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What is 7p?
I see the list is a bit slow tonight (Gabriel must be out for dinner...;))
So, let me answer a basic question:
What's the big deal? (What is 7p and why am I so excited?)
It is this issue of format again (another of my favorite topics).
Depending on their width (across the length of the film), we can classify
35 mm images into these common categories:
- 4p (half-frame, Nimslo, etc., 18 mm width, portrait)
- 5p (Realist format, 23 mm, squarish)
- 7p (European format, Belplasca, Verascope, FED, 28 mm, landscape)
- Full frame (36 mm)
The p number refers to the number of perforations (or sprockets) of the
35 mm film (those holes at the edges) included in one frame. As we go
down in this sequence the width (or length) of the image increases
while the height remains the same (appr. 24 mm)
A 7p frame is wider than the 5p and lets you see more in the horizontal
direction. For years I have been an avid supporter of the 5p (Realist
format). It works well for a number of subjects and it is the optimum
size for handviewing and projection, in the sense that it can be
magnified the most in a square projection screen (usual size of
commercial projection screens) or through a round lens.
My first experience with the 7p format was when I mounted a twin SLR
hyperstereo (clouds shot from a moving car from the ground!) into a 7p
mount. I then proceeded taking single camera hyperstereos and
eventually electrically connected two SLR cameras for more extensive
twin SLR work.
One of the first problems when dealing with 7p images was that my
favorite Realist red button viewer would not show the entire 7p image.
Not only that, but it also distorts the nice stereo window that I put
into the image by carefully spacing the two chips in the mount. This
is happening because the cropping of the 7p image by the viewer's
apertures is not symmetric (that's not the case for other viewers,
for example the Realist green button, where the cropping is symmetric
and the 7p is cropped but the correct window placement in maintained).
This problem led me to modify my red button viewer by enlarging the
apertures for 7p viewing. This and other custom modifications of
this viewer ended up in my first viewer book (on the red button,
published in 1994) and eventually resulted in my current viewer
custom modification & repair services, supplies, etc.
The procedure I follow to mount full-frame pairs from my SLR cameras
is to first I use a 7p mount, inspect the image and, if satisfied,
leave it in 7p. For compositional reasons I occasionally used 5p
mounts. I enjoyed the wider 7p size in my modified Realist viewer
but I still had my heart set in the Realist format and enjoyed
using my Realist for most of my stereo photography.
(To be continued with focus on projection...)
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