Leica R lenses in Canon or Nikon mounts ?

This has got to be one of the most commonly asked questions: "Why don't Leica offer versions of their R lenses in Nikon or Canon mounts? Surely they would sell thousands of these things!"

Indeed they would — and that is the problem. As remarked by veteran photojournalist Sal DiMarco Jnr in August 2002:

Every few months someone suggests Leica make lenses in Canon and Nikon mounts. Well, Leica had talked to both Canon and Nikon and they both declined. This came out of the mouth of a VERY highly placed Leica AG executive. So, I feel confident it's not going to happen. Yes, there are other off-brand manufacturers of Canon and Nikon lenses but their stuff is considered inferior. Leica lenses wouldn't be. Think about it…

Say what you will about their plastic camera bodies with fifty-thousand too-many-features, but the people at Nikon or Canon aren't stupid. Release the Leica R19mm or R100mm APO in F or EOS mounts and sales of the camera-brand equivalents would crash.

In August 2005, Douglas Herr spelled it out in more detail:

David Young wrote:
> … I tend to agree with the Luminous Landscape… If
> Leica were to build their lenses in Nikon/Canon mounts,
> only a very tiny percentage of those owners would ever
> buy one. But it would probably double Leica's lens
> sales! And lenses (not cameras) are where the money is!
This topic has been discussed a number of times on several forums. In a nutshell:
If you want auto-diaphragm and full-aperture metering, there are two paths to this: co-operation and reverse-engineering.
Co-operation won't happen, period. Canon doesn't want the competition. The interest in using Leica-R lenses isn't miniscule. Go to the Fred Miranda forum and see how much discussion there is on the subject.
Reverse-engineering is risky, because Canon can (and has) made minor firmware tweaks that "break" the compatibility of third-party lenses. As a lens purchaser you might be willing to take that risk if the lens offers you a significant discount but are you willing to bet the price of a Leica lens that it won't be turned into a doorstop? I don't see a market here.
Foregoing the auto-diaphragm and full-aperture metering would be using the Leica lens in full manual mode, exactly like using an R-mount lens with an R-to-EOS adapter. A manual-only lens in an EOS mount would lose the flexibility of using it on a Leica-R body. I don't see a market there either.
Ditto for Nikon mount, with the possible exception of an AIS mount, except that many current Nikon bodies treat AIS lenses as though they're manual-only. Can't even use the camera's meter.

So if you want to mount a R lens onto a "Canikon", then you have to do it the clunky way via a lens-mount adapter ring or — more drastically — lens-mount flange surgery.