[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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