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Photography help: What is aperture, shutter speed and focal length?

What is Shutter speed?
- do lower settings = brighter pictures

Apeture: the opening within the lens. The word literally means “hole.” The smaller the number, the larger the hole – and the shorter the depth of field (that which appears in focus.) If you are doing a portrait and want only the person in focus, use a small number like 2.8 ; if you want everything in focus use a large number like 22. These relate to focal length, see below. Each number in sequence indicates a doubling/halving of the amount of light between it and the next number: 2.8 lets in TWICE as much light as 4, which lets in twice as much as 5.6, et cetera. (I emphasize twice as Fraud has it wrong: nothing is 3x in photography. It is either double, or if you back the other way, ƒ4 lets in 1/2 the light of ƒ2.8).

Shutter speed: the amount of time the shutter is open allowing light to pass through the lens and hit the film plane (or sensor.) The numbers expressed are fractions: the larger the number the less time the shutter is open. A very short shutter speed is 4000 – you can freeze motion at 1/250 and the shorter the duration the shutter is open the sharper the frozen image will be. If you wish to blur motion, use a slower speed (smaller number). A flash syncs in many new cameras at 1/250, and with older ones at 1/125 or 1/60 (expressed 250, 125 and 60 respectively.) You can use your flash at that speed OR SLOWER. So you can have a frozen subject in a blurred background. Notice these numbers are roughly doubles of the next, the shutter works like the aperture: each change of one stop indicates a doubling (or halving) of the time the shutter is open. You can use any shutter speed you need to give you the desired effect: you must adjust your aperture (and ISO) to match the desired shutter speed.

ISO: does mean International Standard, but works like shutter speed and aperture. ISO 100 film is only two stops slower than ISO 400. The scale is thus:

100 200 400 800 1600 3200 6400

Notice each is a double of the previous. This means it takes half as much light hitting the film/sensor to give an equivalent exposure. (Not three times!) It does indicate the film/sensor’s sensitivity to light. Grain and noise increase as ISO increases.

These three elements work together to produce a proper exposure.
If you want to isolate a subject (the portrait mentioned above) set the ISO to the lowest setting (if using film use slow film like 100). (I am assuming you are using the camera meter.) Focus on the face and be sure the meter is set for the center of the frame. Push the shutter button 1/2 way down, and look at the reading. Adjust the aperture setting until you get ƒ2.8, then look at what the meter says you need for a shutter speed. Set the shutter according to what the meter says.

NEVER POINT THE METER AT THE SUN. You meter the subject, not the sun. If you are using a hand held meter, put the dome on and take incident readings. You measure the light falling on the subject by placing it in front of the person/thing and pointing it at the CAMERA, not the sun.

Focal distance is the length between the film plane and the subject being photographed. You might want to measure for macro work or scientific work, and cinematographers measure for perfect focus, but hey most photographers just use the lens (auto or manual.)

Hyperfocal distance is the distance between the minimum focal distance of any given lens and infinity which appears in acceptable focus. It increases as the aperture value increases. So, at a small aperture, say 2.8 you have very little depth of field, at 22 you have a lot (ie everything appears to be in focus.)

Focal length is the distance between the rear nodal point of the lens and the film (sensor) plane. The aperture values indicate the number of times the hole can fit in that distance. So you see the higher the number the smaller the hole. (There’s a lot more reasons for this, this explaination is highly simplified but it will do for now.) The point of focal length is really more perspective: what do you see at 20mm vs 300?
In 35mm film photography 50mm is considered a “normal” perspective- the lens sees what you see, as you see it. A 20 mm lens is considered a wide angle, and a 300 is considered telephoto. The Angle of View (how much of a scene does a lens see on a 180º field) is the more important issue. The smaller the number, the larger the angle of view. Again, simplified, but sufficient.

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