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
  • Fanboy much?

  • Brett A. Wheeler

    “Minolta, in the 1970s and 80s, was arguably the most innovative camera company, with Nikon and Canon often playing catch-up.”


    World’s first autofocus lens: Nikon 80 f/4.5 1971
    First SLR in space: Nikon F 1971
    First 5 fps motor drive: Nikon MD2 1972
    First LCD display: 1980 Nikon F3
    First exposure meter fully coupled with aperture: Nikon F 1959
    First motor drive camera: Nikon F 1959
    First ultra fast telephoto: 300 f/2.8, Nikon 1971
    First built in TTL (through the lens) exposure: Nikon F3 1980
    First 1/4000 shutter: Nikon FM 1982
    First camera with matrix metering (now the industry standard): Nikon FA 1983
    First high speed flash synchronization: Nikon FE2, 1/250, 1983
    First TTL-BL mode for balanced background exposure with flash: Nikon SB24 1988
    First CPU lens: NIKKOR 50mm f/1.8, 1986
    First camera with built-in red-eye reduction: Nikon TW20QD in 1989
    First underwater Auto-Focus SLR camera: NIKONOS RS 1992
    First vibration reduction technology: Nikon Zoom 700VR 1994
    First 1700 mm lens: Nikkor 1200-1700mm f/5.6-8P IF-ED 1990

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

    Yes, Minolta had some firsts, but in the 1970s and 1980s, Nikon OWNED the professional camera market. There is a reason that Nikon and Canon thrived, and Minolta was forced out of the camera business in 2006.

  • davev8

    that’s not good …if i disassemble something and leave it a week …which means invertible 3 weeks ..some gremlin comes along changers how a remember it coming apart and steals a small part

  • Reading, and rereading, Asimov is one of life’s pleasures. Thank you for the reminder!
    This was actually one of the longest projects we’ve done. Total of about 10 hours of my time and a similar amount from Aaron. He did the reassembly, I wrote the post.

  • Joshua Koerner

    It sounds like you all go through hell to do these things, from unprintable hours (by the way, that took me back to reading Asimov! Fun little word, unprintable!) to all the work to clean, lube, and reassemble. It sounds like you all have to make some dedicated time to get all this done, and that it takes more than its fair share of time to do them. Just wanted to say thank you for it nevertheless. You consistently have the most interesting articles to read, and while I know that may not be enough to keep doing it from a pain-involved-in-doing-it perspective, until you stop, they’ll be appreciated :). (And after too!)

  • Please!!

  • Athanasius Kirchner

    That post would be very welcome, especially if you could also talk a little about molded asphericals and the size limitations manufacturers face for them (I’d love to know what’s the current status).

  • Remember when you were a kid and one friend had all the bad ideas, but the other had the car you needed to get to where the bad ideas were? That’s me and Aaron. I have the bad ideas but I couldn’t do the tear-downs and reassemblies.

  • They’re starting to. The Sony FE 70-200 f/2.8 GM does and I think a couple of others.

  • Marty4650 .

    Roger… if there ever was any doubt that you are “King of All Lens Geeks” then this teardown should cement your position.

    All of us other geeks thank you for your meticulous work. Someone had to do it, and you and Aaron are clearly more qualified for the task than any of us are. This is why you will always be the King and always command our respect and appreciation!

    I really love the way designers and engineers can go “all out” to create something technically beautiful (when you let them) but impractical and difficult to repair. Someday, this sort of engineering will be a lost art. But at least in the meantime we still have Lensrentals to do this important work for us.

  • William Dyer

    I used to shoot Minolta cameras and lenses. I had the Minolta XK (non-motorized), and the Minolta XE-7, which Leica based one of their cameras on. Both were sturdy, metered well and were very reliable. Then came autofocus and obsoleted all my Minolta lenses. I switched to Nikon as they used a mount that would accept both autofocus and manual focus lenses. Still, those Minolta XK and XE-7 cameras were impressive gear.

  • Samuel H


  • We’re about halfway through clean, lube, and reassembly. Remember, leatherette is made to peel off, just like camera grips today, during any repair. The age may make it a little brittle, but we have new leatherette we can replace it with if necessary.

  • Samuel H

    I’m puzzled by the fact that fly-by-wire lenses don’t do all these adjustments automatically. It should be very simple.

    And linear EM focusing should allow for more groups to move independently of each other. I guess it takes time to change designs to allow these options, so we’ll see more and more of this in the coming years.

  • Marc P.

    Minolta Lens Engineers have been genius, that long time ago. So far, the lens was being introduced into my birthday year, so it must be great. :~) Thumbs up, Roger & Crew, for showing us these internals. As a sidenote, do you guys really got this lens reassembled & working again? I mean, the nice faux leatherette…huh. It’s mechanically a complex design, way complex for it’s heyday.

    I remember these days into the mid 80’s when i was a child, and the 1st Minolta AF SLRs came out….and even more, how much, many hours i was standing at the local photo gear shops, and have always being looking at these way nice Carl Zeiss C/Y lenses….i have known nothing at that time about photography, but these “weird marks” onto the Lens barrel for a child like me back between ca, 85-87 then have been way interesting, and i was really curious, how these Lenses are being operated onto the SLR, and i’ve had already known that the ZEISS brand is not only expensive, but must be really good into quality terms…one day, when i grew up…i’d own some of them…i thought to myself…i remember also quite the moment, when a gear shop owner let me look through the viewfinder of his Mamiya M645 camera….oh boy, that was such a huge & bright viewfinder….i’ve never seen before back then as teenie. 🙂

  • prescient

    “Acting like we were cool with all this, because people were walking through the repair space…”
    Heh, heh, heh 😉

  • Shane Castle

    “Minolta, in the 1970s and 80s, was arguably the most innovative camera company…” I have to agree. I still have a Maxxum 7000, my first AF camera. (One value estimate I got for the entire kit was $45 – 3 lenses, remote release, external battery pack, etc.) Sigh. The AF speed was godawful by today’s standards, and it often hunted with the long zoom (a 100-300mm) and in low light, but I used it up to the 2000s, when I finally purchased a DSLR.

