At a recent WPHS monthly meeting Paul Garrett handed me an instrument that looked a lot like an old analog electrical test meter but it was clearly marked "Mark XII Shutter Calibrator". This instrument was made in Japan and marketed by the Verselector Co. of Van Nuys, CA. My Internet research on this device came up empty. My guess is that it was made in the late 60's or early 70's before digital circuits became cost effective.

.

There is a fixed photocell located in the upper end of the unit. A remote sensing photocell with plug-in leads is supplied to allow for use in tight spaces. The thumb wheel control on the left side is used to set zero on the meter.

In operation the photocell acts as a switch when exposed to light by operation of the shutter. This causes a capacitor to charge up to a voltage that represents the time of exposure (Note 1). The measured voltage is represented on the meter by a scale that indicates the accuracy of the shutter speed. There are scales on the meter that indicate film speed or f-stop corrections that can be used in conjunction with an out of tolerance shutter. The standard tolerances for shutter speed variation are clearly marked by red and green bands on the meter. The Verselector is uncomplicated and simple to use.

I normally use a digital shutter tester and take 5 readings at each speed so as to be able to determine average shutter speed and standard deviation. This helps in analyzing any shutter problems. But the Verselector is so handy that it will certainly see more use in the future.

I have cobbled up a set of instructions for using of the Verselector and they are posted on my web site www.robertsuomala.com (see below).

Notes:
1. If you really want to get technical regarding the theory of R-C timing circuits I recommend checking out
http://www.northcountryradio.com/PDFs/column008.pdf

Battery: NEDA 220, 15 VDC.
Available from Battery Bob for $5.99 including shipping.
( batteryBob.com )
To install, remove back cover.

1. Place a bright light in front of the camera lens (see Note 1).

2. With the camera lens focused at infinity and the aperture wide open, locate the built in photocell at the film plane and approximately centered in the image frame.

3. Move range switch to desired shutter speed.

4. Set the meter indication to zero using the adjusting wheel located on the upper left side of the instrument.

5. Hold down the READ button and fire the shutter

6. Release the READ button and note the shutter speed error.

7. Press the RESET button and hold down until the meter indicates zero before making additional readings.

8. ALWAYS return the range switch to OFF when finished.

Cover the built in photocell to prevent stray light from falling on it.
Plug in the remote photocell. Red is Plus (+) and Black is Minus (-).
Proceed using steps 1 through 8 above.


Note 1: If light is not bright enough the readings will be erratic.


R. A. Suomala 10/17/08
rsuomala@earthlink.net