[pure-silver] Re: [OT] Filmholders, Septums, Total-Disasters
- From: "Michael Healy" <emjayhealy@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 23 Nov 2005 09:24:16 -0700
The septum isn't a part of the camera, it's a part of a filmholder. Any
filmholder that
holds two sheets back-to-back consists of a frame that sandwiches a thin
membrane, a
septum. This is what the sheets of film are pressed against when they're inside
the
holder. One sheet gets pressed against one face of the septum, the other sheet
against
its oppose face.
An inherent problem of design (or of manufacture and quality control) would be
that the
septum's thickness and placement must be such that both sheets of film will be
situated
precisely on the same plane occupied by the groundglass. If the sheet's plane
is not the
same as the groundglass's, then it won't rest precisely where you just focused.
Years
ago, when I built a Bender, this was the last trick I had to perform before
shooting: to
shoot a picture after focusing along a ruler at f5.6. That was to see whether
the film did
find precisely the same ruler mark I'd focused on. Turned out it was, but if it
hadn't been,
then I'd have had to adjust my groundglass with shims, and repeat until the
planes were
the same.
But I'd never heard about holders themselves being problems. Hasn't been been
my
experience, either. And half of my 4x5s were probably born before I was. In
fact, my
8x10s probably were born before my dad was!
Mike
On 23 Nov 2005 at 9:14, Scott Hamming wrote:
Subject: [pure-silver] Re: [OT] Filmholders, Septums,
Total-Disasters
Date sent: Wed, 23 Nov 2005 09:14:07 -0600
From: "Scott Hamming" <Scott.Hamming@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Send reply to: pure-silver@xxxxxxxxxxxxx
>
> Not being a LF user, yet, I wasn't aware that any camera's had a
> 'septum'. What exactly is it?
>
> Scott Hamming
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