The Minolta 40-80mm f/2.8 Gearbox Zoom; The Clockwork Lens

Published September 26, 2017

There were giants in the earth in those days . . . They were mighty men, men of renown.  Genesis 6:4

I’ve always been fascinated by the history of lenses. I write about it a lot. To me, the most fascinating items are those made many years ago, with what we would consider wholly inadequate technology, which did things we can hardly reproduce today.

Not long ago, I learned of a lens I’d somehow missed, the Minolta MC Rokkor X 40-80mm f/2.8 zoom(1, 2, 3).  Let’s pay a little respect to the innovation of this lens. It’s an f2.8 zoom, but has an only 55mm front element diameter, is about 10cm (4 inches) long, and weighs 560 grams (just over a pound) despite being all-metal construction. From many reports and examples, it has excellent image quality.

It is also completely unique (as far as I know) in being the only zoom lens driven by an external gearbox. There have been a few telescoping zooms. The first zoom, the Voigtlander Zoomar, used a sliding ring set on thick rods. Almost all other zooms have used a rotating helicoid to move the zoom groups.

But only the Minolta put a mechanical box on the side of the lens to drive the focusing and zoom elements., 2016

Moving the lever with your thumb to zoom the lens, spinning the wheel with your fingers focuses it, and moving the metal thumbscrew at the bottom in and out, puts the lens in macro mode., 2017

So when I got my hands on a copy of this unique lens, I had two questions. First, was it as good as they say it was? Second, how the hell does that gearbox thing work? Luckily, we had the capabilities to answer both questions.

Optical Testing

We didn’t have exactly the right lens mount for this lens but were able to make something work. At 40mm, though, the very edges of the test circle were cut off, but still, at 40mm and f/2.8 this is a pretty impressive performance for a 40-year-old zoom lens.

Olaf Optical Testing, 2017


At 80mm things were less impressive. This is a 40-year old lens, and things could have happened to it that affected performance, but further tests showed no decentering or field tilt. Still, it’s possible there’s a spacing error at the long end of the zoom range.

Olaf Optical Testing, 2017


When we stopped down to f/5.6 at 80mm, though, we were pretty impressed again. (This makes me think it unlikely that there is any real optical maladjustment here, it cleans up too nicely at f/5.6 to have a major optical issue.)

Olaf Optical Testing, 2017


My summary is it looks just like a good film zoom from the 70s would be expected to look. It’s pretty good at the wide end, needs to be stopped down at the longer end, but overall is a very usable lens. To get that in such a small package with macro capabilities, well, that’s impressive.

Of Course, We’re Going to Take it Apart

Be patient, though. We’ve never seen a lens even slightly like this, so we have absolutely no idea what we’re doing today. Most days we have at least a vague idea.

We had two hints, though. First, the lens is covered in a nice leatherette, like a camera body of the times. Leatherette is usually there to cover screws. Second, we could see some set screws around the barrel. You don’t see set screws in lenses today very often, but when you do, well, they need to come out.

So We Started with the Obvious

We removed the 3 set screws around the rear barrel., 2017

We were kind of impressed with these 1970’s set screws. As my friends from Boston would say, ‘they’re wicked sharp.’, 2017

With the set screws out, a rear ring, we’ll call it a makeup ring, came off., 2017


With that out of the way, we could see some real screws underneath., 2017


Taking them out seemed a logical next step., 2017

After removing those, Aaron could slide off the aperture control ring. We were starting to feel a little confident now. That confidence, as you will see, was entirely misplaced., 2017


The aperture control assembly is pretty routine. There’s a relatively long slotted key that inserts into the aperture ring. You can see a spring underneath it and a counter spring on the other side., 2017, 2017

You may have noticed the thick, brass spacing shim under the aperture ring. It’s in a location where it could be an adjustment for infinity focus, but we aren’t certain given its thickness. It might just be a standard, non-variable spacer., 2017


Then We Came to a Fork in the Disassembly Road

With the aperture control assembly off, there was a rear group sticking out that looked like it could be removed., 2017


