[rollei_list] Re: 2.8F opton?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sun, 6 Jul 2008 22:11:15 -0700
----- Original Message -----
From: "Carlos Manuel Freaza" <cmfreaza@xxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Sunday, July 06, 2008 8:20 PM
Subject: [rollei_list] Re: 2.8F opton?
I think it is relevant for this case Eric because a built-in
central shutter in the lens need a lot more room than a
simple iris used for the Biometar 2.8/80. The Hasselblad
lens has shutter blades+shutter mechanism +iris, the
Biometar for the Pentacon has iris only, it could make a
significant difference (according the lens FL)despite both
cameras have the mirror box between the lens and the film
plane.-
Carlos
The shutter blades and diaphragm of most shutters takes
very little space. They lie nearly touching and are very
thin. It is possible that some very short focal length
lenses might not have a wide enough air space to accomodate
both. The old Bausch & Lomb Volute shutter used the same
blades as both iris and shutter blades and could be used for
some lenses with exceptionally small air spaces for example
the Zeiss Extra Wide Angle Protar in very short focal
lengths.
A lens of about "normal" focal length may not need to be
of the retro-focus type to have a long back focus. There are
design considerations in many lenses which will allow some
increase in this distance without the special design. An
elementary example is an ordinary single meniscus lens which
has its principle planes displaced in the direction of the
curvature. When mounted with the concave side facing the
subject the lens is slightly retro-focus and is slightly
telephoto when mounted the other way.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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