Lens dissassembly, assembly, optical benches, et al.

Discussion in 'Camera Building, Repairs & Modification' started by clayne, Mar 21, 2012.

  1. clayne

    clayne Member

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    Why do people insist that in order to re-assemble a modern multi-group lens that one has to have fancy equipment for realignment of elements when the lens itself has no such facility for even adjusting groups relative to each other?

    Take any typical prime lens and you'll notice the same construction paradigms in use:

    1. Common outer barrel that multiple groups, usually front and rear, slide into and are secured with threaded rings - almost always accessed by a lens spanner.
    2. Individual non-cemented elements being secured within a mechanical group via threaded rings and machined inner-barrels.
    3. Absolutely no facility for adjusting any of the elements relative to each other. No set-screws for offsetting element alignment, fore/aft, etc.

    About the only adjustment I can see is individual rotation of elements and how that might affect light relative to other elements. Other than that it seems as if the ultimate "alignment" of the lens as a whole is purely determined by the machining tolerances of the barrels each group fits into.

    What am I missing here?
     
  2. Steve Roberts

    Steve Roberts Member

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    My experience is only with Pentax lenses, but based on my experiences with those I agree with everything you say, i.e. there are no adjustments so what's the big issue?
    I've usually embarked on disassembly of lenses because of fungus growing within them (a problem which seems to affect Pentax lenses particularly badly - I have various lenses from Tokina, Vivitar, etc. and have never had that problem with those). Once I've taken apart a lens once (and made spanners for the threaded rings encountered) it's a simple matter to repeat the operation every couple of years as necessary. I do, however, restrict my efforts to lenses that I are relatively plentiful and cheap these days. For more unusual and expensive to replace lenses such as my SMC Pentax 24mm, I prefer to call on the services of Michael Spencer, as I did recently.

    Steve
     
  3. jordanstarr

    jordanstarr Member

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    You're not missing much, if anything at all. Every lens I've ever taken apart has been relatively simple. If it wasn't, it was because the lens itself was being difficult (ie. parts refusing to be unthreaded). I think a lot of it has to do with a cash grab -make it seem so overly complicated and daunting that you must seek professional help. It's the same thing with cars. Go to a mechanic and tell them you've never done an oil change before and they'll try to talk you out of it, say you need all these tools and all the things you could do to ruin your car, etc etc. and that you need to pay them to do it.

    Some people also just hear rhetoric like "NEVER TAKE APART A LEICA LENS!! THE PRECISION IS SO PRECISE AND THE SECOND IT COMES APART YOU'VE KNOCKED IT OUT OF WHACK!!!" and then just repeat it all over forums without having a clue what they're talking about. Well, I've taken apart nearly every lens I've ever owned and even some with built in shutters that weren't working and fixed them without a manual or anything. I've taken apart all my Leica lenses (28mm, 35mm, 50mm), some canon rangefinder ones for cleaning, etc. and they still take sharp and beautiful photographs. I even made to repairs to my Leica M6 without any instruction. It's mostly logical mechanics and yes, there are SOME things you shouldn't try...ever...unless you're trained and know what you're doing. But for the most part, you can dink around with a couple cheap cameras and learn the basics with just some precision screwdrivers, spanner wrench and some other simple tools most people have lying around the house.
     
  4. paul ron

    paul ron Member

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    You are correct in saying it isn't rocket science but beware of reversing some elements that seem to be similar on both sides, watch out for shims as they are the critical adjustments done at the factory. Some lenses have paper thin brass shims you may be over looking in the seats. Watchout you don't chip the edges of some elements in deep seats as you lift em out. When cleaning with alcohol, be careful not to wash off the edge blackening.

    Otherwise, go have fun. I always inspre people to take an adventure n learn someting new.. most of these lenses are more than abundaant n cheap as dirt. The worst that will happen to a broken or filty lens is it will still be broken or filthy when you are done.

    The hardest part, as mentioned above, stuborn screws n parts that strip n self destruct in the process of dissasembly.