There was also a rear metal plate that looked like it was made of tarnished copper. There were a couple of screws in the plate that looked as though they wanted to be removed. You may also notice the three black plugs in the plate. We weren’t sure what they were, but assuming the moving elements slid along some type of rail, we thought that could be the rail ends., 2017

While we decided which way to go next, we played around with the gearbox a bit, because with the rear of the lens barrel off you can get a nice, clear look at what the silver thumbscrew lever does. Turning it and pushing it in moves the lens’ optical assembly forward, basically like putting a built-in extension tube on the lens., 2017, 2017

This was done by Minolta in 1975. It was done again in 2013 when Canon released the 24-70mm f/4 IS Macro. (Mock me if you must, but the 24-70 f/4 IS is the lens I use most.) Minolta, in the 1970s and 80s, was arguably the most innovative camera company, with Nikon and Canon often playing catch-up.

Anyway, after playing around with the Macro button and turning the focus knob and zoom lever some more, we decided ‘neither of the above’ was the best option and started taking out the screws from the mechanical box cover. This is different for us because unlike today’s lenses, the screws were slotted, not JIS. We had to hunt around for a bit to find the right screwdriver., 2017

Removing the screws loosened the box, but it wasn’t going anywhere because the zoom lever and focusing wheel were still fixed in place.  The bit of leatherette on top of the focusing wheel seemed unlikely to just be decorative., 2017

So we peeled it off., 2017


And sure enough, there were some nice big screws under there., 2017

The focus lever lifted right off once those were removed., 2017


After that, we could lift the mechanical housing off. Notice that the center post, which controls zoom, is still part of the lens. The focus ring and macro thumbscrew mechanisms are part of the housing we took off., 2017


Well, How Do I Work This?

If you don’t like fascinating mechanics, you can skip this part. But we will all think less of you if you do.

Let’s start with the case we just removed, which contains the macro and focusing mechanisms, both of which move what, for lack of a better term; I will call the Magic Slot (red arrow) in the top case. As an aside, I would very much like to buy whoever designed this a beer. This, my friends, is a mechanical art of the highest order., 2016

I’m going to compress the images a bit to show you how things work. First, when we move the lens from standard (thumbscrew out) to the macro (thumbscrew in) position, we move the top side (in the picture) of the lever forward., 2017

If we rotate the focusing wheel, we move the lower side of the lever forward or backward. Closest focus is the image on the left below, infinity focus on the right., 2017


If you think that’s a little confusing, maybe showing you what the Magic Slot does to the lens will help. Or maybe not.

The green arrow points to the zoom stem, coming out of the field toward you. The red arrow is pointing to a heavy duty brass post covered with a white bumper, which I will call the Golden Post (because normal lens terms like helicoid and cams don’t work here). The brass base of the golden post slides up and down (in the picture’s orientation, it would be side-to-side on the lens) the two aluminum rods. And the rods are connected to the large aluminum base plate you see below everything else., 2017


The Golden Post inserts into the Magic Slot we showed you above. As we just pointed out, the Magic Slot moves forward and backward when you turn the focusing ring. This moves the Magic Post and therefore the aluminum baseplate, which is attached to the lens’ optical system forward and backward too, focusing the lens.

The copper plate with the curved slots rotates when you turn the zoom lever. (Helicoid plate sounds ridiculous, and I try not to use ‘thingie’ in these posts, so I’m going with a copper plate.)

You can see the two cam screws at the close ends of the slot in the pictures above and below. These move the zoom elements when the copper plate rotates. Aaron’s forceps are pointing to one of the cams in the picture below, shown with the lens zoomed about halfway. We honestly had assumed there was some type of worm-gear driving the zoom mechanism, but this is very similar to the slots you would see in the rotating barrel of a normal lens., 2017

In this position, you can also see a post with a black bumper that is sticking up from the copper zoom plate inserting into the base of the Golden Post.  There’s a closeup in the image below., 2017

The position of the zoom slides the brass focusing post from one side to the other along the rails. The focusing post is sliding inside of the Magic Slot, the position of which has been adjusted by the focusing ring and the macro thumbscrew. So the post is not only sliding from side-to-side, but it is also moving forward and backward depending upon the position of the magic slot., 2017

So things work this way:

  1. The focusing ring (and the macro thumbscrew) move the Magic Slot towards the front or back of the lens. Since the Golden Post is in the Magic slot, the entire lens assembly moves along with it, focusing the lens.
  2. When the zoom plate rotates, it moves the two zoom elements further and closer from each other, zooming the lens.
  3. When the zoom plate rotates, it also slides the Golden Post along the Magic Slot, readjusting its focus position.

