Exposure times had reduced sufficiently by the 1880s to see the mechanical shutter being in widespread use. An early version was the roller blind type, in which a length of light proof linen with a gap cut out is attached to rollers, at each end. One roller has a spring mechanism built within it, so that it winds the blind in. The device is tensioned by pulling a drawstring attached to the other roller. When the trigger is released, the blind travels rapidly from one roller to the other - briefly allowing light into the camera as the gap in the blind passes the lens. These early shutters were often attached to the front of the camera as an "add on". An important feature of the early cameras was the common method of composing and focusing the image on a ground glass screen placed at the focal plane, where the plate (film) would be placed for the exposure. In order for this to be able to happen light had to pass through the lens, and the shutter was fitted with a stop so that the gap in the blind could be "parked" in front of the lens. Naturally, the gap had to be big enough to allow the full diameter of the lens to pass light, and it was the size of this gap that was one of the chief limiting factors of the roller blind shutter - as the only way to speed up the exposure was to speed up the blind. Thornton Pickard manufactured shutters of this type, both as slip on attachments and built onto their own camera designs. The photographs shows a Thornton Pickard roller blind shutter, in the second the front has been removed - clearly showing the two rollers.
This Thornton Pickard roller
blind shutter has the facility to alter the shutter speed by
tensioning the roller spring. Increasing the tension speeds up
the travel of the blind and reduces the time taken for the gap
to travel in front of the lens - reducing the exposure time.
The major disadvantage of this is the rather violent way in which
the blind is brought to a stop, it is very rough on the blind
and frankly any that are still working with their original blinds
will be very delicate by now - I would advise against using the
fastest shutter speed. The majority of these shutters will by
now be rather past their shelf lives, and few work with any degree
of reliability. They are, however, quite simple to rebuild, this
example was completely rebuilt in 1992 using all the original
parts except for the blind material itself. Despite the disadvantages,
the roller blind shutter can be thought of as the ancestor of
the "modern" focal plane shutter.
The advent of faster films meant that the possibility of faster
shutter speeds needed to be addressed, and a neat solution was
developed. Essentially two roller blind shutters mounted one
immediately behind the other, the clever part is that the gap
can now be altered by advancing one blind further than the other.
This removes the need to stress the blind unduly by speeding
up the travel with the consequential accelerations involved.
The two blinds now travel at the same speed irrespective of the
exposure speed, but the gap between them is altered - which means
a shorter exposure. The beauty of this is that extremely rapid
exposures can be achieved by using a very narrow gap. Mechanically
there are several variations on how to achieve this, but the
principle of the variable gap remains constant. Although focal
plane shutters were available as retrofitted assembles in a similar
fashion to the slip on type, this system is usually built into
the camera from the outset and consequently these shutters were
made by the camera manufacturer. This opens up more possibilities,
firstly the ability to change lenses without allowing light to
expose the film, as the shutter is in front of the film. This
became important with the arrival of roll film cameras with no
other facility to stop light hitting the film with the lens removed.
Perhaps more importantly it allowed the use of a reflex mirror
between the lens and the film plane with the introduction of
the Single Lens Reflex. Many will be surprised to know that the
focal plane shutter was not uncommon by the mid 1890s. The principle
remains to this day, although cloth blinds have given way to
metal ones. Apart from it's mechanical complexity, the only disadvantage
with this type of shutter is with flash photography. Because
the duration of a flash is so short, in the order of 1/10,000th
sec, the blinds have to be opened to a gap that encompasses the
whole negative - otherwise the flash would "freeze"
the blind as it traveled across the film gate. This essentially
means that many cameras fitted with focal plane blind shutters
are limited to a flash synchronisation speed of around 1/30th
sec. This can leave the photograph vulnerable to camera shake,
particularly noticeable if the flash is being used as "fill
in" on an otherwise well lit subject. The only other disadvantage
might be the noise generated, as all but the very best tend to
be a bit noisy on release.
Back to camera anatomy, or if you prefer, the foyer.