With the introduction of the 8008S and continued on with the N90S and other models, Nikon provided a new exposure control called EV Compensation. Although a simple and very useful tool, EV exposure compensation, seems to be confusing for many photographers. Here is how and why I use EV compensation.

So what does EV compensation do? Answer, it recalibrates the cameras light meter to automatically over or underexpose by a fixed amount. The amount of over or under exposure is selected from a display scale that ranges from plus or minus 5 f-stops in 1/3 f-stop increments. Once set, the selected amount of exposure compensation will be applied to every exposure and/or meter reading made with the camera. You must reset EV compensation to zero to cancel it.

Here's a simple way to understand EV exposure compensation. Lets say all you have is a poor old manual camera with only a simple built in light meter. Could you still do EV compensation? Answer, yes! If you wanted say +1 EV or one f-stop of overexposure, you would simply zero the light meter then open the lens up to the next larger aperture. For example, if the meter read zero at F8.0, you would open the lens one stop to F5.6. You could also leave the aperture set at F8.0 and select the next slower shutter speed to overexpose by one stop, +1 EV.

Still using your poor old manual camera, you could even go one better and "automatically" do EV compensation. You would do this by adjusting the film speed, ASA, setting. Lets say you are using a 100asa film and as in the above example, want +1 EV or one f-stop of overexposure.

So why would you want to overexpose every frame on a roll of film? One answer is to correct for your films true speed rather than its rated speed, ie the speed printed on the film canister. Most films, especially E6 slide films, are not exactly the rated speed printed on the canister. Most slide films are 1/3 to 1 stop slower than rated. How can you tell? When you start shooting with a new brand of film, take some test rolls with your camera set at the rated ASA and no compensation. If the results are consistently a little dark, under exposed, then the films true ASA is slower than the rated value. If consistently a little over exposed, then the films true ASA is faster than the rated value. To correct for this simply use EV compensation or ASA setting to correct for this over or under exposure. You should only need plus or minus 1/3 to a maximum of 1 f-stop correction to adjust for a films true speed.

By the way, the poor old manual camera is the Nikonos-V. Also, on the Nikonos-V, each dot between whole values on the ASA scale are increments of 1/3 of an f-stop. Each tick mark on the light meter scale and EV scale, on the 8008S and N90S, also represent 1/3 of an f-stop.

Another use of exposure compensation is for setting the camera to properly expose a roll of film which will be Push Processed. I will cover "Pushing" next month.

Your questions and comments are welcomed.

Randy Morse
E-Mail: RMorse@rickeng.com