This is an intense little mechanical computer. Changing the focal length automatically changes the focus to an appropriate location. Some modern lenses do something similar, where a series of keys inside the lens move the focusing group when the lens is zoomed. Others do it with electronic programming in the lookup tables.

But this is simple and elegant. OK, maybe it’s just elegant. I’m pretty confident a lot of engineers burnt up a lot of slide rules figuring all this out, but once the calculations were made, the mechanics make all the corrections automatically and should keep the lens fairly parfocal when zooming.

As an Afterthought, Let’s Take Apart the Lens

Obviously, I was most interested in how the zoom and focus mechanisms worked in this lens, but as long as we’re here, we might as well take the damned thing apart. I could say we wanted to clean and lubricate it, but you’d all know that’s a bald-faced lie. There were screws not removed and that makes us a bit crazy.

Anyway, by rotating the zoom plate, Aaron could access the screws that hold the mechanical assembly to the lens., 2017

And remove it., 2017


With that off, we can see how the zoom groups move. If you scroll back up to one of the pictures of the copper plate, you can see the two cams in their slots in the plate. With the pate removed you can see how each of those elements moves when the plate rotates., 2017, 2017


Now I could next show you a dozen pictures as we tried to, in order, remove the front ring, remove the copper ring from the back, remove the zooming cams. Well, we tried all of those things, but the lens didn’t disassemble. It rattled some but didn’t come apart., 2017


So next we went with Aaron’s Second Rule of Disassembly: All leatherette must be removed., 2017

This gave us access to nice, thick bolts that held most of the fixed elements in place. We removed these, of course, which wasn’t, perhaps, the best idea. (Actually it was our best idea, on the basis that it was our only idea. It just wasn’t a good idea.) When the first bolt came out, we heard the rather sickening sound of a nut of some type falling into the lens. This, my friends, was the point of no return. Now we had to get the lens disassembled, even if that meant using a circular saw.

Acting like we were cool with all this, because people were walking through the repair space, we took out the rest of the bolts, after which we were able to slide the front group part-way out of the lens. It was nice to see, even at 40 years old, there was a nice felt ring protecting the insides of the lens from the outsides of the world., 2017


It would have been nicer to see the optical group just slide right out. But, of course, like everything else about this lens, things weren’t as we expected. Our last vague hope was that, with the front group partially out of the lens, some more set screws were exposed., 2017

And after removing those, we could unscrew the front element from the rest of the front group., 2017

And, as you may have noticed in the picture above, this created enough of an opening to let us drop the ‘nuts’ out of the lens. All 8 of them., 2017


With the front group removed, we could see the remaining elements slide up and down on three relatively thick rods (you can see the ends in the image below, and the rods themselves in the next picture)., 2017, 2017

But the rods run inside the inner barrel. To get the outer barrel off, we still had to remove the focusing cams from their elements. We eventually accomplished this, using multiple applications of glue remover, heat, and torque., 2017


Finally, with those removed, we could slide the inner barrel out of the outer casing. These last few pictures represent about an hour of time and a thorough and complete use of our full lexicon of unprintable words., 2017, 2017


This gave enough access so that Aaron could get a grip on the second element and unscrew it., 2017

There were several spacing shims underneath that second group, which is the only true optical adjustment we found in this lens., 2017

Now, with all of the front optics removed, we have an unobstructed view of the aperture blades. They looked just like aperture blades, and at this point, we were glad to see something that looked familiar., 2017

