Todd's Basics of Photography Page
Some of the following started out as a letter to my daughter, Sarah. I've edited it somewhat, but the odd inside joke may still be present.
Shutter Speeds and what they do:
The shutter speed is kind of the stopwatch of the camera. It sets how long the camera stays open. On most cameras, all the shutter speed numbers indicate fractions of a second; that is, the setting "500" means the camera will stay open for 1/500th of a second. Commonly available shutter speeds are 1000, 500, 250, 125, 60, 30, 15, 8, 4, 2, 1 and "B" (more on B later). Note that each speed is half or twice as much as the speed next to it. 1000 lets in the least amount of light (camera is open for a very short time) and is called a "fast" speed, while 1 lets in the most amount of light (camera is open for a relatively long time) and is called a "slow" speed.
What shutter speed you choose can have a big impact on your photos. If youíre taking pictures of things that move, you can decide to "freeze the action" and shoot at 1000. This will stop all but the very fastest motion (wonít stop an airplane propeller, but it will stop a baseball). On the other hand, some things that move donít look right when theyíre stopped. Most of the pictures Iíve taken where moving water is the subject have been taken at slower speeds to show blurry motion. Experience and practice will help you decide what youíre trying to do, and which shutter speed you should use. When in doubt, try the same photo a few different ways. Taking notes helps you learn, too.
With a little practice, youíll find you can shoot hand-held at 60 (1/60th of a second) and still get a sharp photo, but youíre starting to run into camera shake at about that speed. With guns and cameras, you want to "squeeze the trigger, donít jerk it". At 60 or slower, if you donít have a smooth motion on the shutter release, the jerking motion youíre putting on the camera will show up as unsharp photos. Sometimes itís very subtle, and you just think the camera isnít very sharp. At slower speeds, bracing the camera is a big help. You can use a tripod, or you can rest the camera on anything stable thatís at hand. Iíve used fenceposts, the hood or roof of a car, walls, whatever. When we were in Washington, D.C., I used a little tiny tripod a few times and braced the tripod against the wall.
The "B" setting is special. It stands for "Bulb", and the camera will stay open as long as you hold the shutter button down (hours, if you like). I donít know if "Bulb" refers to the old flashbulbs where the camera was opened, the flash was fired manually, and the camera was closed; or if it refers to the bulb-like squeeze thing that some cable releases use. "B" is almost always used with a tripod to hold the camera still, and a cable release with a lock to trigger the shutter and lock it down. If youíve ever seen photos where car lights are "streaking" through the photo, they were made with long exposures (say 30 whole seconds or more) typically done on the "B" setting. Another thing you can do with "B" is star trails. You can leave a camera open on a dark night for an hour or so, and the earthís rotation will cause the stars to paint curves across the sky (the center of the curves is the North Star in the Northern Hemisphere).
Apertures and what they do:
The aperture is like the pupil in your eye. Itís a mechanical "iris" inside of the lens that opens and closes to varying degrees to control the amount of light that passes through the lens. When an aperture is "wide open", itís gathering all the light the lens is capable of. When the aperture is "stopped down", or closed down to a pin-hole, itís letting pass the smallest amount of light possible. This is just like your eye: in a dark room, your pupil opens wide to gather light; in bright daylight, your pupil closes down to cut back on the amount of light entering your eye.
Apertures are expressed in ratios; the ratio refers to the focal length of the lens over the effective optical diameter of the lens. Itís this part of the definition where the aperture picks up its other name "F-Stop". Iím guessing the "f" stands for "focal", but Iím not sure. In photography, "aperture" and "f-stop" are pretty much interchangeable terms. An aperture might be expressed as "1:2.8" in deference to this ratio definition, but itís more commonly called "2.8" or "f2.8".