    Did I mention the time traveler that snatches parts n never puts em back, messin with the time contineum, when it comes time to put it all back together, missing parts? That tiny ball bearing, a single screw, flipped elements out of order?

    .
     
  5. David Lyga

    David Lyga Subscriber

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    Countless lenses have been taken apart by me. And then put back together after everything was cleaned.

    TIP: when cleaning elements use water that has a drop of dish liquid in it so that static electricity will not attract the dust. Then clean both sides simultaneously with an extremely clean soft tissue by turning the element between the two sides of the tissue.

    What you REALLY have to beware of are the short lenses like 28mm or, worse, 24mm. These are VERY complex as to how the elements are put together and, just as important, which SIDE of the element is to be placed.

    Many times I completely remove the dried up grease on the helical (with lighter fluid) and re-grease with a tiny amount of Vaseline. You do not need the large amount of grease that almost all manufacturers used when building the lens. Only Nikon was sensible enough to put only a tiny amount of this lubricant on the helical. The others put too much and, as a result, these old lenses become difficult to focus unless the dried up gunk is removed. - David Lyga
     
  6. semi-ambivalent

    semi-ambivalent Subscriber

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    David,

    Vaseline? Are you being serious? I'm not condemning here; I have a 105mm Nikkor-P with a really stiff focusing helical, and if Vaseline works, doesn't creep or run when it's hot outside, I'll try it. I've had this apart before and, with no CRC groups to be found, the hardest part is getting the helicals back together in the right relationship and that's easy enough. If Vaseline has worked (and worked well) for you I'll give it a go. I'll order some of the "real stuff" too. :smile:

    s-a
     
  7. Ian C

    Ian C Member

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    With respect to the original question, your observations are the same that we all see upon disassembling a lens for service.

    The positioning of the parts is determined by the maker. There’s no adjustment possible, except for indexing the actual focus relative to the position of the focusing ring on helicoid-focusing lenses.

    It’s possible in some cases to incorrectly reverse the orientation of individual elements. If the element is asymmetrical, the optical quality of the lens is spoiled. This could easily happen with a double convex element with slightly different radii of curvature on each side. It might look symmetrical to a cursory examination, even though it’s not.

    Reverse it and the lens won’t function properly. Too, the metal surfaces on which the element seats against can damage the glass and coatings if reversed because the shape of lens and seat are not mirror image as intended.

    My first helicoid CLA was to a 50/2.8 Zeiss Tessar. I used lithium grease. The turning resistance was so great that I almost needed pipe wrench to turn it. Vaseline (petrolatum) is too dense for most focusing helicals. I then replaced the lithium grease with this.

    http://www.micro-tools.com/store/P-HG-30/Grease-Helical-30-Medium-8ml.aspx

    The focusing ring now turns smoothly with the resistance I’d expect of a new manual focus lens.

    For AF lenses or manual focus lenses intended for arctic conditions I’d use this.

    http://www.micro-tools.com/store/P-HG-10/Grease-Helical-10-Light-8ml.aspx
     
  8. benjiboy

    benjiboy Subscriber

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  9. Steve Smith

    Steve Smith Subscriber

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    Me too... and some of them have gone back together again!

    No manufacturer of a mass produced item would design it so that every part needed expertly applied precise adjustments. A good design is one where you can put all the pieces in a box, shake it and have a finished part fall out (an analogy a QA manager I used to work with would use). Not literally, but I'm sure you know what I mean.


    Steve.
     
  10. ic-racer

    ic-racer Member

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    For new-manufacture lenses the 'adjustment' involves either re-branding or a trip to the trash can if performance falls outside the established specs :smile:

    Re-cementing certain lenses, of course, does require some exacting method of alignment. Specifically those lenses where one element of a cemented doublet is not in contact with the lens body.
     
  11. steven_e007

    steven_e007 Member

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    Well... as someone who has worked in an optical factory and has watched technicians stripping down and reassembling optics, I can tell you this:

    There isn't a lot of adjustment in most modern lenses. The glass sits in seats in threaded modules and these screw into precise register.

