Welcome aboard photo enthusiasts. I have mentioned photography means “painting with light,” and over the course of the last year discussed many ways you can control light with your compact camera its shutter, aperture and flash. The most efficient application of these controls is determined by your knowledgeable brain when using Av, Tv, or M, that is Modes that allow your decisive input.
When you use any automated Mode, such a “P” on your camera, then you are relying on the electronic brain built into your camera, which you may surmise is not as discerning as your own. It will make decisions that do not necessarily achieve the results you desire. The problems that can occur often stem from how the camera reads light.
The first step to taking any photograph with any camera in any Mode is reading the light or brightness of any scene or subject. All measurements are based on 18% grey. There are two general light reading methods, one being an incident reading and the other a reflective light reading.
Professional photographers often use a hand held light meter (independent from the camera) to make incident readings. That means measuring the amount of light falling on to a subject. It allows for precise measurements around the subject in the highlights and shadows for a more accurate exposure settings.
Light meters built into all cameras, including our compact cameras, read reflective light or light reflecting off a subject. Turning the camera on automatically turns the meter on. If in a Manual Mode you can adjust the proper exposure (via Aperture and Shutter settings based on the light reading), and in any Auto Mode the camera will adjust the proper settings.
Are the exposures always set properly by the camera in Auto Mode? In short ….no, and here is the why. Just about every meter in camera takes an overall light reading, which covers the entire frame. The “frame” is the rectangular area you viewing either through your viewfinder or on your LCD screen to photograph.
Camera Manufacturers set light meters to take an overall reading with more emphasis to read the center and bottom of the frame (see diagram), knowing that most subjects will be photographed in center frame or the most important part of a pictured landscape is what is at the lower half of the frame (not the sky). Most of the time this works well, but not in every case.
Light meter readings often go wrong when taking a full length subject against a predominantly bright or dark background. For landlubbers the best example is a subject against a snow white background. The camera meter tells the camera brain “it’s so bright, there’s so much light” so stop down the shutter and/or aperture. The result being your subject is significantly under-exposed and the snow is not white, but 18% grey. For seafarers the predominantly dark ocean background will have the opposite effect. The camera meter tells the camera brain “it’s dark out, open up the aperture and/or shutter,” with the result of over-exposing your subject and background.
[This leads to an important aside – in digital photography it is better to err on the side of over-exposure (as opposed to film photography were the opposite, exposing for the shadows, holds true).]
There are several solutions to getting a proper exposure in situations where the camera meter is fooled by a scene to take an erroneous reading. The quickest easiest best solution is to check your manual to see if your camera light meter (like my compact) has a spot meter mode. When set to spot meter it measures a narrow area in the center frame.
Another way that is accurate, but not very practical is to get very close to the subject to take a reading, being careful not to stand between the light source(s) and subject.
Knowing that proper readings are based on 18% grey, another method I’ve used is to aim at something (under the same lighting conditions) that is equivalent to that shade of 18% grey, like green grass.
You can only see the result of a reading by a +/- (0ver/Under) numerical value (on my LCD in the upper left corner) when you set the Mode to Manual. And only in this M Mode can you make adjustments for the proper readings by changing the shutter and/or aperture until you have a value of “0” that will result in the right exposure settings.
Let me summarize the principle objectives of this article. Every camera has a built in reflective light meter based on an 18% grey standard. It measures (reads) light reflecting off a subject. Readings are taken in an overall pattern with extra emphasis towards the center and bottom. Spot readings of 5 to 10 degrees in center frame are also available in many compact cameras. There are situations were a meter can be fooled to make the wrong exposure. If you can recognize those situations you can make aperture-shutter adjustments using the M (manual) Mode. With that said, permission to come ashore.
The quickest, easiest, best solution to getting a proper exposure in situations where the camera meter is fooled by a scene is to check your manual to see if your camera light meter has a spot meter mode. When set to spot meter, the camera measures a narrow area in the center frame.