SCIENCE- G OSSIP. 



217 



shutter should at least answer these two essential 

 properties ; we therefore propose to give a descrip- 

 tion of the various types of shutters now before 

 the public. 



The Koller-Blind Shutter is undoubtedly 

 the most popular ever put on the market, and for 

 years was made solely by the Thcrnton-Pickard 

 Manufacturing Company. Now it is made by 

 many firms in various forms. The principle of 

 this shutter consists of an opaque blind in the 

 centre of which is an opening : this opening is made 

 to pass rapidly across the front or back of the 

 lens, so exposing the plate. The speed at which 

 this blind travels varies according to the strength 

 of the spring roller, which can be regulated to the 

 required exposure. These reliable blind shutters, 



Roller Type of Shutter. 



as a rule, open every time the shutter is set. 

 They are, therefore, more suitable for stand 

 cameras than for hand cameras. For time ex- 

 posures the blind can be arrested midway and 

 prolonged exposure given. The Thornton-Pickard 

 shutter has an indicator fixed to it which indicates 

 the exposure given. The firm also supply a time- 

 value, if required. With this addition the shutter 

 is universal in its use, being capable of giving 

 short time exposures of \, \, J, 1, 2, and 3 seconds. 



The " Diaphragm " Type of Shutter is 

 generally constructed of metal throughout, and 

 the exposure is made *by the movement of metal 

 leaves actuated by a spring, the opening and closing 

 of which exposes the plate. The speed at which 

 these leaves move is governed by a pneumatic 

 arrangement. Thus speeds varying from ^th to 

 3 seconds can easily be obtained. These shutters 

 do not open when setting, and, as a rule, they are 

 supplied with either finger release or with a pneu- 

 matic ball attachment. Of this type of shutter 

 the best known are the " Bausch and Lomb 

 Diaphragm" shutter, the " Unicum," the Goerz 

 "Sector," the " Lopa," and the Thornton-Pickard 

 " New Iris " shutter. 



The " Focal-plane" Shutter is one that has 

 come very much to the fore of late, and seems 



likely to stay with us. This is also a blind shutter, 

 but instead of working on the lens it is placed 

 immediately in front of the plate. The blind has 

 a variable slot, which is caused to pass rapidly 

 across the plate, thus exposing the picture thrown 

 upon it by the lens. The amount of exposure is 

 governed by the size of the slot and by the tension 

 of the spring. These are very high-speed shutters, 

 the exposures obtained by their use varying from 

 Y^gth of a second to g^th or ^th of a second. 

 When this shutter is used for hand-camera work 

 some means must be devised for covering up the 

 lens whilst setting the shutter, otherwise it will 

 expose the plate during the setting. 



The Flap Shutter is one that is used almost 

 exclusively by professional photographers for studio 

 work, and is best known as the "Guerry." The 

 principle is a simple velvet flap, which opens and 

 closes by means of a pneumatic ball. When the 

 ball is pressed the flap is raised, and when the ball 

 is released the flap falls, thus concluding the 

 exposure. It is a most useful shutter where quick 

 exposures are not required, and is very silent and 

 effective. 



Foreground Shutters. — Thereiis another class, 

 known as the " Foreground " shutters. To these 

 we have already referred when writing on the 

 " Window-blind " and " Flap " shutters. We have 

 also had the opportunity of testing one known as 

 the "Adjustable." This is a metal shutter in 

 which the exposing portion is raised in front of 

 the lens and returns again to complete the expo- 

 sure, thus giving considerably more exposure to 

 the foreground than to the sky. The rate of speed 

 at which the exposing piece travels is governed by 



Diaphragm Type of Shutter. 



means of a pneumatic piston, and the exposure 

 can. be regulated from s l 5 th to a second, and also 

 time can be given. 



There are many modifications of these different 

 types of shutters, but they are all more or less 

 alike. Given the class of work the shutter will be 

 required to do, there should be no difficulty in 

 selecting from the foregoing description the most 

 suitable type for any purpose. 



(To he continued.') 



