[rollei_list] Re: Tripod versus Handheld

Several Rolleiflex TLR manuals indicates the exact focal plane or film
plane location, it is the white or bright line in the camera body in
contact with the camera back when it is closed, the 2.8C manual says
:"32 Focal or film plane (focusing distances measured from this
line)". The film channel is formed with the contact between the
four/eight little tabs in the  film "pressure plate" and the four
little metal plates beside the film guides, these little plates are
deeper than the film guides slightly, coinciding with the tabs or feet
"height", this way the film runs with its  _edges__ hardly pressed
between the film guides and the pressure plate keeping or trying to
keep the film flatness. The film is placed and runs along the film
plane coinciding with the line shown in the manual.

Carlos

2011/8/18 Richard Knoppow <dickburk@xxxxxxxxxxxxx>:
>    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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