[Leica] More on Leitz Patents

["Robert Rose" <rjr@usip.com>]

In response to Gaifana and Austin:

>>I'm kind of curious to know how the M mount (or any bayonet mount) could be patented after Contax had presumably done it or introduced it to the public). 

Improvements can be patented over prior art, and that is what they did.  The two critical patents I have found so far are Wehrenfennig '581 and Brohl '201.  Wehrenfennig teaches the use of 4 lugs on a bayonet arranged so that light coming from long focal length lenses, or of high intensity, is not cut-off in 35mm cameras, and Brohl teaches the use of protuberances or notches to align the lens and camera body.

(BTW, how do I represent an umlaut in e-mail?)

Further in the 1950s more patents were secured on the coupling between the rangefinder and the lens.  So, in order to make a lens to fit the M3, several patents would have had to be considered.

>>>I know I'm looking with U.S. patent law retrospect, but that would have never flown today. 

Well, the basic patent law on this hasn't changed that much in the interim.

>>>Perhaps the only reason it was "patented" in the U.S. was reciprocity with Germany, which perhaps had weaker patent standards. 

No, I don't think that is the answer.  The patents demonstrate  novel, non-obvious improvements over the prior art.  There is no concept of such reciprocity as you suggest in patent law, beyond allowing the filing date to be extended back to the date of filing the foreign patent in some cases.

>>>By 1952, the bayonet mount was present in Contaxes and Rollei filters, both of which predate the M3.

Yes, that is correct, the existence of bayonet mounts is disclosed in the patents (as of January 1951).

>>>Of course, today, any patent today only lasts 20 years - if today's regime had been in place in the 1950s, the Leica clones would have shown up in the 1970s. 

The US patents granted in 1953 lasted 17 years from issuance.  Patents granted today last 20 years from filing (with some exceptions).  Since a patent can take 3 years to prosecute, the difference is not usually too much.

Nevertheless, your point is well taken.  The 1950 patents were gone by the 1970s.  Why did we not get clones sooner?  I am researching this.  

>>>>[Austin] My 1949 Hasselblad has a red dot on the body, and a red dot on the lense, to aid in mounting alignment.  Perhaps there is more to the patent than the red dots?

Actually, the red dots would be equivalents to the notches and protuberances taught by Brohl.  A notch on the lug is also taught.  It is hard to be sure without the file history, but it seems that Brohl was filed 2/7/1951, and claimed priority to 2/13/1950 based on a German patent filing date.  That makes the one-year critical date 2/13/1949.  Without boring everyone, a public use or sale in 1949 of the invention therefore might or might not make it prior art.  It depends :-)  Don't know, but that is another interesting avenue for further research.

Hope everyone is still awake,
Bob Rose