This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Multi-Speed Shutter. A new form of between-the-lens shutter has been recently placed on the market, which gives the photographic worker one of the very highest types of shutter obtainable. Owing to its mechanical construction and to the form of the leaves of the shutter, this instrument will give the very best of results working between-the-lens and doing the fastest work for which the focal plane shutter has heretofore been absolutely necessary. In addition to this the manufacturers claim that on the highest speed this shutter gives three times as much illumination as the focal plane shutter, allowing speeds of 1-2000 of a second even with the largest size shutters. This shutter is known as the Multi-speed Shutter. Photographs made with it are reproduced in Illustration No. 51.
706. The range of speed for the fast exposures is from 1-200 of a second to 1-1000 of a second. For the slow instantaneous exposures the range is from one second to 1-200 of a second. The slow instantaneous studio exposures can be regulated from 1 to 6 seconds, as required by the operator.
707. The peculiar instantaneous movements of the shutter blades increase the definition of the lens over 100 per cent. This is due to the fact that it is absolutely unnecessary to stop the lens down with this shutter, while with any other type it is necessary to use a much smaller aperture to secure the same amount of definition, which would mean a great loss of illumination.
708. The shutter has only one spring for all of the different exposures, and is always ready for a new exposure without being open for resetting. In general construction the principle of this shutter is compound in the true sense. The spring is subjected to two strains, bending and twisting. Both of these strains grow in increasing ratio, so that a very weak spring on the highest tension is a very powerful motor for a shutter movement.
709. The movement of the four blades is again compound. Starting in an almost straight direction they are thrown over very quickly and settle in a straight direction, having changed their position in the shutter altogether. This straight starting and setting bring all strains right to the restrengthened centers of the blades, and regulates the definition and illumination through slow opening and setting and quick full exposure. The same ratio in exposure is kept for speeds of several seconds or 1-2000 part of a second.
710. The shutter opens from the center of the lens, with an increasing star shaped opening. The blades expose full in the middle of the movement and close again from a different point of the circumference of the lens aperture. In this way the circumferential rays are allowed to act longer on the sensitive plate than the rays at the center.
The exposure excess, therefore, appears as a maltese cross laid diagonally.
711. The results are that the corners of the plate are longer exposed than the center, thus absolutely counteracting vignetting even on wide angle work on large plates and at highest speeds. This shutter is one of the most excellent all around instruments of the kind obtainable, as it is equally well adapted to landscape and interiors, also for moving objects requiring the highest speed efficiency of the shutter.
SOME BEGINNERS' NOTES ON INSTANTANEOUS
712. Noise and speed are not necessarily connected. A. shutter may make a loud bang, and yet not be as fast as one which works almost noiselessly.
713. One of the essentials of a truly high speed shutter is lightness of the moving part.
714. Some shutters are set by a cord, which hangs loose until the shutter is liberated. If the cord is allowed to catch in anything - and the wind may blow it where it will be caught - the exposure will be spoiled.
715. For hand cameras the pneumatic release is rarely an advantage; in fact it increases the risk of movement. With a camera on a stand it is exactly the reverse; there is much less chance of shaking it when the bulb and tube are employed.
716. A shutter that fits on the front of a lens should have its opening wider than that of the hood, particularly if the shutter is a thick one. If not, the shutter will not fully uncover the lens.
717. No shutter actuated by a spring should be put away for any length of time with the spring in a state of tension.