Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Photograph by Tom Leonard
The Minolta MC Rokkor X 40-80mm F2.8 zoom is a unique lens, which uses a gearbox for controlling focus and zoom. The advantage of this design? It’s pretty small for an F2.8 zoom, especially one made in the 70’s, and more precise than a conventional helicoid. The downside? It’s fiendishly hard to take apart – as Roger Cicala and Aaron Closz at Lensrentals recently found out…
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
Roger and his team started by removing parts of the rear lens assembly, including the aperture ring. So far, so conventional. In Roger’s words: “We were starting to feel a little confident now. That confidence, as you will see, was entirely misplaced.”
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
Removing the leatherette that covers the lens barrel revealed several screws which – once unscrewed – allowed the gearbox housing to be removed, revealing the complicated mechanism for controlling zoom and focus.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
Inside the housing, you can see the macro selection and focusing mechanisms, both of which move what Roger is calling ‘The Magic Slot’ (indicated with a red arrow). If this looks complicated, that’s because it is. In Roger’s words, “this is a mechanical art of the highest order”, ensuring that even when the lens is zoomed, the focus point remains unchanged. That was impressive stuff for the 1970’s (and even today).
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
Back to the lens barrel, and things are getting even more complicated…
Here, the green arrow is pointing to the zoom stem, while the red arrow indicates a heavy duty brass post covered with a white bumper. Since “normal lens terms like helicoid and cam don’t work here” Roger is calling this ‘The Golden Post’.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
For a full explanation of exactly how all of this works, we’d recommend heading over to Roger’s original blog post, which explains things in fascinating detail. In the meantime, here’s a picture of the mechanical zoom and focus assembly, removed from the lens barrel.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
With this assembly removed, the 40-80mm starts to look rather more like a conventional lens. To completely disassemble it, though, the team referred to ‘Aaron’s Second Rule of Disassembly’. Specifically – All leatherette must be removed. Because underneath leatherette, you’ll invariably find screws.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
Finally, after “about an hour of time and a thorough and complete use of our full lexicon of unprintable words”, Roger and Aaron managed to get the inner barrel out of the outer casing.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
With the front optics taken out, the aperture blades were revealed. After such a complex disassembly, Roger and Aaron “were glad to see something that looked familiar”.
Lensrentals tears down famed Minolta 40-80mm F2.8 Gearbox Zoom
Image courtesy of Lensrentals
And here is the 40-80mm F2.8, reduced (almost) to its component parts. Roger’s final takeaway, from one of the most complex disassemblies he’s ever done?
“There were some slick engineers working on things at Minolta back in the 1970s, thinking way outside the box”.
If this article whetted your appetite, we’d encourage you to head to Lensrentals for a full explanation of the entire process (including MTF charts!) and read more about the unique 40-80mm F2.8 in Tom Leonard’s article, ‘A forgotten solution: Why this strange 1975 zoom lens is so sharp’. See links below.
Read the full article on Lensrentals.com
Read Tom Leonard’s writeup of the Minolta MC Rokkor-X 40-80mm F2.8
Articles: Digital Photography Review (dpreview.com)
