I bought a second-hand Canon 100D after I got into photography this summer, and got to use a vintage lens that was still attached to my dad's Pentax ME Super (Asahi Pentax-M 50mm 1.4 SMC, a great step up from the Canon kit lens that came with the camera).

Now recently I got a decent deal on some vintage K mount lenses, €30 for a Asahi Pentax-M 135mm 3.5 SMC in pristine condition, some Pentax 28-80 3.5-4.5 zoom/macro lens with stuck diaphragm blades, and a Makinon Zoom 35-105 f3.5-4.5 MC. The latter is the lens in question...

I couldn't get the lens to focus, and it had signs of tampering (some half-stripped screw heads, and the metal was scratched at the back from not using a proper lens opening tool) but nonetheless, it felt smooth, has no scratches on any of the glass, and just seems to work fine. So I examined it and all seemed fine. The only thing that I can find is that clearly the rear lens element/group has been opened (slight fingerprints on the inside of the assembly), so I dissasembled and thoroughly cleaned everything but still no focus.

So my theory is that whoever disassembled this first didn't leave all the lens pieces in the correct order and thus it won't focus.

I've done my research but can't find any diagrams of this lens so I can't verify it either. So to anyone with more experience on the matter, does my theory sound right? Or what else could be at fault?

And does anybody have a way of doing or order of operations to go about finding the correct order of the assembly? Because there are 8 total glass lenses, about 5 spacer rings and a inner tube piece to center the smaller lenses, so that makes for a heck of a lot of combinations of order.enter image description here

  • 1
    \$\begingroup\$ Was the focus just a little bit off or impossible to focus at all? Any other symptoms besides focus? Vignetting? Weird field curvature? Weird bokeh? Etc. \$\endgroup\$
    – xiota
    Dec 5, 2019 at 9:04
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    \$\begingroup\$ low-value lens, zoom, undocumented, and previously tampered with? That is not lens repair, that is masochism :) \$\endgroup\$ Dec 5, 2019 at 10:45
  • \$\begingroup\$ Its way out of focus if i point it at the black tv in front of a white wall from a distance of about 5 meters, there is only blur, turning it into macro mode seems to bring the focus closer so i can semi-distinguish the shape of the tv and weirdly enough pulling and adjusting the zoom allows me to get a bit better focus, but not 100%, turning the focus ring has a noticeable effect but very small, yet both the threads on the focusing ring and macro setting ring barely allow any adjustment without it either bottoming out or un-screwing completely... \$\endgroup\$
    – Nook
    Dec 5, 2019 at 12:55
  • \$\begingroup\$ @rackandboneman i know haha, but the pristine 135mm lens was already worth the 30€, and i dont know about the glass yet, but this makinon seems to have pretty decent build quality, smooth as butter.... aaand i quite like the challange \$\endgroup\$
    – Nook
    Dec 5, 2019 at 12:57
  • \$\begingroup\$ That's a lot of elements. It would help to know the shape of the elements. (convex, concave, plano, glued, etc) I'd try to put it back how it was and look for an element that was simply put in backwards. \$\endgroup\$
    – xiota
    Dec 6, 2019 at 3:02

1 Answer 1

  • Note whether there are any symptoms that indicate the elements may be out of order, flipped, or misaligned. There are other reasons lenses may not focus as expected that aren't related to elements being misplaced.

    • Focus may need to be calibrated.
    • The lens may be soft wide open.
  • Draw the lens diagram, as you have it. This can serve as a reference if you want to put the lens back to how it was. You may also be able to spot elements in positions that just "look wrong".

  • Try to find an official lens diagram. Diagrams of similar lenses may be helpful. Or you may find another copy of the lens to inspect.

  • Trial and error.

    • Lens groups tend to follow patterns. Some sequences are highly unlikely. The following pages should be helpful:

    • The first and last element in a group can often be determined by size. The largest element is usually in the front of the group. The smallest element is may be in the middle or rear of the group.

    • The spacers that are adjacent to elements can also be determined by size.

    • Elements are usually convex away from the center of the lens or group. However, there are notable cases where elements are flat or concave away from the center.

    • Glued elements are usually toward the front or center of the group.

    • Whether elements will hit each other can help determine their order and which way they face.

    • The above constraints should limit the number of sequences to try.

  • \$\begingroup\$ Starting from well known patterns is likely far less helpful with zooms as opposed to classic primes... \$\endgroup\$ Dec 5, 2019 at 10:51
  • \$\begingroup\$ @rackandboneman That's why I write "tend to follow patterns". There are exceptions, even in primes. For zooms, the individual groups of older zooms follow similar patterns. Newer zooms are more complicated, and easy to ruin by disrupting the electronics. \$\endgroup\$
    – xiota
    Dec 5, 2019 at 14:12

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