A Practical Magazine for Photographers.
The Camera Publishing Co.
SPEED TESTING DEVICE FOR PHOTOGRAPHIC SHUTTERS
above cut represents a new and very ingenious device for testing the speed of
shutters. The machine was designed by Mr. Fred Schmid, of the C. P. Goerz
American Optical Company, and is in use at their
of the apparatus is as follows: The lighted tube, supported horizontally, is
placed inside the drum, the drum is then revolved at a given speed which is
ascertained by a striking bell mechanism (SB), giving one stroke for every
five revolutions of the drum and thus permitting an accurate determination of
the speed of rotation. The speeds, in practice, vary from three to eight
revolutions per second and as the drum revolves each perforation therein
appears in turn before the slot in the front board. To a spectator who is
watching the operation the slit appears as a continuous row of light-dots
blending finally into one line of light.
shutter to be tested is attached to a camera, placed in front of the apparatus,
focused on the slit, and with the drum revolving at a known speed and the
shutter set for a given speed, an exposure is made. The photographic image which
appears on the negative is a succession of dots of which the single white dot
appearing on the slit in the reproduction is an example. The single and double
dots appearing in the reproduction are openings in the front board above the
slit and facilitate the counting of the dots by marking groups of five and ten
in the negative.
making the exposure a special plate holder is used which permits of the same
plate being used for a complete test of all speeds of the shutter. This is
brought about by means of a device by which the plate is raised or lowered in
the plate holder.
length of exposure is figured out from the negative in the following manner:
Knowing the speeds at which the shutter was set and the time value of each
dot, derived from the speed of revolution of the drum, multiplying the value
per dot by the number of dots gives the actual length of exposure. If the value
of each dot is determined at 1/1000 of a second and the shutter was set for
1/100 of a second ten dots would indicate the exposure to be 1/100 and the
shutter to work accurately. However under same conditions should 20 dots appear
in the negative the actual exposure world be 1/50th of a second and show the
shutter working slower than marked.
important feature in regard to this device is that it is equally well adapted
for testing focal plane shutters as between the lens shutters. This is due to
the fact that the record is produced on a straight horizontal line and will thus
be correctly exposed by the slit in the focal plane shutter.
device was designed in order to insure the accuracy of the XL Sector shutter
manufactured by this company and it is by virtue of many tests made with this
apparatus that they make the claim for their shutter that "you can rely on
Back to Technical Pages