We went to the back of the lens and removed the screws from the copper plate (well, copper looking, I don’t think it’s copper) at the back because those were the only screws left.  Of course, it would not come off over the rear element., 2017

Pulling it back did expose the rear end of the rods passing through the lens though, so we removed the set screws holding the rods in place., 2017

Then finally found more set screws at the front of the optical barrel, under the felt., 2017

With all the set screws removed we could push the rods up from the back., 2017

And suddenly we were done! With the rods moved up, the rear group slid right out. In retrospect, we could have done this a lot earlier and saved, well, time, sanity, and curse words., 2017

There was, of course, one more set screw to remove., 2017


After removing that, the aperture assembly unscrewed from the rear group., 2017


And only then could we take the rear group out from the copper plate., 2017

There was no reason to separate the rear group, so suddenly our disassembly was complete. (OK, you’re right. There was no reason to separate any of this stuff, except that’s what we do.), 2017

So What Did We Learn Today?

That there were some slick engineers working on things at Minolta back in the 1970s, thinking way outside the box. This was an entirely different way of making a zoom.

I have no idea why this didn’t catch on. It was smaller and in many ways simpler than competing lenses. It was, perhaps, too different. Or maybe just too difficult to assemble and disassemble (although I’m certain there were easier ways to do it than our fumbling about). It might have been more expensive to make. Or maybe it was too costly to keep making one clockwork lens when the others all used routine zooming and focusing methods.

But it’s an impressive example of some engineering gone wild, and I always love seeing designs that are outside of the box.


Roger Cicala and Aaron Closz

September, 2017


Addendum: Because many people were worried we wouldn’t be able to get this classic lens back together again:

Author: Roger Cicala

I’m Roger and I am the founder of Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Equipment
  • Christian Bosk

    I just followed your fantastic precise repair manual for the Minolta Zoom-Rokkor 40-80/2,8. I got one totally dismantled from a repair guy, he was unable to repair and reassemble it again. Now my 40-80/2,8 works again perfectly ! Thank you for this great article and all those pretty good Fotos!

    Have a nice time, with many regards,
    Christian (from Southern Germany).

  • Vulture

    You never had the radical idea of looking up a Minolta service manual for that lens BEFORE disassemble the lens?

  • Brett Rogers

    Well? Still waiting, Wheeler. You commented elsewhere three days ago. So you’ve been in Disqus.

    We all get things wrong occasionally. Difference is that some of us are prepared to acknowledge and correct errors. I believe it comes under the heading of “integrity”.

  • Brett Rogers

    Oh the TTL claim is just ridiculous, too. Zeiss Ikon, Topcon and ALPA, just for starters, were all doing TTL metering by the mid 1960s. High speed flash sync? Hate to break it to you but Compur and other leaf shutter makes were achieving 1/500 sync by at least the early 1950s. In my own collection here I have a Fujica 35-EE 35mm rangefinder circa 1961 with 1/1000 shutter that will sync electronic at its maximum speed—I have tested it. It’s likely it’s not a true 1/1000, nevertheless, just a tad faster than 1/250.

    No doubt you were thinking of focal plane shutter sync speeds—but not surprisingly, you DID NOT MENTION THAT.

    I think you owe it to the readers of your comment to cite reliable references for the remainder of your list of “firsts”, several having been so easily demolished.
    Over to you.

  • Brett Rogers

    “I could go on, but my fingers are starting to hurt!”

    I’m glad you didn’t. You’re running fast and loose with your claims. Are you just making this stuff up as you go along?

    The F was absolutely *not* the first camera to use a motor drive. Quite apart from the matter of any number of gun cameras used in WW2 aircraft, there’s the inconvenient topic of the KW Praktina 35mm SLR which debuted several years prior to Nikon’s F. This had both spring powered and electric powered motor drives available. It’s not as well known a camera as some other East German types, but is still quite well documented online and in print—look it up.

