Summarit 1.5/50 - what does the R mean in the depth of field scale?

[michaelbrenner]

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I've been researching all over and am unable to determine what the R means on the depth of field scale on the Leica/Leitz Summarit 50mm 5cm f/1.5 lens.  This particular lens is LTM / screw mount, but it also comes in the standard M Mount.  I used to have the M mount version and as I recall this R mark was on it also.  Do any of the old hands know?  Curiosity is killing me ...  

 

The R is located to the right of center, just to the right of 1.5, between 1.5 and 4.  Above the R is a thin line seeming to indicate a measurement mark with a thick black perpendicular line almost seeming to indicate a second point of focus?  Maybe for infrared photography?  I don't know anything about infrared photography, so purely speculation on my part.  

 

Any help would be greatly appreciated in solving this mystery.  Thanks in advance.

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[thomas_schertel]

It is for infrared films. You have to correct the rangefinder-measure, if you are using such films:

eg: you are measuring 10 metres, then you turn the 10 metre.mark of the lens to the red dot.

This is necessary, because the infrared light rays are Meeting on another Point than visible light.

 

yours sincerely

Thomas

[luigi bertolotti]

... you can find the "R" in lot of other Leitz lenses... the meaning is always as above.

[michaelbrenner]

Thanks for the info.  Much appreciated.