|Favorite Classics Camera & Repair Articles Test Equipment EV Tester|
This is a very handy tester in that it tests the combination of shutter speeds and apertures. In other words, itll tell you if the exposure is correct. Cameras can be checked in either manual or automatic.
|Build the unit as per the photos and schematic. Remove the meter bezel
and make a facplate with "0" in the center of the needles range.
"+1" will be located where one stop over exposure would be and
"-1" in the one stop under position. Only these three numbers
need be on the face. But intermediate marks for half stops and quarter (or
third) stops can be added. Note that the "+1" and "1"
will be a two to one ratio from "0". This is because light quantity
is doubled between stops. Use a calibrated Adjustable
Light Source and a good metering electronic camera to calibrate the
EV tester. I used a combination of all three of my Canon EOS cameras.
The tester will only be accurate over a narrow range of EVs. This range will depend upon components used and light source.
Reset button must be pushed between exposures.
Calibrate by setting the good metering camera to ASA 100 and aperture priority. Set the Adjustable Light Source to the highest EV it is capable of. With camera a standard distance from light and tester held at focal plane, release shutter. Needle should go to "0" in the middle of the meter. If it doesnt, adjust the trim pot closest to the battery until it does point to "0". Release shutter at various aperture/shutter combos but still at same EV. If the needle steadily wanders in one direction as camera settings increase/decrease adjust the other trim pot until the needle no longer wanders. Readjustment of the first trim pot will be necessary to bring needle back to "0". Check at several EVs.
To test an unknown camera, set the Adjustable Light Source to EV wanted and camera to ASA 100. Look on EV Chart and set shutter speed and aperture to any combo shown for the set EV. Open the cameras back and position the tester so no light leaks through the seal. Turn tester on and push reset button. Make exposure. Needle will jump to exposure level. If needle points to "0" exposure is perfect. Do not expect old mechanical shutters to be very accurrate. +/- .25 stop is VERY good. Even new electronic shutters vary by +/- .1 stop or more.