ACL light-meter calibration

ACL built-in light-meter calibration by Erkan Umut

The ACL meter works based on the calibration to any meter principle. It is not a regular built-in camera meter seen in most cameras. So you cannot find an ASA (ISO) index. But the meter is coupled to the frame frequencies (speeds). You need an external meter with the reflected light reading capability or a spotmeter, a Grey Card (having 18% reflectance), and two lights for the 45˚ homogeneous lighting.

1. Just adjust the handheld meter with the film speed (ASA/ISO/DIN) you are going to use and the exposure time (@24fps, if it has CINE scale; if not, T (Time) 1/49 exact so close to 1/60 towards 1/30).

2. Light the gray card with your lights (left and right, each one at 45 degree) and be sure to light evenly. Put something on the middle of card like a ruler, see the shadows, and be sure that shadows are the same. If not, relocate your lights until it’s done.

3. Locate your handheld meter close by the card if its not a spotmeter towards it. Take a reading. Be sure not to create shadows by your body on the card! (For the reflected reading method refer to the meter’s manual.)

4. Take your ACL camera, maintain a steady ground or better use a tripod, and frame the card fully. Do not forget to set the camera film frequency @ 24fps, too.

5. Set the F/stop number (that you’ve read on the handheld meter) on the camera lens iris.

6. Rotate the camera’s meter potentiometer knob until the lights in the viewfinder give the proper exposure (see the ACL manuals).

That’s all. Your camera meter is calibrated now, and will act like a calibrated built-in camera spotmeter. Good luck to everyone!