    As for the F being the first SLR in space—that is a preposterous claim. I can’t recall offhand which camera types the Soviets flew prior to 1971 but I believe these included some SLRs. It’s a moot point, anyway. The US flew Hasselblads during the Mercury and Gemini program. As for open space: that would be Gemini IV when Ed White used a Zeiss Ikon Contarex (Special) fitted to his gas manoeuvring system. No excuses for overlooking that one—his crew mate McDivitt took some photos of White with it through the open hatch. With a Hasselblad!

    I wonder how many of the other “firsts” in your list are also incorrect?

  • Michael Clark

    Last major camera manufacturer to FINALLY let go of the mechanically coupled aperture control and all of the disadvantages when compared to an all-electronic connection pioneered by someone else way back in 1987: well, you know who it is.

  • Mark Groep

    Great post Roger.

    I have now serviced my own copy having seen that it is not as difficult as I had been led to believe! It may be worth me adding a few hints to aid others if they read this blog.

    The front optics (and rest of the lens) are much easier to access if you first remove the front ring with the engraved lens designation. It is held in place by a single set-screw and it unscrews clockwise (i.e. it is a left-hand thread). No thread-lock used as far as I could see. Mine was really tight but screwing in the dedicated 62mm lens hood really hard loosened the ring it. I assume a 62mm filter rim or step-up ring would work equally well, but gives less grip. Using this instead of a filter vice is helpful as it actually forces the ring to expand a little, helping to free it. Alternatively it may work to screw in a 62mm step-up ring, and put a filter vice on that to unscrew both step up ring and lens ring clockwise.

    When removing the front optics, take note of its exact position. This lens cell is not screwed in all the way in, but is adjusted in the factory (presumably this is the fine adjustment for infinity focus). The shims you show under the second (middle) lens cell I assume to be the adjustment for par-focality).

    The rear lens cell simply unscrews as is, no need to loosen the set-screw you show. I assume yours was simply really tight, but mine had fortunately been assembled in-factory with a minute amount of damping grease in the thread to ensure the threads wouldn’t gall. Judging from your photos they didn’t do that on your copy. The copper-colored back cover can then also be removed by tilting it and then lifting out (it has been manufactured slightly oval, not round, and by tilting can thus clear the rim of the main lens barrel).

    As to why this zoom was constructed the way it is? I have to assume it has to do with the focus mechanism. The focussing and compensation cells seem to have been combined in this design, which means that the focus needs to be adjusted as the lens is zoomed. However, as focussing in this lens is unusual for a zoom in that all lens cells move in unison when focussing, perhaps the Minolta engineers deemed this mechanism to be the most practical. Who knows…

    I think a clue as to why this never caught on can be found in the component count of this zoom vs a conventional one! This must have been relatively expensive to both machine and assemble.

  • Arun Hegde

    Roger’s comment made me think of something Sir Edmund Hilary said when asked about the possibility of Mallory and Irvine, both of whom died during the attempt, having summitted Everest decades before him and Tenzing Norgay:

    “I’m rather inclined to think, personally, that maybe it’s quite important, the getting down.”

    I am similarly inclined to think that maybe it’s quite important, the reassemby part!

  • Mike

    I just mentioned it on a different page here, but Minolta made optics for some Leica R lenses, and apparently complete zoom lenses , as well, per (1992) Laney’s Leica Collectors Guide.

  • Ralph Hightower

    This has been the most fascinating lens tear-down and I’m glad that y’all were able to reassemble the lens. It’s amazing what camera and lens designers could do with 1970’s technology. I wonder what Canon FD lenses could be like if they were designed using the resources available today. Although I have a Canon 5D III, I continue to shoot film with my 30 year old Canon A-1 and used Canon New F-1.

  • Ralph Hightower

    I didn’t buy the HP-35. I bought the HP-45 when HP introduced it. I also had a slide rule for use in engineering and chemistry classes. I loaned my slide rule to a coworker in the 80’s who wanted to learn how to use one; he moved and I never saw it again.
    I still have the HP-45, but it no longer works because the battery is dead and the power supply also. I’m a big fan of HP calculators and RPN. I also own the HP-67, two HP-41. The HP-16 C and HP-48S, 32S II still work.

