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The rear element of a Zenitar 16/2.8 Fisheye is shattered. What can I do to be able to continue using this lens?

shattered element

I know it is a clear filter. It cannot simply be removed because it is an essential component of this lens – hence it is the rear element. The lens is physically incapable of being adjusted to focus to infinity without a filter present. Note that the filter is represented in the optical design:

optical design
Image from All Photo Lenses.

Non-viable solutions:

  • Attempt to obtain a replacement clear filter online. Filter sets available for sale consist only of the colored filters. Likely people are selling the colored filters, but keeping the clear filter for use with another copy of the lens.

  • Obtain a broken copy of same lens for replacement parts. Most lenses being sold for parts are "broken" because they are missing the rear filter.

This question is not a duplicate of the following questions.

Owners of this lens can face cannot simply throw the filter away, as they would with the lenses in the questions above, because the filter is an essential part of the optical design.

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  • \$\begingroup\$ Does adapting it with a short adapter (eg M42 helicoid) to a low-FFD camera yield results too degraded? Is "take glass cutters, glass drills, diamond files, pliers to the glass from a larger filter until it fits the original filter mount close enough" within scope? (It's xiota, he probably will have tried anything I could come up with :) ) \$\endgroup\$
    – rackandboneman
    Jan 21, 2020 at 19:57
  • \$\begingroup\$ Also "check if you can find ancient m26.5 color filters that are not dyed in the glass, take them apart and destroy the dyed gelatin layer" \$\endgroup\$
    – rackandboneman
    Jan 21, 2020 at 20:01
  • \$\begingroup\$ @rackandboneman Lens works with a helicoid adapter that can be adjusted to shorter than normal M42 FFD. However, that solution would work only for people using digital. Film users would be stuck. Another digital-only solution is to use the yellow filter with custom WB. I was unable to find any other M26.5 filters, aside from those used by this lens. Removing and replacing the glass is what ended up happening. No need to use glass cutters because glass from a 25mm UV filter fit the filter ring. \$\endgroup\$
    – xiota
    Jan 21, 2020 at 20:28
  • \$\begingroup\$ @rackandboneman I hadn't thought about using a short adapter, since at the time the filter broke, I didn't have any. The only mount I can test shorter FFD with is M42. Subjectively, image quality does seem slightly better with the filter than without, but I haven't tested the lens to make sure. \$\endgroup\$
    – xiota
    Jan 21, 2020 at 20:39
  • \$\begingroup\$ I guess technically, the lens could be used with a film on a Leica or other Rangefinder... or with the yellow filter on B&W or Tungsten Film.... :) \$\endgroup\$
    – rackandboneman
    Jan 21, 2020 at 22:47

1 Answer 1

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Digital-only solutions:

  • Use a "short" adapter, as rackandboneman suggests. This may also work with rangefinders that have short FFD.
  • Use the yellow filter with custom white balance.

Solutions that will also work with film:

  • Black and white photography with the colored filters.

  • Repair the filter using glass from an appropriately sized UV filter.

    • The glass from a 25mm filter should fit without requiring any cutting.
    • The original glass appears to have been glued in. Wear appropriate eye protection when removing the shattered glass. Use an elastic polymer or contact adhesive to attach the replacement. Avoid cyanoacrylate, resins, and paper/wood glues.
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  • \$\begingroup\$ Are contact adhesives not usually very much resin based formulae? \$\endgroup\$
    – rackandboneman
    Jan 24, 2020 at 16:40
  • \$\begingroup\$ I don't know what contact adhesives are made with. To use the ones I'm thinking of, you put a thin layer on each surface then press them together. It's easy to control where they're applied. The resins I'm thinking of have two components that you mix prior to use. They're messy and likely to get on surfaces where they aren't wanted, like the middle of the filter glass. \$\endgroup\$
    – xiota
    Jan 24, 2020 at 18:51

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