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Bausch And Lomb telescope cassegrain Criterion 4000 Astro optical tube 1984 USA For Sale

Bausch And Lomb telescope cassegrain Criterion 4000 Astro optical tube 1984 USA
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Bausch And Lomb telescope cassegrain Criterion 4000 Astro optical tube 1984 USA:

This auction is for a1984 Bausch And Lomb (USA) Criterion 4000 Astro optical tube. This will come with the standard, original goodies as well as a bonus:
* 4-inch schmidt optical tube* (4) original steel socket cap screws for mounting ota to the fork drive base* (2) original steel socket cap screws for mounting finder scope bracket to ota* (1) original front dust cover* (1) original thread-on 1.25-inch 90 degree prism diagonal with set screw* (1) original dust plug for the diagonal* (1) underside aluminum #1/4-20 photographic pan adapter for mounting to tripod* (1) 1.25-inch Eyepiece Adapter like new in original box BONUS!
Now that Eyepiece Adapter (mpn 63-1013) is indeed a bonus as these are hard to find, and because it will allow you to use a different brand-made diagonal. The thread-on diagonals these scopes come with have the problem that they are ONLY going to attach to other Bausch And Lomb Criterion cassegrains...or a genuine Criterion Dynamax. They are very well made, but there are better ones out there to be had for sure.With the eyepiece adapter (a visual back adapter), you can utilize a MUCH higher-quality 1.25-inch diagonal (like a Tele-Vue or Baader, or Celestron/Vixen true mirror 90-degree)....You can even use those wonderful-made Meade, Orion, and Celestron Japan-made 45-degree prism diagonals so that your Criterion 4000 will show fully correct images for the makings of a perfect terrestrial/birding telescope!
Those somewhat unfamiliar with the Criterion 4000 should know that these telescopes, though optically the same in both cases, did come in (2) different models: the fork driven "Astro" and the unmounted "Spotter". There are (2) distinct features that visually separated the 4000 Astro tube from the 4000 Spotter tube.1) The Astro tube has a dedicated thread-on 1.25-inch 90-degree prism diagonal (#63-1054). In the Spotter models, the diagonal is a standard 1.25-inch diagonal that fits onto the scope via a set screw on the threaded eyepiece adapter, or visual back adapter (#63-1013).2) If coming with the original finder, the Astro tubes had a black matte 4x18 finder on a cast aluminum, single bracket arm with (3) set screws. On the Spotter tube, the finder was a fancier 4x18 milled aluminum rifle scope on a XY-axis platform that was aligned via (2) geared screws.
These "Criterions" were so named because Bausch And Lomb bought the rights to the original Criterion namesake (well, first it was Bushnell and then Bushnell was bought by B&L) and later marketed their take on them with carried-over tones of the genuine products. The original Criterion Dynamax schmidt-cassegrains were handsomely dressed in white to cream-white tubes with graphite gray OR lapis blue fork mounts (different colors per generation) with red-and-black anodized accents. These scopes came in 6-inch, 8-inch, and there was also the very rare 4-inch. They ran from about August 1971- November 1981. The Dynamax 4 and the RV6 were the very last products under the Criterion name before they disappeared for good by 1982.
The B&L Criterion line was the 4000 (4-inch), 6000 (6-inch), and 8000 (8-inch). And these ran VERY strong from late 1982 untilthe last few months of 1986 (the last year I knew the all-black Criterions to exist).
The quality control on these Bausch And Lomb Criterion telescopes was wild and primal and as such there can be quite a few examples with poor optics and some with very good to exceptional optics. Over my years of experience collecting them, the Astro models had a much higher chance of sporting the good optics as they were considerably more expensive, and in a few examples still, their poor optical performance was due to uncorrected bad collimation rather than actually having a poor figure on the primary mirror.
Model: Criterion 4000Aperture: 102mm (4-inches)Focal length: 1200mm (f/12)Optical configuration: schmidt-cassegrainPrimary mirror: concave pyrex with aluminized coatingSecondary mirror: convex float glass aluminized coatingCorrector plate: float glass fully coatedFocuser type: primary mirror focusingMaximum usable magnification: 140xLimiting magnitude in very rural skies: +11.9Eyepiece barrel size: 1.25-inchTube length w diagonal in place: 12.28-inchesMain tube diameter: 4.51-inchesFinder mount screw pattern: (2) bolts 1.02-inch spreadMount to fork arms bolt pattern: (4) bolts (2) on each side of the tube 0.99-inches apartPhotographic plate adapter: will mount to any #1/4-20 boltMaterials: milled aluminum, cast aluminum, steel, optical glass, leatherette wrapWeight: 2 pounds 11 ounces with threaded diagonal
So there are pluses and minuses with these "Criterions".
