[pure-silver] Re: Pre-soaking film
- From: harry kalish <hksvk@xxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 01 May 2010 18:34:02 -0400
Responding to Eric¹s message: DITTO. Thanks, Richard.
On 5/1/10 1:38 AM, "Eric Nelson" <emanmb@xxxxxxxxx> wrote:
> Thanks, Richard, I had always wondered about that!
>
>
> From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
> To: pure-silver@xxxxxxxxxxxxx
> Sent: Fri, April 30, 2010 10:26:19 AM
> Subject: [pure-silver] Re: Pre-soaking film
>
> Roll film has to be quite flexible because in many cameras it must make
> fairly sharp turns. 35mm film OTOH, usually follows a fairly straight line
> from supply to take up spool. Sheet film is the thickest because it has to
> stay flat in film holders. Now, film pack film was on the same support as roll
> film because it had to be flexible to work in the film pack where it is pulled
> around to the back when changing films.
> 35mm film was designed originally for use in motion picture cameras and
> projectors where it is subject to considerable strain so must be strong and
> resistant to tearing.
> The support thicknesses have not changed much in many decades but emulsion
> thickness has. One reason for the much improved resolution of modern films is
> the reduction of "irradiation" or scattering of light within the emulsion
> mainly because the emulsions are thinner. Since the emulsion is a fraction of
> the thickness of the total film thicknes this does not make much difference to
> the overall thickness.
> Film flatness is determined by several factors, not least of which is the
> camera design. In both roll film and 35mm still cameras the film is located
> mostly by the back plate. Right after the film is wound it may be held taught
> between the guide rollers but soon it relaxes so that the film or backing
> paper of roll film lies against the back plate. Although back plates are often
> called pressure plates they exert no pressure on the film. Rather they create
> a narrow channel between the plate and guide rails that the film runs though.
> In Rolleiflex and Rolleicord cameras the back plate is located by little tabs,
> or what I call feet, that rest on machined reference surfaces next to the
> guide rails. The shifting plate in later cameras serves to adjust the
> thickness of this channel for either 35mm film or 120 roll film with paper
> backing. An examination of the back plate will find that some have two sets of
> "feet" of different lengths which are brought to bear on a common reference
> surface pad or that there is a single set of feet and two reference pads of
> different hights. The shifting of the back plate also moves it out of the way
> of part of the Rolleikin but the main purpose is the channel thickness
> adjustment. 220 film, because it has no backing paper should require a
> narrower channel to properly locate the film although the difference may not
> be enough to affect focus significantly.
>
> --
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
>
>
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