Archived posting to the Leica Users Group, 2000/08/05

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Subject: Re: [Leica] Re: 50/1.2 or 50/1.5 or 50/2?!
From: Dante A Stella <dante@umich.edu>
Date: Sat, 05 Aug 2000 16:41:29 -0400
References: <398B5013.899600FE@umich.edu> <047a01bffe6f$54299720$9133a4cb@rivrw1.nsw.optushome.com.au>

Then why wouldn't the two 50mm lenses read the same?  The differences in focal
lengths cannot explaint that one.

I don't think angles of observation matter, since I repeated the test 10 times
and always got the same results.

Maybe it's omitting 4 air-to-glass surfaces.

Miro Jurcevic wrote:

> My understanding from what I have been told about lenses, is that the light
> geometry of different focal lengths determines the F-stop for that focal
> length.
>
> Essentially, it is possible to have a different exposure for 50mm f2 and
> 85mm f2, since the f-stop is a ratio of focal length to lense diameter. The
> longer focal length is metering a smaller area of the same space and would
> in effect be metering less light per given area.
>
> Secondly, there is no similarity between the three metering systems and the
> bias toward factory settings. Unless we are using a single scientific meter
> will all four objectives.
>
> Thirdly, variations in angle of observation, even angles less than 10
> degrees, can alter the reflected angle entering the metering system.
>
> These comments are based on the physics of the scene that you have
> described. There is simply more than one variable being tested.
>
> Miro
>
> > Canon 50/1.5 @f/2 = Between 1/250 and 1/500 sec
> > Nikkor 85/2 @ f/2  = 1/250 sec
> > M-Hexanon 50/2 @f/2 = 1/250 sec
> > M-Hexanon 90/2.8@ f/2.8 = 1/125 sec
> >

- --
  ------------------------------------------------------------------------
Dante Stella
http://www-personal.umich.edu/~dante

In reply to: Message from Dante A Stella <dante@umich.edu> ([Leica] 50/1.2 or 50/1.5 or 50/2?!)
Message from "Miro Jurcevic" <miroj@ozemail.com.au> ([Leica] Re: 50/1.2 or 50/1.5 or 50/2?!)