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How to dismantle Bell & Howell Super 8mm Projector Lens?


Jacek Kropinski

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Does anyone have a schematic or any information on how to dismantle a Bell & Howell 18-30mm projector lens? I recently came across a superb 462A projector that is like new in every respect except the lens has fungus on the inside elements. I can split the lens in two with the removal of two side screws in the picture, and have removed the back element but cannot get to the internal elements. Any suggestions or information would be greatly appreciated. 

 

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Primes are bad enough, but zooms... very tricky.

I see spanner slots in the rear of the lens;  you'll need a lens spanner and/or some friction tools at a minimum.

Forgive if you know all this stuff, but a good general tutorial site is Richard Haw's site for repairing lenses;  https://richardhaw.com/lens-camera-repair-fundamentals/  He covers still camera lenses, but the principals are the same.

Wish  I could be of more help!

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1 hour ago, Frank Wylie said:

Primes are bad enough, but zooms... very tricky.

I see spanner slots in the rear of the lens;  you'll need a lens spanner and/or some friction tools at a minimum.

Forgive if you know all this stuff, but a good general tutorial site is Richard Haw's site for repairing lenses;  https://richardhaw.com/lens-camera-repair-fundamentals/  He covers still camera lenses, but the principals are the same.

Wish  I could be of more help!

Thank you Frank. Yes, I have the back off and have separated the lens into 2 sections but can't split the main section to get to the inner lenses. I suspect some kind of adhesive is holding them together - I think it might be easier to get a new lens they go for nothing on eBay. But FYI lenses are not as scary as they look - I've cleaned many in my lifetime and it's generally a fairly simple mechanical process.

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Jacek,

I have to suspect that you are correct in that by the time your lens was manufactured, they were probably not designed to be serviced easily; just replaced.

Once you get a good replacement, you could perhaps then go at the old lens with a bit more "gusto" and maybe understand how it was assembled for future reference.  I sometimes do this just to satisfy my own curiosity if the lens is otherwise useless and headed for the landfill...

I hate to toss any lens, but sometimes it cannot be avoided.

I've cleaned quite a few primes myself; most aren't bad, but I have run into some assemblies now and then that are either over engineered or just worn-out and irreparable due to non-existent spare parts.

Good luck with your quest!

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8 hours ago, Jacek Kropinski said:

But FYI lenses are not as scary as they look - I've cleaned many in my lifetime and it's generally a fairly simple mechanical process.

Ha, that depends entirely on the lens in question!

For most of the lenses I work on as a cine lens tech I need a test projector and autocollimator to check and adjust them before and after re-assembly. It’s very easy to introduce decentration or tilt aberrations that may not be immediately apparent to a lens owner who may just feel that the lens isn’t quite as sharp as it used to be. 

Just one example: if you remove the front element of a Zeiss Ultra Prime, you will have lost the finely calibrated element centration and introduced off-axis flare and uneven field sharpness. It will still form an image, just a sub-par one. A technician will need to perfectly recentre the element while projecting it on a test projector. Many modern cine lenses have adjustments like this - sometimes in the front, sometimes the back, sometimes a floating group, sometimes even the rotational position of each element is critical - so be very careful attempting to clean inside lenses like this, even if it seems as simple as undoing a lock ring or removing a few screws. 

Obviously cheaper, mass produced stills lenses or older lenses tend to have fewer (if any) adjustments, and the elements usually go back together just fine within their pre-centred housings, but I’d still be careful with anything very fast or very wide.

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Some pictures of the front or inside the split sections might help determine if there’s a way in to your projection lens. Does the front section rotate? Is that the zoom part, that changes focal length, while focus is simply sliding the entire unit in and out of the projector housing? 

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On 10/21/2021 at 11:57 AM, Dom Jaeger said:

Some pictures of the front or inside the split sections might help determine if there’s a way in to your projection lens. Does the front section rotate? Is that the zoom part, that changes focal length, while focus is simply sliding the entire unit in and out of the projector housing? 

Yes Dom - I also have a Eumig and the design is the same but the Eumig (being German) has a superb design and come apart very easily.

Here is a photo of the section I cannot separate - it looks as if there is a join or seam where the zoom part enters the machined silver and black 'hood" but short of putting it into a vice and destroying it, I have tried everything to twist or pull it part. Knowing if it was pushed together or screwed together would help. There is no access from the front of the lens (that I can see) which is how the Eumig lens comes apart.

IMG_1472.jpg

Edited by Jacek Kropinski
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The front section: there may be a joint disguised as or hidden by one of these step rings within the hood but I have looked with a magnifying glass and can't see one on the outside. The shadow from the light makes it look as if there is a joint here at the top but there isn't that I can see. Having a schematic diagram or knowledge of the lens is I think the only way one could know where the join is.

IMG_1475.jpg

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Can I assume you have tried a friction tool on the inner, stepped ring on the front element?  Almost looks like there is a thread where the seam meets the outer, smooth ring...

Of course, it could be like some of the later Olympus 35mm still camera primes that have a glued-in beauty ring which you have to pry out (very scary). 

Edited by Frank Wylie
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1 hour ago, Frank Wylie said:

 I assume you have tried a friction tool on the inner, stepped ring on the front element?

Yes Frank I have tried everything on the front, the machined section, and the back section - that step on the front element is a shadow as I mentioned - i looked very closely with a jeweller's loupe and can see no seam in the front unless it is hidden.

There is definitely a seam on the back where the zoom tube meets the front machined head but not knowing if it is  pushed on or screwed in so I don't know which way to exert more force. It is a very cheap and mass produced lens so most likely it is glued rather than screwed but I don't want to destroy it unless I have to. Getting close to that though ?

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I would guess the two parts in your first photo are screwed together and sealed with a light glue. I would run some acetone in the seam and use a pair of rubber strap wrenches to undo them. Sometimes light heat can help, but be very careful of causing element delamination or separation, especially in cheap optics like this.

 

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40 minutes ago, Dom Jaeger said:

I would run some acetone in the seam and use a pair of rubber strap wrenches to undo them

Thanks Dom: I 'll try that. Read about the acetone in that great guide you posted above but wasn't sure where the seam was. The back element was screwed in very tightly and when I managed to remove it saw that a light shiny adhesive or lacquer of some kind had been applied to the thread there which made it difficult to remove. Wish I had known about the acetone then!

Really appreciate your expertise and knowledge thank you. Once I get it off I'll let you know.

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