[rollei_list] Re: Tripod versus Handheld
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Thu, 18 Aug 2011 13:38:02 -0700
----- Original Message -----
From: "CarlosMFreaza" <cmfreaza@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, August 18, 2011 12:29 PM
Subject: [rollei_list] Re: Tripod versus Handheld
2011/8/18 Don Williams <dwilli10@xxxxxxx>:
At 10:01 AM 8/18/2011, Alan wrote, in part:
I remember something about a glass accessory plate for the
Rollei. Did that
go in front of or behind the film?
My recollection is that it went in front because I had
some concerns about
scratching the film. Never saw one, though.
Most Rolleiflex TLR cameras (except the T) made from 1960 to
1966 were
prepared to receive a glass plate or "Planglass" to assure
film
flatness when film was in the film plane position, the glass
was
placed in front of the film and it required a dedicated
camera back
with a third position for the film pressure plate. Some
tests
demonstrated there was no significant or visible image
quality
improvement even for big enlargements sizes, the glass use
had
problems with dust and humidity and fingers marks recquiring
often
cleaning and then Rollei no longer manufactured it from
1966.
The Rollei SL 66 "bible" advises -if possible- to advance
the film
only a few seconds before to shoot the camera, this way the
film paper
back has no time to modify the film flatness on the film
plane. The
220 film has no paper back and then it avoids this problem.
Some Carl
Zeiss tests showed a significant sharpness difference for
120 and 220
film (220 film was better) due to the 120 film paper back
action on
the film strip.
Carlos
---
I have never been completely satisfied with my
understanding of how the film is located in either roll film
or 35mm cameras. In both the Rollei and my Leica and Nikon
the film runs in a channel between the guide rails. The
channel is just thick enough to accomodate the film (or film
and backing paper for roll film). The back plate does _not_
apply pressure to the film despite its often being called a
pressure plate. In Rollei cameras with back plates which are
adjustable for the Rolleikin attachment the distance of the
plate from the film gate is changed making the channel
narrower for 35mm film. It seems to me that the film plane
must be established by the back plate and that the film is
supposed to relax against it rather than being tensioned
against the front of the film gate. Despite this the focus
adjustment is usually made by inserting a ground glass
located by the gate. The difference is exteremely small. I
don't have the instruments to measure it. I suspect it would
be done on a camera with the lens removed and using a
precision depth micrometer or optical depth micrometer. The
factory evidently used an auto-collimator with a plane
mirror that fitted against the inside of the film gate,
again using the gate to determine the film plane but I am
not sure this is how things work in practice. There are
cameras that have actual pressure plates; many motion
picture cameras work that way, but I think few still
cameras. Sheet film cameras definitely use the back of the
film holder to establish the film plane.
Something else: I discovered that some Rollei lenses,
certainly the Tessar types, have some focus shift. Not a lot
but there will still be some change in the precise point of
best focus as the lens is stopped down from maximum
aperture. I think this is mostly masked by depth of focus as
its stopped down. This is a problem with any camera which
focuses by means other than direct observation of the image.
Since most SLR cameras focus with the lens wide open and
stop it down for the exposure they are vulnerable to the
same error.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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