Exposure Compensation Follow-up

[raj_gj]

I have been reading the previous posts on exposure control and

compensation. This is what I understand... first I put my camera in

aperture priority mode and decide the depth of field, then take the

meter reading, then based on that I either choose the exposure

compensation or go in manual mode and reduce the shutter speed by

half for 1 step over exposure or double it for -1EV.

 

Comments??

 

Raj

[jim_strutz]

Sounds like you got it right.

[nevilleb]

Raj,

 

You need to go out there and shoot, shoot and shoot till you get the relationship between shutterspeed, aperture and depth of field like the back of your hand.

 

Essentially, depth of field will be an issue depending on - well, how much of dept of field you want. Shutter speed will be an issue if you wish to capture fast moving (or slow moving ) objects. Yet, twiddling with one affects the other.

 

The faster the shutter speed, the wider the aperture. The wider the aperture, the smaller the DOF. The slower the shutter speed, the narrower the aperture. The narrower the aperture, the greater the DOF.

 

Exposure compensation is essentially nothing but getting the camera to either automatically (or manually) over or underexpose.

 

Let us say you are shooting a tightly cropped portrait of a man on a brightly lit day using say ISO 100 film. Let's say you are using a 100mm lens. 100mm will reduce DOF, and lets say you decide to go with an aperture setting of f8.

 

According to the sunny f16 rule, the "correct exposure" for the subject would be 1/125th of a second at f16. In this case f8 is two stops wider than f16, so you would need to expose at 1/30th of a second.

 

All this will be handled by your meter automatically, assuming that the subject is a neutral tone. However, let us assume that there is a white-washed wall in the background of the subject. Your camera's meter may read a large occurance of the wall to be the subject itself and be fooled.

 

Essentially the meter will try to reduce the white wall to greay - essentially underexposing the image by around two stops. In our case, the meter will read around 1/7th of a second or so at f8 instead of 13oth of a second at f8.

 

We overcome the problem by exposure compensation. Either go to manual mode and set f8, t=30, or dial in exposure compensation of two stops overexposure on the camera itself in AV mode.

 

Get the picture? No pun intended.

 

Neville Bulsara

[raj_gj]

Thank you for your responses.

 

Raj