[Benji]

Here is how I calibrated my hand held meter so when I set it at ISO 100 my camera's sensor will record the image properly at ISO 100. I got an 18% grey card and placed it on a chair facing the light (a flash unit.) For calibrating a meter used for ambient light you do the same. I set the camera on manual and I also both the hand held meter AND the camera to ISO 100 and took an accurate meter reading at the card. I set the shutter speed at 100 (In flash photography the shutter speed is inconsequential unless there is lots of ambient light) then I set the aperture at whatever the hand held meter reading was. I made an exposure of the card ONLY. Fill the frame so only the card is in the image. You may need to "fool" the autofocus or disable it. I made my first of several notations of the aperture. Then I made four more exposures, two in 1/3rd increments more and two at 1/3rd increments less than the original reading making notations as to the number of the image and the aperture reading used for that image. NOTHING else was changed. I then loaded the images into my computer and Photoshop. In Photoshop I went to "Window" and in the drop down menu I clicked on "Histogram." When you bring up each image there will be only one spike. The image that has the spike dead center is the only image that was correctly exposed. Note which image it was and confer with your notes. If it was the very first image your hand held meter is set perfectly. If it was one of the other four images you must do one of two things. If your meter has a small dial (usually inside the battery compartment) you can take a tiny screwdriver and rotate the screw a little to adjust the meter to match the correct reading. This will allow the LCD reading on the face of the meter to read ISO 100. If your meter does not have that dial you will need to increase or decrease the ISO either 1/3rd or 2/3rds (+ or -) to get the correct reading. The ISO on the face of your hand held meter will now read 80, 64, or 125, 160, but the camera will stay at ISO 100. If you have a second meter that you use outdoors you will need to calibrate it the same way.

Benji