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3rd cam on manual diaphragm lens?


gvaliquette

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Hello all:

 

I just saw this lens advertised on e-Bay:

 

Leitz 400 mm Telyet R lens in great shape. - (eBay item 330194437474 end time Dec-05-07 11:52:33 PST)

 

The seller states that the lens has a "third cam". Since this is a manual diaphragm lens, I thought it should have NO cam! Am I right? Should a manual diaphragm lens have cams? What purpose would they serve?

 

Thanks for your replies.

 

Guy

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James:

 

I know, 1-cam: Leicaflex; 2-cam: Leicaflex, Leicaflex SL and SL2; 3-cam: Leicaflex, Leicaflex SL, Leicaflex SL2, Leica R3-R9; 3rd-cam: Leica R3-R9.

 

The question is: the lens referred to above should be a NO-cam, should it not, or am I mistaken.

 

 

Andy:

 

Does your lens have ANY cam?

 

Guy

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The 400 is a superb lens.

 

The lens was fitted with the "3rd" cam from the introduction of the R3.

 

I'm glad it will work fine without the cam as Andy says.

 

The one that was stolen from me had the cam and worked fine as well.

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I knew it had to do with metering, but didn't know the details.

 

When the R3 came out (first Leica with automatic exposure, and the first to require the 3rd cam), Leica began adding the cam to all accessories that connected to the lens opening.

 

That includes extension tubes and bellows, which (like the Telyts) were non-automatic-diaphragm devices.

 

--HC

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I knew it had to do with metering, but didn't know the details.

 

When the R3 came out (first Leica with automatic exposure, and the first to require the 3rd cam), Leica began adding the cam to all accessories that connected to the lens opening.

 

That includes extension tubes and bellows, which (like the Telyts) were non-automatic-diaphragm devices.

 

--HC

 

If I understand it correctly, the R series of cameras meter with the lens wide open. Therefore, the camera has to be told what the working aperture is going to be when it is subsequently stopped down by the automatic diaphragm at exposure, in order for it to be able to calculate the appropriate correct shutter speed, and I think this is what the third cam does.

 

However, in the case of manual diaphragm lenses, with no auto stop-down diaphragm, the only way to meter is to do so at the actual working aperture itself. In this case, something has to tell the camera to make no allowance, that is to say, to tell it that the metering aperture is the actual working aperture. For this reason, manual diaphragm lenses have a vestigial fixed "static cam" to tell the camera that the stop-down compensation is zero. The PC Super Angulon shift lens is yet another example. It's only a simple looking bit of metal that, on a quick look, one might not think of as being a cam at all.

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John--

Thanks for the further fill-in.

 

Andy--

You don't suppose Leica told the rest of us that we needed the '3rd' cam and missed telling you?

 

I mean, what if we didn't really need the cam but Leica stood to make good money if everything got a cam? Heaven forfend! :)

 

--HC

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... I mean, what if we didn't really need the cam but Leica stood to make good money if everything got a cam? Heaven forfend! :)

 

Some R bodies need it, some don't. My R4-series bodies need +1.5 stops exposure compensation to meter correctly with an un-cammed lens.

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The third cam is also useful in other manual equipment, such as bellows. I have made my own little cam and just glued it into my Novoflex bellows - works well. But, I have found a rather curious sentence in the third edition "Leica R" book by Gunter Osterloh (German edition), where he states that under certain circumstances the lack of a third cam MAY lead to damage to the camera body. In his earlier editions, he says that the lack of a third cam would not damage either the camera or the lens. Anybody know why?

 

Kind regards, Martin

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  • 8 years later...

The third cam is also useful in other manual equipment, such as bellows. I have made my own little cam and just glued it into my Novoflex bellows - works well. But, I have found a rather curious sentence in the third edition "Leica R" book by Gunter Osterloh (German edition), where he states that under certain circumstances the lack of a third cam MAY lead to damage to the camera body. In his earlier editions, he says that the lack of a third cam would not damage either the camera or the lens. Anybody know why?

 

Kind regards, Martin

 

What is the answer to Martin's question of the variance in either damaging the camera bodies or not??  Anyone know for sure?

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