[rollei_list] Re: Do you know?

  • From: Frank Dernie <frank.dernie@xxxxxxxxxxxxxx>
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Sat, 10 Jan 2009 10:45:03 +0000

Hi Carlos,
One has seen several comments about rangefinder base length over the years. It is certainly an important aspect for potential rangefinder accuracy but the precision to which all other parts are made, such as the lens register to film plane accuracy, lens mount to focusing cam accuracy, and the precision of the internal mechanical parts linking the lens focus movement to the optics of the rangefinder are equally important. The classic example of getting this wrong is the Kodak Ektra. This has a huge rangefinder base but the mechanism connecting it to the lens movement is pitifully inadequate and prone to wear such that it is extremely unlikely for a used Ektra to be nearly as accurate in focussing as a Leica, despite the potential of the rangefinder base.
Frank


On 9 Jan, 2009, at 08:50, Carlos Manuel Freaza wrote:

I think the word "telescope" was confusing Richard, however later Leica SM models have viewfinders with 1.5x magnification, being the baseline physical length about 38mm x 1.5= 57mm for the effective baseline, shorter than the Contax II effective baseline clearly, anyway a good effective baseline for focusing. I have the book "35 MM Photo Technique" by H.S. Newcombe, it shows the Contax and Leica SM and Ektra rangefinder designs, they are pretty different (the Ektra has a "split field" RF type).The author writes the cameras physical baseline length only, not the effective baseline. The two wedges in the Contax RF are significant to keep the RF calibration even for worst situations.

An interesting comparison about the new Zeiss Ikon RF and Leica M7:

Zeis Ikon RF
75mm x 0.74 magnification with an effective length of 55.5mm

M7:
69.25mm x 0.72 magnification, with an effective length of 49.9mm.

"...prewar Contax of Zeiss Ikon AG were always superior to Leica. Indeed, the Contax was known, thanks to its long rangefinder baseline, for the highest accuracy in measurement of object to camera distance for precise focusing." (Shutterbug, S.Takeda, April 2005)

Carlos



--- El jue 8-ene-09, Richard Knoppow <dickburk@xxxxxxxxxxxxx> escribió:

   Well, you are right, I just looked again. The range
finder image is larger because it is life-size while the
viewfinder has some reduction in size.
   While the Contax has metal slats in the shutter I am
not sure it is safe to point it at the sun due to the cloth
ribbons that hold the slats together. Even an all-metal
shutter curtain such as the one used in Nikon F cameras is
probably not immune to sun damage. Of course, in an SLR with
an automatic mirror return the shutter is exposed to the
outside world only briefly so it isn't really
comparable.
   As far as noise, I don't know of any focal plane
shutter which is as quiet as a Compur shutter.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---



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