  • Andrea Aprà

    I found the original US patent of this lens. It was the US3930720 filed: 18 Feb 1975.
    The inventor/designer was Kyozo Uesugi of Minolta Camera Kabushiki Kaisha (that mean Minolta Camera Co., Ltd.)

  • Chris Keats

    yes. and in a fair, or unfair fight. the xe-7 will crush any opponent. I mean physically crush them. In 2000 (and maybe one) we were at the montreal gp, after qualifying we were having some afternoon sharpeners when an errant waiter went by and caught the strap of my xe-7 (with 200 2.8 attached). off the table and onto to the tiled floor it went. it broke a tile. camera was fine. still have it.

  • Max Manzan

    Very interesting indeed. Thank you for sharing.

  • Cranky Observer

    Many other camera makers also licensed technology from Minolta in the 1970s and 80s, often via confidential deals that weren’t revealed until many years later.

    I’ve thought, what would have happened if Kodak had used the money they threw away on the APS-C film system to buy Minolta and start true digital integration from a strong camera and customer base… But it was almost impossible for foreigners to buy Japanese companies then.

  • Max Rockbin

    It’s nice to think that maybe Minolta’s heritage is being carried on by Sony. It’s been just over 10 years since Sony bought them and came out with their first Alpha. A little history/tribute to the purchase here:

  • You really don’t want to know what Aaron’s time costs.

  • DrJon

    You need a rental page for Aaron’s time – how many people here have pulled a camera or lens apart and failed to put it back together… 🙂
    Oh and I have this Rollei TLR… well most of it… probably…

  • Anonymousse

    Is it for sale/rent? 🙂

  • Gene Mushak

    I had an x700 film – loved the little bugger and the metering / focus screen was great!

  • John Shriver

    You can do crazy aspheric surfaces in a plastic lens. Even the disposable 35mm cameras have aspheric lenses! Gives you a huge leg up in lens design.

  • Adam

    I’d heard this referred to as a clockwork lens before, honestly expected gears rather than cams. Cool design! Get the urge to break out a 3D printer and clockwork convert a broken kit lens? 🙂

  • Brandon Dube

    Going to space is not an innovation, it is merely being selected for a mission by NASA.

    High speed motor drive is evolution, not innovation, unless a novel technology is invented to enable that speed.

    f/2.8 is not “ultra fast.” In that time, large diameter high homogenaeity and low striae glass was not available from glass manufactures. You could make your own, or you could not produce large lenses. Leica and Nikon both have made some of their own glasses throughout history, as did Kodak and Polaroid. Probably others too. The choice to produce large glass is perhaps innovative, but aerospace companies e.g. Itek were making meter class optics at the time, which dwarf the puny front element of a 300mm f/2.8.

    A high speed shutter is, again, evolution.

    A 1700mm lens is not at all innovative. Manufacturing large elements aside, a 1700mm f/8 represents the easiest refractive camera lens ever designed.

    TTL, HSS, in-lens CPU, and VR are real innovations.

  • There are not 12 individually moving groups, I believe there are 12 elements. You could say they all move as basically the entire optical assembly moves to focus. Two zooming groups actually move on helicoids.

  • Already done. See the addendum 🙂

  • EVener

    That is one impressive piece of engineering. For your next trick, you’ll be reassembling it so that it is back to being a working lens, right?

  • Gareth

    One question, after reading the dpreview article afterwards – they describe the lens as being 12 groups each individually moving – but I don’t think the photos don’t show that.

    How many optical groups are there?

  • Najinsky

    LOL. I signed up to DISQUS to post the above. Shortly after the post I got a ‘Welcome’ email saying:

    “Discover some of the best discussions happening in the community from breaking news to Batman. There’s a discussion for just about any topic.”

    Ever get the feeling you are being watched?

  • Najinsky

    Thanks Aaron and Roger, most entertaining duo since Batman and Robin. It’s now official, you’re my favourite waste of time.

    Now, after that fascinating interlude, what the heck was I supposed to be doing….

Follow on Feedly