|Roller Blind Shutters|
|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.
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