The available apertures of the lens on a typical camera are: 2.8, 4, 5.6, 8, 11, 16 and 22. You might notice that every other number is double / half the next. (that is, 11 is roughly twice 5.6). Each aperture or f-stop lets in half as much or twice as much light as the adjacent one. The reason the numbers are so odd (as compared to the shutter speed scale) is that these ratios are expressions of circular area (think of that iris / pupil thing). Since circular area is determined by the formula of Pi * Radius Squared, you get twice the area by increasing the diameter by a factor of the square root of 2 (if you havenít had geometry in school yet, ask your mother to explain it).
The maximum aperture on many cameras is 2.8. This setting lets in the most light, and is sometimes called "wide open" or the "fastest aperture". The minimum aperture is 22. This lets in the least light, and is called "stopping down" or the "slowest aperture".
In addition to controlling the amount of light that passes through the lens, the aperture controls something called "depth of field". In technical terms, depth of field is the expansion of the plane of focus into a zone of "acceptable sharpness". A wide open aperture like 2.8 has very narrow depth of field, while a "slow" aperture like 22 has very broad depth of field.
If youíre taking a portrait of someone where the personís face pretty much fills the frame, typically you focus on the eyes. If you choose a narrow depth of field by using 2.8, the ears will be out of focus, and if the depth of field is particularly small, the tip of the nose will be out of focus. This can be a nice effect, particularly if the background has distracting stuff in it.
If youíre taking a landscape picture where thereís a field of flowers in the foreground and a mountain scene in the background, you might want a very broad depth of field such as 22 so that the foreground flowers and background mountains are all in focus.
Film Speed (or ASA or ISO):
Film speed is a rating of a filmís sensitivity to light. A film with an ASA of 800 is very sensitive to light, while a film with an ASA of 25 is not very sensitive to light. Film speed is generally inversely proportional to image quality. You might need a high speed film like 800 ASA to shoot basketball indoors without a flash, but the resulting pictures might be grainy (like a newspaper photo) and the color is not the best. If you shoot an ASA 25 film, youíll find that you have to have full daylight to take a picture, but the resulting images have very good color and very little grain. These are generalizations, your actual mileage may vary.
Some other generalizations: Slide film has more contrast than print film. Print film has more exposure latitude than slide film (exposure latitude is another way of saying you can screw up the exposure, miss the correct exposure and still get an acceptable print).
Every time you double the film speed, itís like adding one f-stop or one shutter speed to your exposure. Which leads us intoÖÖÖÖ.
Putting it all together in exposure (shutter speed + aperture + film speed).
The "correct" exposure for a given scene is a function of at least 3 things: shutter speed, aperture and film speed. For a given scene (and by "given" Iím implying the light is not changing like the sun moving behind a cloud) there are multiple combinations of elements that will yield a correct exposure. For example, with 25 ASA film, the daylight (full sun) exposure can be expressed as follows:
Where any one of the Aperture / Shutter Speed pairs will cause the film to be exposed by the same amount. Do you chose large depth of field at f16 and use the slow shutter speed of 30? Or do you prefer to use the action stopping shutter speed of 500 and the narrow depth of field of f4? These are the choices you make in photography.
If you move from 25 ASA film in the previous example to 50 ASA film in this example, you see that the exposure (same setup, daylight) has shifted "one stop". One stop refers to a change of one aperture, one shutter speed or doubling / halving the film speed.
Jumping up to 400 ASA film, still in daylight, yields the following:
By the way, all of these are based on a rule of thumb called the "Sunny 16 Rule". This rule states that the correct exposure for a film in sunny daylight is aperture of f16 with the shutter speed equal to the ASA (pick the nearest one).
Lastly, in some respects, exposure is a matter of opinion or what youíre trying to "say" with the photo. You might be trying to draw the eye to some details in the shadows, so youíre exposing for that. Or you might be trying to make the shadows dark and mysterious, so you change the exposure again.
Exposure oddities and 18% gray
All exposure meters are basically stupid. Theyíre calibrated against some standard, and if youíre photos arenít standard, then they might tell you the wrong exposure. The standard that meters are set for is called 18% gray. 18% is a measure of reflectance. Meters donít care about color, just how bright a tone of gray is. In most cases, this works out fine. You can actually buy a piece of cardboard in a camera shop that is 18% gray (commonly called a "Gray Card" of all things) to use as a reference. Green grass reads as roughly 18% gray. Arizona desert sand and scrub is probably about 18% gray. Itís the extremes where you get into trouble.
