To most photographers, leaving home with a non-functioning or completely absent light meter is equivalent to shooting without a camera. All modern cameras come well-equipped with sensors that measure light in all sorts of ways: spot metering, centered metering, weighted metering, and the list goes on. New photography students are told to purchase a camera only if it comes with a fully-equipped functioning light meter, and turn the camera down if otherwise. What if one no longer needed it? Wait, wait, slow down. There is such a thing as the human brain, and those who took photographs back in the day never had the luxury of a meter telling them exactly what exposure to use. Logic dictates that there must have been another way these people accounted for the amount of light in a scene, so of course there is – there are simple rules for one to follow in order to achieve a proper exposure. Before a person understands this, however, he or she needs to understand the basic components of what creates a proper exposure.
Film speed is how fast the film darkens when exposed to light, measured in ASA or ISO numbers, standing for American Standards Association or International Standards Association respectively. Their values are exactly the same: a film speed of 100 in ASA is the same as a film speed of 100 in ISO, as is 200, 400, and so on. 200 darkens twice as fast as 100, 400 darkens twice as fast as 200 and four times as fast as 100. The film speed of 100 is suitable for heavy-light situations, generally outdoors while a speed of 400 is more suited towards low light situations, such as inside rooms with mediocre lighting. Anywhere in between and the film becomes somewhat more flexible as far shooting between any lighting conditions, but the acceptable range of shutter speeds and aperture combinations will decrease. Finally, film with a speed of 100 has finer grain than one of 400; hence it is generally better to use lower film speed if conditions work.
Shutter speed is quite simple to understand: it is how long the shutter remains open to expose the negative. On the camera, shutter speeds are generally denoted by whole numbers such as 1, 2, 4, 8, 15, 30, 60, 125, 250, etc. The actual shutter speeds are in reality the reciprocals of these numbers. The 8 indicates that the shutter will be open for 1/8 of a second, the 60 indicates 1/60, and so on. The two things that need to be taken in consideration for selecting a shutter speed are how much light is entering the camera and which objects are in motion within the soon-to-be photograph. Selecting a longer shutter speed for a moving subject will make it appear as if it is in motion, while a very fast shutter speed to essentially freezes the object in motion. Each successive shutter speed number designates either double or half of a difference in light entering the camera. Going from shutter speed 1/4 to 1/8 halves the amount of light. Going from 1/125 to 1/60 is doubling the amount of light as the shutter is open twice as long as before.
The aperture is the final mechanism of the camera affecting exposure; it is the “pupil” of the shutter that constricts or opens up to allow more or less light into a photograph. It’s width is represented in f/stop numbers, each consecutive increasing f/stop closing the aperture down to make it smaller thus letting in half the amount of light as the preceding one. 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22 are a few numbers used for aperture. The number is actually a representation of the ratio between the focal length of the lens, which is the distance from the negative plane, and the diameter of the aperture. The focal length divided by the f/stop number returns the diameter of the aperture at that particular f/stop. Depth-of-field is the range in which objects will appear sharp within a photograph. The more wide the aperture is, the less depth-of-field that will be in the image, and reversely the less wide it is, the more depth-of-field.
To recap, three fundamental things affect exposure in cameras: film speed, shutter speed, and aperture. Film speed is independent while shutter speed and aperture work together to obtain a proper exposure for a scene. The common “photographer” today with a lot of money so spend may purchase a camera for a large sum of money only to shoot it on automatic mode. The less common and more revered photographer actually ventures out of that into the manual exposure setting, in which he or she chooses the aperture and shutter speed combination based off what the light meter says to do. While it is true that by going into manual the person taking the photograph has much more control over what he or she wants to see her photo ending up as far as movement and depth-of-field are concerned, but he or she doesn’t have total control. Just as the camera thinks for the photographer when the average Joe snaps away in auto mode, the camera still thinks for the photographer regarding obtaining a proper exposure in the image. To reclaim one’s camera, one must be at one with the light meter. In fact, forget the light meter altogether – instead, become the light meter. No, really – it’s not that hard turning into it. Every person has two eyes and one brain that can detect much more information and process it much more deeply than some computer inside a camera.
Exposure value is a measurement of the amount of light within a scene. The numbers range from about 0 all the way to about 20; each increment doubling the amount of light in a picture. Light meters incorporate this form of this thinking, and so can a photographer. Exposure values are useful because they can tell a person exactly what aperture and shutter speed combinations are acceptable for a giving lighting situation and a given film speed; charts exist that describe a wide range of exposure values. For example, pretend that you’re working with an exposure value of 15 on film that has a speed of 100, and it tells you that for the given situation, a shutter speed of 250 and aperture of f/11 is acceptable. However, you just finished shooting that roll and the only one you have left is a roll of speed 200. Because film speed 200 darkens twice as fast as film speed 100, either the aperture will need to be closed down a step or the shutter speed will need to be halved thus the chart will tell you this. There are a lot of ways to play around with the information that exposure values and their charts give, thus allowing photographs to be taken without the aid of a light meter.
While it’s all nice and dandy not needing to rely on light meters, one must still rely upon a chart. Hence, the computer really hasn’t faded into the brain at this point – it has only traveled from inside the camera to a printed out sheet. The goal is to get it within the head of the photographer, and this is where the “sunny f/16 rule” comes into play. It states that to obtain a proper exposure, one should set his or her aperture to f/16 and proceed to set the shutter speed as close as possible to the reciprocal of the film speed. It combines everything about exposure values into one simple and easy-to-remember rule. Have a film speed of 100? Set the shutter speed to 125. Have a film speed of 400? Set the shutter speed to 500. The only catch is that this rule works only in the exposure value of 15 – that is, subjects in bright or slightly hazy sun. All one has to do is remember what constitutes an exposure value of 15 along with the few ones below it and he or she can adjust the camera accordingly. It is not even necessary to remember the numbers themselves; just remember when to double or halve the amount of light coming in depending on various situations. Light meters often lie, especially in naturally bright situations such as sand and snow – this rule has no problem with that. Just remember to start at f/16 and the shutter speed that is nearest to the reciprocal of the film speed. Double the amount of light entering the camera when the sky is patchy cloudy. Double it again for a slightly overcast sky. Double it again for a heavily overcast sky. Double it again if shooting in sunset or open shade. The process is quite simple: remember when to double or halve the light – no chart or light meter is ever needed. Memorize the most common situations and their positions relative to the exposure value of 15 and one is set to take photographs without carrying any information regarding to exposure; motion and depth-of-field can be adjusted accordingly by halving the shutter speed and closing the aperture a stop, and vice versa.
Pretty soon this process will come naturally, and then a person can literally throw away their light meter. Well, rather than tossing it in the garbage one could actually sell it to somebody that needs to use it, and make a few bucks off that other person who is unable to calculate the exposure inside their head. If a person really wants to keep their light meter for when they’re in tricky lighting conditions, that’s fine, they can still freak their photography friends out by predicting what their cameras’ light meters will read. The beauty of just know when to use what exposures based of lighting conditions the eye sees is profound: no guesswork is required to fix a light meter’s computerized thinking, the photographer is still able to retain control over his or her shutter speed and aperture, and the exposure turns out perfectly natural almost every time.
Link:
Exposure Value ChartLink:
Exposure Value Relationship Chart 
Reply
