M-mount Lens question

[Pirate]

What are the "Cams" when talking about these lenses?

I was looking at B&H photo's used Leica lens section and they mention some lenses with One Cam, Two Cam, and Three Cam.

Can someone please explain this to me?

And does this also apply to the R-system?

Thanks

 

[elmer3.5]

R

R

Hi, cams are for R-system, they are used to set different functions on early and late R leicas.

M lenses have cams but to display the precise frameline you need on particular lens.

Bye.

 

[Tom A]

It only applies to the R-system. The first R-lenses for the Leicaflex Standard had one cam (it transferred the f-stop information to the cameras external meter.
Later with the Leicaflex SL/SL2 they were equipped with 2-cams (same information, but a different meter-system, through the lens.
The 3 cams were for the later Leicaflex's - the R5/R6/R7 and also the R4. The R3 used a slightly different system and R3 lenses sometimes dont work on the rest of the bodies. The R8/R9 had electrical transfer of information - basically "chipped" lenses.
You can have 2 cam lenses converted to 3 cam etc. Single cam can be converted, but it is expensive - considering the value of the lens.
It is a bit bewildering, but as the system is more or less backwards compatible (i.e a 3 cam lens will work on a SL/SL2 and in most cases on a an old Standard too).
On the M-lenses you also use cams for focussing information, either a circular "tube" with a curve on it - or a sliding "bar" that engages the focussing roller.

 

[Pirate]

Got it. So if I see a used Leica lens that says it's a 1-cam, 2-cam, 3-cam... I should realize it's for an R-system.

Thanks!