Positives: Super smooth focusers that never wear; the best in the industry era. Longer focal length means achieving higher power easier. Very durable, but not too heavy. A small equatorial mount will hold it firmly. Front dust covers are fantastic and mist/rain will not get passed it. Internal optics are easy to reach for safe, touchless dust removal. Very easy to de-fork and use as a travel scope on a medium camera tripod.
Negatives: Manufactured by a firm that had poor quality control. Bolt on parts, such as the visual back adapter and 35mm T-adapter are brand loyal specific. Finder scopes on the forked models are too small for sighting most stars. Finder scope is too long for just (3) set screws to hold it firmly at all times. Low power hard to achieve at f/12. Internal optics are easy to reach even for kids.
I love their focusers; always smooth. I have NEVER owned a Criterion 4000 ota with a sticky or wobbly focus knob. Meade and Celestron fall short of them, and they never require any care.
Unlike all other 4-inch schmidt telescopes by Celestron, Meade, and even JSO, with the Criterion 4000, you simply unscrew the top corrector assembly just like you would take a lid off a large, glass jar. This is a very good thing because you don't have to risk shattering the corrector due to slipping-up on your grip with the Allen wrench. OR in the oldest models, you may need a unique spanner wrench, leaving the inside of the telescope completely inaccessible. And in the worst case scenario; you go to loosen the Allen bolts (or worse, Phillips screws) holding the cell in place and strip the bolt. Now you are locked out!!So the ability to merely unthread the top corrector assembly is a joy when needing to blow a clean puff of air inside and remove those pesky dust particles.The bad thing, of course, is a child with a good grip or some other irresponsible individual can have just as easy an access to the internals. As long as you keep this telescope in good hands always, this will never be an issue.
And for the many fine joys a Criterion 4000 can bring to the observer, it can just as quickly eliminate. The original finder scopes these telescopes came with do indeed have very sharp optics. BUT at 15mm aperture, they are not practical for sighting anything not at least -1.0 magnitude. So the Moon, Jupiter, Mars, Venus, possibly Saturn, Sirius, Arcturus and all of M45; that will be about all you'll sight in the finder.The finder is just fine for daytime targeting as you don't need large aperture for that. HOWEVER, this is a non-correct finder, so images are upside down AND backwards. It is indeed a usable finder, but not very usable.A final hindrance of many (but not all) Criterions by Bausch And Lomb is the extreme talent they had for poor quality control of the mirrors. I have had outstanding Criterions. I have had ashamedly horrible Criterions. The good and bad ones hide alike as ALL Criterions came mechanically sound from the factory. It isn't until you looked at your first peep of the Moon you realized it was going to be a fun scope or a chore scope. And back in the early 1980s, B&L made sure you, the complaining customer, had a very difficult time getting your money refunded.
A very important fact that any non-experienced Bausch And Lomb Criterion owner should know: like the original Criterion schmidt cassegrains branded "Dynamax", these telescopes use BRAND-DEDICATED adapters. The visual back threaded diagonal included with this telescope is SPECIFIC to work ONLY on Criterion Dynamax or Bausch And Lomb Criterion telescopes. If you lose this diagonal unit, you have to find another one used as they are several decades long out of production. You cannot use one from Meade, Celestron, Orion, Parks, or Lumicon.
This particular telescope in auction is a very good example Criterion 4000, but it is not the best one I've ever had; that one resides permanently with me. Nothing miracle about it, nothing bad. It is a 4000 that works as it should as advertised. It will keep up with most Meade 2045Ds, but not an ETX-105EC. I have yet to use a Celestron Nexstar 4 maksutov that can out resolve it. And none of these scopes, including the Criterion 4000, will touch a Celestron C4.5 (hey, that's a newtonian!!).It is an excellent scope for the suburbs and city where you'll be wanting to look at the Moon, brighter planets, and the very brightest deep sky objects, like M42, M13, M34, M35, and others. It will see all that nicely; though I don't attempt to push any of my 4-inch cassegrains passed the 150x zone often primarily because my skies won't permit and it is on my Manfrotto tripod usually.
When on the fork mount Criterion included with these (or with hinged tube rings on a Towa-style EQ-2 equatorial mount), you can go higher in magnification as those mounts are extremely steady. It also helps that collimation is checked every so often as the Criterion's secondary unit will lose collimation if vibrated enough. This model here I had up to 126x on the Moon with a Meade Series 3000 4-element Plossl 9.5mm in very stable sky conditions. I feel it could have edged a tiny bit more power, but I was missing the critical 8mm ocular for this test. Usually though, I rarely went beyond 110x.
In all cases, this is a GREAT terrestrial observer! These are FUN telescopes to bring with you on a camping trip for birding and visiting your favorite, bright deep sky objects.
And remember, this is an Astro-model Criterion 4000 with all the original mounting bolts already mounted where they should be on the scope. Should you wish to want to mount this to a Criterion 4000 Astro fork mount, it will be a very swift and easy activity as you won't need to search around for missing parts to do so.
Packed with great care.
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