    Not so much older lenses, where the glass can be moved around with lens spanners in the mount to get the centring correct. With these I never take the glass out of the brass (or aluminium) mount.

    So... most lenses should go back together in the same registration and alignment as they started with.

    But. Big BUT.

    After reassembling the optic it would then be carefully tested for alignment just to check it was within spec. Usually it was - but it is possible a foreign body got under the seat or a spec of something stopped a thread from fully returning to it's register. The other possibility is just making a mistake - leaving a spacer out or putting a shim in on the wrong side. Occasionally this would happen and mean that something might be a little out of adjustment. Often it would just mean dismantling, cleaning the thread or seat and re-assembling again.

    But without the optical bench and calibration equipment - how would you spot this? You have no quality control check for reassembly errors.

    If I'm going to strip down a lens I at least take some pictures of a test chart or something first - so after reassembly you can check the before and after and see whether you've trashed the performance.

    Although personally, my rule of thumb is to dismantle as little as you need to to do whatever you need to do... For most jobs the problem is usually replacing lube - which doesn't require too much dismantling of the optical parts of the lens - or removal of dust, which maybe just requires a front element taking off or something.
     
  12. clayne

    clayne Member

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    Are you specifically talking floating-element or CRC lenses? I'd think the same level of attention to detail would hold for any lens (strict order and up/down orientation being followed). Is there something specific you meant by "side" of the element? I'd think that one would never willy-nilly flip an element regardless of it being an 18mm or a 50mm lens but wanted to understand if you meant something else.
     
  13. Peter Simpson

    Peter Simpson Member

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    My experience with Vaseline (coating battery terminals on my car) is that it runs like the devil. Something you want when water/acid-proofing terminals and stranded wire, but something I would think you don't want when dealing with lenses. I would opt for some hi-tech silicone grease that stays where you put it. Shouldn't cost a fortune, if you look at an industrial supply company instead of some specialist optics supply place.
     
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  15. paul ron

    paul ron Member

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    Helical grease is not a lubricating grease.. it is dampening grease intended to give resistance... as you can see MicroTools is rated Medium n Light grades.

    Vasaline is not a good choice of lubricating medium as it gets watery n runs in heat as well as out gas over time, that in a lens is a bad mix.

    Before lifting an element, mark the top surface with a magic marker and use a small suction cup to get it up. Clean the marker off last before it goes back in so you don't make the mistake of flipping it wrong side up.

    .
     
  16. Newt_on_Swings

    Newt_on_Swings Member

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    I have worked on a few lenses/ shutters in various sizes. I never worrried too much as well either. Just simple unscrewing, cleaning, and rescrewing it back. I just worked on two a few days ago. But I never worked on any that were too complex. I have done small range finders, TLRs, primes, and zooms.

    Its not too hard, just organize and keep track of parts and use common sense and/or guides.
     
  17. clayne

    clayne Member

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    As a person who's rebuilt engines on my own and of course heard the common lines along "you'll shoot your eye out!" I can attest to this type of thing.

    Yep the Leicaphiles seem to be particularly paranoid about this - but they also believe there is an implicit magic in both the cameras and lenses (disclaimer: I do love my M4+Summicron). Speaking of which, I might have to crack open the Summicron as oil on the blades has migrated to the rear element and I'm not really into the whole diffusion effect. Any gotchas I should know about? As you can probably tell, there is zero documentation out there (only the chosen ones are allowed to fix these lenses).
     
  18. Grytpype

    Grytpype Member

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    Most Carl Zeiss, Jena lenses (pre. about mid '70s) and Meyer and Pentacon lenses DO have an offset adjustment for the rear element/s. This is best left alone unless you have to strip them to clean fungus, and if you do, you need to try very hard to re-assemble them exactly as you found them.
     
