I have been wanting something like this for ages (wide angle converter that's behind the lens)

Started Jan 14, 2013 | Discussions thread
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Joseph S Wisniewski
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Re: Making it retrofocus is illegal, LOL
In reply to Gerry Winterbourne, Jan 18, 2013

Gerry Winterbourne wrote:

Joseph S Wisniewski wrote:

Gerry Winterbourne wrote:

It's clear, therefore, that it would be feasible to design a version of this adapter that would include some retrofocus capability to allow for the small projection it would need in front of the body.

There are four problems with doing that.

  1. Kodak has a patent on retrofocus wide converters that they have been loath to license.
  2. Fast retrofocus optics are expensive. Price a 24mm f1.4 or a 35mm f1.4.
  3. Fast retrofocus optics are big. A non-retrofocus 24mm f1.4 can be packed into a cylinder about 30mm long, 25mm wide. The retrofocus Nikon is a good 25x the volume.
  4. Retrofocus stuff is hard past f1.4. Oly incorporated wide converter rear sections in their 14-35mm f2, and even optimizing it for the permanently attached 28-70mm f2.8, they couldn't get it past f2.0.

Note that I said "design" - a patent might prevent realisation of the design but not the design itself.

True. Althought optical engineering is an expensive hobby. The main motive is profit.

Incidentally, in another post you talk of the patent dealing with maintenance of back-focus distance to miss the mirror: for the K-01 there's no mirror and optics could go in the space - would that get round the patent?

Yes, but it wouldn't yield a usable device. The height of the k01 "mirrorless" mirror box is 22mm. That restricts the diameter of the optical tube to 22mm, and the maximum aperture of the speed booster to about  f2.3. It wouldn't be a speed booster.

I can't actually envisage that Pentax would think the market sufficient, but it it did I'd guess they'd design for their own range of FA lenses, which don't reach the speeds you mention here. The FF DS14/2.8 is the worst case. I accept that it probably wouldn't be commercially viable but is it actually impossible?

It would be impractical. The length diameter ratio makes the design complex, and limits speed and the ability to correct certain aberrations.

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Rahon Klavanian 1912-2008. Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed. Ciao! Joseph www.swissarmyfork.com

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