Exposure: A simple guide

[ricktas]

With all the features on your camera, there are really only three. When you use things like Scene modes, they are just preset variations of three camera settings that help ensure you get a good result. In Auto-Mode, you camera makes an evaluation and adjusts these same three settings. You might have a myriad of dials and menu options, which you can pick and choose, but these are often only simplifying the same three settings again!

What are these three camera settings that are the basis of all photography. They are the shutter speed (the time which your camera's shutter is open and your sensor, or film, is exposed to the light reaching it through the lens. The aperture, this is the diaphragm within the lens that can be closed or opened to differing sizes to control how much light hits the sensor, and the final one is ISO. ISO is the sensitivity of your sensor or film to light.

So using these three settings alone, you can basically achieve everything your camera does in auto, semi auto modes, and below is what each one does

Shutter Speed

The shutter speed controls how long the light coming through the lens apertures is allowed to hit your film/sensor. Slow shutter speeds can be minutes, seconds, or some of the lower fractions of seconds, like 1/2 a second, 1/4 of a second. Fast shutter speeds are usually very fast, like 1/1000th of a second. The faster the shutter speed, the more movement is frozen and the sharpness of moving objects will be increased. A guideline is that you can generally hand-hold your camera for a shutter speed that is the inverse of the focal length. So if you are shooting with a 200mm lens, then 1/200th of a second should allow you to hand hold your camera and get a sharp photo. Shooting at slower shutter speeds either requires a very steady hand or some sort of stabilising (a tripod). Slower shutter speeds allow blur (like moving water effect).


Aperture

Aperture lets you control the diaphragm in the lens, thus how much light hits the sensor/film for a given shutter speed. Apertures are fractions. So aperture f2.8 is larger (more open) than aperture f22. These are really 1/2.8th and 1/22nd. So 1/22nd is smaller than 1/2.8, thus an aperture of f22 is smaller than f2.8. An aperture of f2.8 is bigger, so will let more light hit the sensor/film for any given shutter speed than will f22. This is apparent for all aperture selections : f4 is smaller than f2.8, but bigger than f8. The more open you aperture, the less the depth of field : distance, front to back, in your photo that will be in focus, outside what you focus on.

So a photo taken at f2.8 will have a shallower area of your photo that is in focus compared to a photo taken at f22.

ISO

ISO is the camera's sensor (or film) sensitivity to light. Low ISO's like 100 and 200 are less sensitive to light than ISO 800 or 1600. Lower ISO means less noise or grain in your photo than higher ISO's. As you go higher and higher with an ISO, the more noise/grain is visible in your photos. As you increase the ISO to a larger number and make your sensor more sensitive to light, it means you can use a faster shutter speed.

USING ALL THREE

To get a great photo, you need to decide what your photo is going to look like, before you take it, and then adjust the above three settings to get the result you want. All three settings above are not independent, but they can be independently adjusted. Changing one without changing the others may not get you the photo you want.

Say you want to get a slow milky water effect, you need a slow shutter speed, but just adjusting the shutter speed and nothing else might result in your photo being over-exposed. So you set your camera to 1/2second shutter speed cause you want to show the blur of the water, but then you will likely need a smaller aperture (larger number) otherwise the amount of light hitting your sensor could be to much and you end up with pure white areas with no detail in your photo. So with 1/2 second shutter speed set, you can close down your aperture to say f22 to reduce the light through the aperture in the lens.

It is getting late into the afternoon and you are shooting kids sport. You are using a fast shutter speed to freeze the action, say 1/500th of a second, but as it gets darker, your photos are coming out dark. You can increase your ISO from 100 to 800 to increase the sensitivity of your sensor to light, thus getting shots that are not so dark.

See how all three settings work together to achieve the result you want/need. Learning how Shutter speed/Aperture/ISO inter-relate is the basis for all photography. So come to grips with how they work and interact with each other, and you are on the way to understanding your camera more fully and being able to make educated choices in relation to camera settings, to get the photo YOU WANT!