Convert Canon breech mount to newer bayonet

I maybe would have understood rebuilding a lens from BL to FDn, but these days only the time invested in thinking about such a rebuild cost more than simply buying an FDn lens. Just buy the one you have in BL in FDn and be done.

Well there is actually a very easy way to convert, at least for more common lenses.

 

First you sell the one you have, then you buy the one you want.

It might even be that some collectors would rather have the older one, so you

might be able to do it as a trade.

 

Used manual focus lens prices are pretty good by now, and it will be a lot less expensive

than even one tool that you would need for any possible conversion.

Each version has its advantages.

 

Influential magazines of the day widely considered Canon's breech lock the most technically sophisticated 35mm mount of the era, because it combined the speed of bayonet mount with the custom-each-time snugger fitting of M42 screw mount.

 

But like many "perfectly engineered" creations, it faltered somewhat at the human interface level. While Canon did cleverly integrate a self-starting breech, this did not overcome the fiddly aspects of mounting the lens with no tactile (and limited visual) feedback, so more often than not a lens would fail to engage self-start and simply fall out of the mount. While a minor occasional nuisance to enthusiasts and pros, this was a total PITA for the utterly inept amateurs who began flocking to SLRs in the mid 70s (lured by the heavily-misrepresented marketing of AE and winders and sports celebrities).

 

After Nikon finally rid itself of its cumbersome pin-and-prong lens coupling in 1977 with AI, and Pentax' earlier heavy promotion of its transition to bayonet from M42, Canon no longer had any competitive cover for the quirks of its own breech lock system. Combined with the exploding sales of its consumer-oriented AE-1 camera, Canon was left with no choice but re-engineer the breech ring into a goof-proof quasi-bayonet system. In this they succeeded remarkably well, but a lot of Canon fans still prefer the breech system operation. Also the lower-end non-pro breech lenses were of classic-era uncompromising build quality, while the many of the FDn revisions became increasingly plastic.

 

Other than Canon in 35mm format, two medium format systems, Mamiya Press rangefinder and Kowa 6 SLR, employed breech lock mounts. These were much larger and slightly cruder than Canon's (no spring loaded self-start, breech ring on the body instead of each lens). The Press is a bit fiddly but fairly simple once you get the hang of it. The Kowa needlessly saddles you with an infuriatingly balky fingernail-shredding breech ring release lever, which defeats the whole purpose of having a breech mount.

KW's Praktina 35mm single lens reflex also used a breech mount system for its lenses, and it preceded any of the Canon SLRs to do so by several years.

The USSR Start SLR had a breech lock mount, but only the 50mm lens was ever made for it.

 

The Start - the "USSR Exakta"