  19. Mark Crabtree

    Mark Crabtree Member

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    Which Summicron? I have to take my 8 element 35 apart every once in a while to clean out a very slight haze that builds up. It is straightforward, but there are a couple shims to make note of. I seem to recall that the 6 element 35 was very simple. The 50 DR is also straightforward as best I remember, I haven't had any reason to take my newer 50 apart so don't know much about that.
     
  20. clayne

    clayne Member

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    Hey Mark, it's a summicron 35 v4. The latest one before ASPH.

    Basically oil has seeped out past the blades and onto the inside of the rear group.
     
  21. Mark Crabtree

    Mark Crabtree Member

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    One warning - You could be getting into the time frame when the optical unit was glued into the focusing mount. I really don't know for sure on yours.

    On my earlier 35 Summicron there is a retainer in the rear that holds the optical unit into the focusing mount. Take off the retainer and pull out the unit. Then, I believe, the rear will just unscrew and get what you need. I think the 6 element version just before yours was the same.

    If yours isn't held together that way, you may still be able to unscrew the rear optical cell without disassembling the lens. Probably not much to get a grip on though (pieces of bicycle inner tube are handy grippers). If there is a single retainer slotted for a spanner in the rear, it will likely only get you the last element or cemented group, but sometimes is tight enough that the whole cell will unscrew.

    If you don't like the situation when you look it over, Sherry Krauter is very good for this. Edit - Oops, I see that would not be convenient from your location.

    If someone is more familiar with this particular lens, hopefully they'll speak up. I've only had that version in my possession for a couple weeks several years back.
     
  22. Leigh B

    Leigh B Member

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    Binning.

    All manufactured components have tolerances. Binning is used to minimize the impact of those tolerances on product quality.

    Speaking here of high-end photographic lenses, not the junk you buy from some mass retailers who could care less about quality.

    Any manufacturer of precision equipment uses binning to select which specific parts will work best with which other parts.

    One common measurement for a lens cell might be the distance from the mounting face to a principle plane.
    Depending on the quality of the particular lens, these might be graded as nominal, +0.1mm, -0.1mm, etc.

    Other major groups of the lens are similarly binned.
    So a front cell that's +0.1mm would be assembled with a barrel that's -0.1mm to achieve the correct overall dimensions.

    This is universal practice in precision assembly.

    The net result is that any particular sample of the product that you pick up would already have the selection made,
    so you could likely dis-assemble and re-assemble it without seriously disturbing its performance.

    Now, can you provide some published substantiation for your assertion that manufacturers lack proper measuring equipment?

    If not, you're just blowing smoke.

    - Leigh
     
    Last edited by a moderator: Mar 23, 2012
  23. clayne

    clayne Member

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    When did I say that manufacturers lacked measuring equipment? I don't remember saying that. All I meant is that with a single sample of a lens there typically won't be anything to adjust other than focus' reference to infinity.

    Basically there's no way for a user to adjust alignment of elements if the lens barrel assembly has zero facility for doing so. The only thing the user can do is follow strict disassembly/assembly protocol. I think that's a pretty sane assertion.

    The whole point of this thread is in breaking down the bullshit protectionist mysticism surrounding camera and lens maintenance.
     
  24. mtjade2007

    mtjade2007 Member

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    I once picked up a Rollie medium format projector from a flea market for $15. The reason it was so cheap was the zoom lens for the projector came in a bag of a dozen or so of glasses and an empty lens barrel. I figured in the worst case I would have to find a replacement lens for the projector.

    Well, I tried all possible combinations of orders and the sides of all the glass pieces to reassemble the lens. Some of the glasses due to the size were obvious. So there weren't too many possible combinations to try. Within one hour I found a combination that would project a sharp image on the screen. I then cleaned each piece of glass and reassemble again. I have had a perfect Rollie MF projector ever since.

    I guess to some people as soon as the lens is disassembled and the glasses mixed up it becomes a paper weight. Not really.
     
  25. benjiboy

    benjiboy Subscriber

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    People only post about their successes, not when they have made paperweights of them.
     
  26. Steve Smith

    Steve Smith Subscriber

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    Couldn't care less?


    Steve.