Re: [Leica] RE: 75mm f1.4 DOF

["Tom Schofield" <tdschofield@email.msn.com>]

The 100 APO macro may not be the best example because, if my recollection
serves, the focal length shortens as you focus closer, like the 105 Micro
Nikkor -- sort of a zoom-like function.  At 1:2 I believe the 100 is more
like 70mm focal length.  Also, remember marked focal lengths are an
approximation and any test treport usually specifies the actual focal
length.  The older Leitz lenses had numerals printed to the other side of
the infinity setting, that specified the correction to get the actual focal
length.

Tom Schofield

- ----- Original Message -----
From: Jacques Bilinski <jbilin@axionet.com>
To: <leica-users@mejac.palo-alto.ca.us>
Sent: Wednesday, December 01, 1999 5:13 PM
Subject: Re: [Leica] RE: 75mm f1.4 DOF


>
> >A 50mm lens at f/1.4 focused at 10 feet has from 9'7" to 10'5" in focus.
A
> 100mm lens at f/1.4 focused at 20
> >feet (exact same image size on the film as the 50mm example),
>
> >Jim
>
> >
> > No, by magnification, what I mean is that a 50mm showing the subject at
> the
> > plane of focus of 1/2 life size is going to be X inches from the
subject.
> A
> > 100mm macro lens at 1/2 life size is going to be 2X the distance.
>
> >Eric
>
>
> These statement are in themselves approximations. You can determine that
> with basic high school trigonometry. But those who are more comortable
> gleaning their beliefs from voices of authority can refer to page 52 of
the
> New Leica R8 sales brochure by Leica Camera AG, Germany. (what better
> authority could there be :) )
>
> Angle of view of the 50mm Summicron R - 45 degrees, Angle of view of the
> 100mm Apo-Macro-Elmarit-R  - 25 degrees.
>
> 45 = 2 times 25 (approximately).
>
>
> > To say that it is an approximation shows a lack of
> > understanding of the nature of optics.
>
>