  • Brandon Dube

    30% make it into a cell phone, not the trash 🙂 Yield doesn’t matter when it takes about a minute and 20 seconds to make a mold with 30 lenses on it and the material is relatively cheap plastic.

    As a US lens designer, I have limited visibility into the plastics used by the chinese molded optical manufactures, but if you want to google around the plastics I know by name are E48R, K26R, SP1516, EP5000, PMMA-O, Polystyrene-O, Polystrene-O, ZF52R, and OKP4. I’m sure there is e.g. EP6000 or EP7000, and they are just not materials I have access to.

    Maybe I’ll write a cell phone vs DSLR blog post…

  • Brandon Dube

    If you want some real amazement, Fuji is usually credited with introducing computers to optical design/optimization around 1973 or so. In the US, Hopkins had some papers on it in the 1950s or so, but from a research perspective using a supercomputer at cornell for some exorbitant fee paid by the institute of optics. His conclusion was basically that the computer would replace the rooms of young women lens designers were using as calculators, but never replace the thought of the designer in optimization. These days you basically hold the optimizer’s hand and push it around the solution space, how very wrong he was.

    In the mid 1960s, Kodak actually had built a mainframe computer based on 4 Friden electro-mechanical calculators that could trace about 1000 rays an hour. This machine appears in no publications and is otherwise secret, except for its appearance in a promotional video Kodak released at the time that John Grievenkamp showed in his talk “Optics Goes To The Movies” at IODC 2017. No one knew what the machine did, since it is not mentioned in the film, but Robert Shannon worked at Kodak at the times and remembers it as a raytrace computer. The Friden machines were several thousand dollars, and allegedly had a lifespan in this machine of about 4 months before the solenoids that pushed their buttons and read the results wore them out.

    I looked and can’t find the video online. I could email Dr. Grievenkamp for a digital copy…

  • Thank you, Amit. I included that one in the references, but it’s worth repeating.

  • Amit Kotwal

    Thanks for the teardown! This is a fascinating lens (The only one I ever saw had a broken front element). This article ( talks about the motivation behind the unusual design.

  • You are certainly correct, Chris. Which makes me sad. . . . I loved the mental picture of slipsticks and pocket protectors, heaping ashtrays on the tables. . . .

  • Chris Jankowski

    Fascinating article, Roger. Thank you.

    However, a nit picking correction might be in order. The HP-35 pocket scientific calculator appeared in 1972 and the whole engineering community (myself included, as a engineering student then) switched to it from slide rule nearly instantly notwithstanding the substantial purchase cost. It was like changing from a stone axe to a chain saw. And from 1968 the desktop hp 9100A scientific calculator was also available although its use was not widespread, as the price was prohibitive – equivalent to about $35,000 today.

    So, perhaps the Minolta engineers did not have to use slide use when designing the lens.

  • I bet Brandon will be around shortly to give a better answer. But the two things I know are small image sensor helps a lot, and the automation makes them so cheap that they test them at the end of the assembly line and don’t mind if 30% or so go in the trash bin. Plus the small size makes that testing very easy and automated.

  • Max Rockbin

    I LOVE your history articles! Just brilliant stuff you can’t really get elsewhere on the internet. Thank You!
    Request: I know it’s not in the lensrentals business line, but I’m sure many of us are curious about the optics of good phone cams. How can they possibly resolve so well with such apparently excellent contrast and light gathering when they’re so tiny, have so few elements and more often than not are made of plastic! (What kind of plastic? Eyeglass type plastic?). Why isn’t diffraction an major limiter? etc.

  • Deanaaargh

    Fascinating, Thanks.
    I think the inclusion of a video or even a GIF of the Magic Slot in action would be very helpful.

  • J L Williams

    This has been my favorite teardown so far! I had one of these lenses “back in the day” — it was about the only wideish-to-portraitish f/2.8 zoom that wasn’t crap — and I was always curious what was inside that box. Little did I know it contained a Magic Slot!

    People might not think it from reading the description, but the thing was convenient to shoot, too — with your left hand supporting the lens, the focusing wheel was right under (actually over) your thumb, and the zoom lever/swinger/thingie was right next to that. Very clever minds at Minolta back then…

  • Usually I say read the post in reverse. In this case, since we disassembled it in ways it was not meant to be disassembled, that doesn’t work. Assembly order involves putting the reassembled optical assembly back down over the rods. Truth is it isn’t done yet because the disassembly took waaayyyyy longer than expected and we ran out of time. We need to clean all the glass up, clean and lube all the mechanicals, etc. It will take a full day to reassemble and we won’t have a free day for another week.

  • Roger Cicala

    Usually I say read the post in reverse. In this case, since we disassembled it in ways it was not meant to be disassembled, that doesn’t work. Assembly order involves putting the reassembled optical assembly back down over the rods. Truth is it isn’t done yet because the disassembly took waaayyyyy longer than expected and we ran out of time. We need to clean all the glass up, clean and lube all the mechanicals, etc. It will take a full day to reassemble and we won’t have a free day for another week.

  • Clive Moss

    Wow. Next can you show us how you put it together again?

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