Letís say you want to photograph a snow scene. If you point the camera at it and take a meter reading, the camera will assume itís gazing upon an 18% gray scene and expose accordingly. Well, itís not gray, itís white. The cameraís chosen exposure will render the snow as gray, however. The opposite is true for the proverbial black cat in a coal bin. The camera meter does not "know" itís pointed at a black subject, and it will pick an exposure to render the scene as gray.
The classic example is the white wedding dress and the black tuxedo. Thereís a reason why wedding photographers are well-paid, and itís not entirely about dealing with the stressed-out mother-of-the-bride. Itís very tricky to get the exposure right on either all black or all white subjects.
Cleaning Lenses and Filters
Lenses and filters are different from window glass. They usually have coatings that make them better for taking pictures. You can see the coatings if you look for the reflection in the lens. If the reflection has a color cast to it, like purple or orange or green, the lens is coated. You canít use "Windex" or other commercial glass cleaners on a coated lens, it will damage the coatings. Generally, use no liquids. Use a high quality lens paper made for cameras (not those eyeglass papers, either, they contain anti-fog silicone which can damage the coatings). If you need a little moisture to lift a fingerprint or something, breathe on the lens and then wipe with the lens paper. Itís better to breathe on the lens holding it above you. Itís easier to spit on the lens then you might imagine, and one "loogy" can ruin your whole day. If you need more moisture than breath can provide, use a photographic lens cleaning fluid like the one made by Kodak. Put a small drop on the lens paper, and then wipe the lens to remove the offending fingerprint or what have you. Never put lens cleaning fluid directly on the lens; it can seep down inside and really screw things up.
What makes a good photograph? Thereís a couple of rules for composition (and of course most rules get broken occasionally). First rule: donít "bulls-eye" your subjectís face. Since you have to focus using the center of the viewfinder, and of course you want the face to be in focus, itís tempting to focus there and then go ahead and take the picture with the personís face still in the exact center. That usually means youíre leaving a large portion of the frame empty above the personís head. Another way to say this rule is fill the frame. Always look at the whole frame and make sure youíre doing something interesting with it. Sometimes moving closer to your subject is whatís needed.
Another rule that gets a lot of use is the rule of thirds. If you think of a tic-tac-toe board overlaying the frame, the intersections are where you should place things of interest. Itís called the rule of thirds because the frame is divided in thirds horizontally and thirds vertically. I think Leonardo DaVinci came up with this one first. If youíre taking scenic pictures, you usually donít want to put the horizon through the center of the frame. Place the horizon along one of the "third" lines. An exception can be when doing mirror image reflections in a body of water; then you might do one with the horizon centered, and then try moving it around. Some of the strongest images Iíve seen of water reflections have either no horizon, or very little showing above the water.
Be aware of leading lines and where they take the viewers eye in a photo. Railroad tracks disappearing in the distance (vanishing point) are an example of leading lines. Sometimes the leading lines are the subject of the photo. Other times, they unintentionally lead the viewers eye away from the main subject.
Watch out for distracting backgrounds. Itís easy to forget about this when youíre taking the picture, but then when you get it processed and you see the telephone pole growing out of someoneís head, you realize youíve made a mistake. Along those lines, the eye goes to whatís brightest and sharpest in the photo. Having a bright background is usually distracting.
When shooting scenic pictures, think about some foreground interest. Too often, we become fixated on looking at whatís "out there" and the resulting photos arenít as good as they can be. You can include a natural frame in your photo by including trees or branches at the edges or along the top. Sometimes you can lower your shooting position to include grass or brush in the foreground. Long grass in particular doesnít even have to be in focus to add interest in the foreground.
I've added a new page of sports photos here:Special Olympics of Washington photos of Summer Games
Ron Hashiro has a few pages on photography basics here.
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