Using The Light Meter/Exposure Calculator (A2B and A2F)
I. First, you must set the Tabs to the proper film speed.
Determining Film Speed: To set the Film Speed Tab, you must translate the film speed on the film cartridge, which is in ISO(ASA), to the film speed written on the camera, which is in Weston. Weston ratings are about 80% of ISO ratings; use the chart below to approximate your Weston rating. (If you are using film faster than 100 ISO, set the Film Speed Tab to 100 ISO/72 Weston and you will compensate for it in Step V.)
ISO | Weston |
15 | 12 |
25 | 20 |
50 | 40 |
100 | 72 |
Table
The Aperture Tab sits on top of the Film Speed Tab, but the two are not permanently attached. Slide the Aperture Tab down onto the Film Speed Tab until your Weston rating is the largest number exposed on the Film Speed Tab. Make sure that this setting does not get changed.
II.Move the Tabs together on the Slide so that the arrow on the bottom of the Film Speed Tab (stamped on top of the number 12) is lined up with the current lighting conditions. Your options are BRIGHT, AVERAGE, CLOUDY, or LIGHT INT (used for lit interiors).
III.Hold the camera with your elbows bent at a 90 degree angle and look through the Extinction Meter. Move the Slide until the Brightness Pointer lines up with the dimmest rectangular window you can see. If you are uncertain of which is dimmest, choose the brighter one.
IV. All of the calculations on the Extinction Meter are now complete. Look at the Shutter Speed Plate number to the left of the Aperture Tab to see which shutter speed should accompany which
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