Content copyright ESN labs 2016


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YouTube Videos of the Phochron in action. Test a box camera in under two minutes!

Use the menu buttons to select the “curtain shutter test” . The light source will turn on and a twin bar graph will be displayed on the LCD screen.Each bar graph is showing the light seen by one of the two active sensors.

Move the light source left and right, or up and down until the two bar graphs are at about 30 to 50% and are close to the same height. It is not critical to get them exactly the same. If you have the light source too close, it may be hard to get equal light levels.

Now set the shutter back to it’s timed setting.  Press the start button on the tester. It will display “waiting for trigger” on the LCD.  Trip the shutter and the tester will capture the timing waveform and numerical data.  Repeat to capture a series of tests and get an average.

To view the results of all of the previous tests, press the menu button “Summ”. A summary of the last 16 tests will be shown.  Press it again to go back to the testing screen. Press the “retest” button to clear the screen and start the testing over.

Curtain Shutter testing described

Now use a couple of rubber bands to secure the sensor module to the back of the film plane opening. Center it as best as you can.  Set the camera to it’s “B” setting, wind the camera  and open the shutter, You may want to use a cable release to hold the shutter open.

First you must set the switch on the back of the sensor module to match the style of shutter you have. Most older SLRs that have cloth curtains are horizontal style. Newer SLRs generally have vertical style shutters.  You can usually tell by watching the curtain as you wind the shutter. You will see the curtains moving either vertically or horizontally. Set the switch to horizontal by moving the slide switch toward the wire. Set it to vertical by pushing the switch away from the cord.

Look inside the lens opening and verify that you can see all four sensor holes. The should not be at all covered up by the film opening. Adjust the sensor module slightly to get the sensor positioned just right.

Now place the included LED light source in front of the lens opening. Keep it close, but not touching the mirror.  Use books or playing cards to set the height of the sensor so it is centered in the lens opening. You must hold the light source still to ensure repeatable tests.  Note: Any light source will work. Any bright light will work. You can even use the flashlight in your cell phone.

Testing of 35mm SLR curtain type shutters is more involved than simple shutters. To fully evaluate the performance, the individual speed of the two curtains should be measured. Properly operating curtains will guarantee an even exposure across the film plane. Both vertical and horizontal curtains can be tested.

Interpreting the data:

There are two waveforms displayed. One is the light as seen at one edge of the film plane, and the other is the light seen at the other end of the curtain travel.  The tester is doing two simultaneous measurements. These are labeled Sensor 1 and Sensor 2.


The shutter speed measured at these two points are displayed. In a properly working shutter, these numbers will be very close.


Curtain time is the measure of the time it takes each of the curtains to cross the film plane. They are displayed as Curtain 1 and Curtain 2. These two numbers should be nearly the same. The difference in curtain travel times is displayed as a delta percentage.  A curtain speed difference greater than 15% can lead to uneven exposure.


Adjusting curtain speed is something that must be done by a qualified service technician. If your camera is working for you now, then there is no need to have it serviced.

Watch a Youtube video of curtain testing on an SLR. Click here