Bruce wrote:
"K W Hart" wrote:

Absolutely. The fastest shutter speed of a horizontal travel shutter
is 1/2000 sec with the titanium foil shutter of the Nikon F3, but most
other cameras with horizontal travel shutters can only manage a
fastest shutter speed of 1/1000 sec, and may not even manage that
unless they have recently been serviced.

That's a design issue. The maximum shutter speed of a focal plane shutter is
a combination of how fast it travels and how wide the gap is between the
first and second curtain.

The travel time is noted by the maximum sync speed, how fast the curtains
travel, one frame width apart, so that the film is uncovered entirely
during exposure.

Bear in mind that a horizontal shutter has to cover 36mm, while a vertical
one only has to cover 24m. So our 100th of a second horizontal shutter has to
run at 3.6mm/ms while our vertical one has to run at 2.4mm/ms. Using that
notion, the usual 1/250th flash sync shutter runs at 24mm/4ms or 6mm/ms.

At 6mm/ms, that would make our horizontal shutter have a top speed of
6ms or 1/166th second flash sync speed. For easy arithmetic, let's round down
to 1/150th.

So if we cut the frame in half (second curtain follows first 18mm behind)
that would be 1/300th top speed, 1/4 (9mm) 1/600th, 1/8 (4.5mm) 1/1200th,
1/16th (2.25mm) 1/2400th, 1/32 (1.25mm) 1/4800, 1/64th (.612mm) 1/8800th.

The limitations of doing this is, you can't keep reducing the size forever,
eventually it becomes too small to be a shutter, and becomes a long pinhole.
The other is that no shutter is perfect, there will be small variations in
angles of the curtains, smoothness of travel, speed, etc.

The wider the gap between curtains, the less these things affect the
photograph.

The horizontal curtains are much bigger, they are several that cover a
vertical frame, each 36mm wide, but much shorter in height. A horizontal
shutter needs to have each curtain be at least 24mm high and 36mm wide,
probably much wider. Bigger curtains mean more weight, which means more
inertia, which means more force to move.

The advantage of them is that you have all that room to work. A vertical
shutter has to sit between the viewfinder and the bottom of the camera, a
horizontal one has to fit between the casette and the take up spool, and
they can be easily moved farther apart if needed.

I think it is all accademic, as I doubt that anyone is going to design a
totally new film camera for a long, long time. They more likely are going
to take an existing design and modify it, such as all of those variations
of the Chinon SLR, which also includes the Voightlander rangefinder cameras.

As for digital cameras, I really am not sure why one actually needs a shutter.

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count. :-(