Lens dissassembly, assembly, optical benches, et al.
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?
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.
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.
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.
Originally Posted by clayne
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.
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?
Anyone can make a Digital print, but only a photographer can make a photograph.
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
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Originally Posted by David Lyga
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.
I photograph things to see what things look like photographed.
- Garry Winogrand
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. Thereís no adjustment possible, except for indexing the actual focus relative to the position of the focusing ring on helicoid-focusing lenses.
Itís 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 itís not.
Reverse it and the lens wonít 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.
The focusing ring now turns smoothly with the resistance Iíd expect of a new manual focus lens.
For AF lenses or manual focus lenses intended for arctic conditions Iíd use this.
Me too... and some of them have gone back together again!
Originally Posted by David Lyga
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.
For new-manufacture lenses the 'adjustment' involves either re-branding or a trip to the trash can if performance falls outside the established specs
Originally Posted by clayne
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.