. http://www.astroptx....bcriterion.html
He bought out all the old Criterion/B&L parts when they closed down, I know he has a couple of old New Stock 6" scopes for sale and misc parts/accys.
he takes a few days to answer.

#11 Starhawk

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Posted 24 October 2012 - 12:12 AM

Given how inexpensive used SCTs are in general, why not just replace the scope?

-Rich

#12 BigC

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Posted 24 October 2012 - 12:29 AM

Given how inexpensive used SCTs are in general, why not just replace the scope?

-Rich

Because fixing things gives a sense of accomplishment.Like those in the ATM forum.

I have other scopes,both smaller and larger.

Inexpensive is relative.

#13 Starhawk

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Posted 24 October 2012 - 06:36 PM

In this case, there is no real fixing unless you're prepared to make a custom SCT corrector. You could retrofit the optics from a celestron into the OTA, though I don't know what purpose this would serve. Sort of like building a Gremlin on a Pinto chassis.

-Rich

#14 orion61

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Posted 24 October 2012 - 08:36 PM

In this case, there is no real fixing unless you're prepared to make a custom SCT corrector. You could retrofit the optics from a celestron into the OTA, though I don't know what purpose this would serve. Sort of like building a Gremlin on a Pinto chassis.

-Rich

:funny:

#15 rmollise

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Posted 25 October 2012 - 06:38 AM

In this case, there is no real fixing unless you're prepared to make a custom SCT corrector. You could retrofit the optics from a celestron into the OTA, though I don't know what purpose this would serve. Sort of like building a Gremlin on a Pinto chassis.

-Rich


Well, maybe a Meade. Celestron hasn't made a 4-inch SCT...

#16 Starhawk

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Posted 25 October 2012 - 02:45 PM

Indeed. Just the one option for a 4". But then again, it's back to wrecking a perfectly good scope to make another.

-Rich

#17 BigC

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Posted 25 October 2012 - 09:58 PM

The Gremlin and Pinto filled a need for affordable small cars.I get tired of the negativity.

Back to the 4000. As the corrector plate on unit 1 is unbroken,the star diagonal from unit 4 will be moved there.Unit 2 had only a porro prism and unit 3 never arrived!Units 2 and 4 now sport window glass ,which at least protects the primary mirrors.

Attempted to view the Moon as test of just how bad a plain plate would be only to have clouds cover the whole sky,so will try another day,...err , night.


After looking at the damage to unit 4,and its case, and considering the foam lining plus the packing,I conjecture the scope was broken by the seller's shipping clerk. Point against the clerk is that he claimed to have wrapped the 4000 case in bubble wrap as well as packing the box with foam peanuts. There was no bubble wrap.

THe corrector obviously received a strong impact because the glass was not just cracked but the secondary broken out of the center and bits of glass speckled the main mirror.

Most likely the worker had a bit of difficulty putting the tube cover on, and SLAPPED it as I have seen many people do when putting a lid on a can or tube.Might not have heard it break.

Stuff happens.

Since my money was refunded,essentially I received a perfectly usuable diagonal , two eyepieces ,and some 1984- era telescope literature, and a spare motor ,all "free".

Certainly am not going to sacrifice a good scope to repair unit 2 or 4 to original specs.

#18 tim53

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Posted 26 October 2012 - 02:34 PM

I agree. I had a 1971 Gremlin X. It had poor weight distribution, but it was a sharp looking car!

Tim

#19 Dennis_S253

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Posted 26 October 2012 - 04:34 PM

I've always wondered about the corrector plate also. I was wondering how to check mine. I always wondered if it was put on backward. I love my 4" B&L. But, they did use a lot of wierd parts. The diaginal also appears to have a built in field stop. I do not believe any parts for a SCT will work on the B&L.

#20 BigC

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Posted 26 October 2012 - 08:12 PM

The B&L has a different thread than the standard SCT.At least it does accept standard 1.25" EPs!

Went back out in early a.m. and Orion was there so grabbed scope and patio table and looked up and Orion hidden by clouds again....pointed 4000 WITH WINDOW GLASS at Moon and waited for hole in clouds.Had a very strange view: focusing was very critical , and I saw ONE sharp image of the Moon with a couple blurred ghost images flickering in and out of sight.Note no collimation has been done yet.

The 4000 with a actual corrector plate wasn't tried as it began to rain.

The curve of the corrector must be very subtle but is there;I suppose one could measure the unbroken plate.I do not have the optical tools to do so.

Wonder how many of these scope might be stored away across the country needing a new corrector? B7L must have sold a large numnber as they advertised for a year or two on the cover pages of S&T and probably elsewhere.

#21 GolfSierra

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Posted 26 October 2012 - 11:19 PM

There was an B&L adapter available that allowed using standard SCT accessories on any B&L SCT rear thread. I had one for a B&L 6000 in the late 1980's. Any standard Celestron or Meade SCT thread on accessory could be used. The adapter part number would be found in the owners manual accessories list.

#22 BigC

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Posted 27 October 2012 - 10:38 AM

The problem seem to be such parts,actually any parts, are rare and priced as such. The fellow referenced earlier has few pieces listed online.There is a part or two I may buy after being satisfied the "survivor 4000" is usable.

#23 orion61

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Posted 27 October 2012 - 11:53 AM

I agree. I had a 1971 Gremlin X. It had poor weight distribution, but it was a sharp looking car!

Tim

I had a Pacer that was the most dependable car I ever owned,
cept summer with all those windows, could have made Jerky
in there..LOL
I'd part the 4000 out, I could use the "Silver" dec setting circles

#24 BigC

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Posted 03 December 2012 - 02:34 AM

An update for anyone interested.
Finally tried the 4000 with unbroken corrwector using the diagonal from another and verified thusly that the corrector is indeed shaped despite appearing flat to the eye.The view through the good one is fine,at least at 40x and 67x but the "repaired" front assembly with plain glass disc resulted in an image that was sharp only in the very center and distorted more the further from center as if looking through water.The plain glass was,of course , with a center hole and the secondary fastened in place as original.It just didn't work.

Wonder what the curve of the corretor actually is ?

#25 RichA

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Posted 26 February 2013 - 01:11 AM

If you want to experiment.
Look for a 4" Maksutov corrector, you are far more likely to find one of them floating around than an SCT 4" corrector. Convert the scope into a Maksutov, it would probably be better. Likely you'd have to extend the tube. Just don't pay too much for the corrector as the scope would have no real value itself.






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