how to overexposure a film using the ISO setting. i have a EOS 300 and i guess i can change the ISO setting in 1/3 steps. suppose i want to overexpose a shot (or possibly the whole film) by 1 stop. will a ISO400 film set to 200 (i.e. half the actual ISO speed) overexpose the film by 1 stop or 2 stops.

also i don't understand properly what happens when you overexpose by, say, 1 stop or 2 stops.

thnx

-- sajeev (chack74@yahoo.co.in), February 04, 2002

Answers

If you put ISO 400 film in your camera and set manually to 200, the camera will overexpose by one stop - thinking it needs to provide more light to the film for proper exposure. It will do this by widening the aperture or slowing the shutter speed or both, depending on what program mode you are using. When you overexpose by one stop, you double the ammount of light that reaches the film. Two stops will quadrouple the light - four times the ammount of normal exposure. One stop underexposure cuts the light value in half, two stops under: 1/4. etc. You can also do this with exposure compensation on your camera instead of changing the ISO - the effect is the same.

-- Derrick Morin (dmorin@oasisol.com), February 04, 2002.