Accessory Shoe — see Shoe.
Aperture — the window through which light passes to expose film. The aperture is typically a circle (or as nearly circular as can be reasonably attained) that's set either very close to or within the lens. On most cameras the aperture can be continuously adjusted to vary the size of the circle. On older (or very inexpensive) cameras, a single aperture hole is drilled in a piece of material, and to change apertures, another pre-drilled aperture has to be moved into place. Non-adjustable holes are typically called Waterhouse Stops.
The aperture on the camera is one of two methods of regulating the amount of light that enters the camera and ultimately exposes the film or digital sensor (the other method is the shutter). The aperture-size directly influences depth-of-field and lens performance (resolution and contrast).
Aperture Priority see Automatic Exposure
Automatic exposure has been around in one form or another for a long time, but it really required on-board electronics to do it properly. This began showing up in the 1960s and bloomed in the 1970s.
Auto exposure evolved through a series of steps. The earliest cameras with built-in meters were uncoupled, meaning they worked independently of the rest of the camera. Coupled meters could adjust the lens or shutter. By the early 70s most of the better cameras had "match-needle" metering, which meant two needles were visible in the viewfinder. One needle was connected to the shutter and the other to the aperture, and by changing the settings, the needles could be brought together for what the camera thought was the proper exposure.
From there it wasn't a big step to let the camera have control of one needle and let it match the one the photographer set. This was called priority mode. A camera with shutter priority meant that the photographer set the shutter speed and the camera would set the aperture to the "proper" exposure. Aperture priority cameras had the photographer set the aperture and the camera set the shutter. A lot of the cameras in the 70s had these modes. A few of the top cameras like the Canon A-1 offered both.
With a little more computing power, the camera could be allowed to pick both. Camera makers began programing the cameras to make reasonable decisions on how to set both shutter and aperture depending on the amount of light it saw. f/stop and speed combination tables allowed the camera to look at a light level and pick a compromise between speed and f/stop that would give decent exposure. Canon called it program mode; other companies came up with their own names for the same thing.
Early cameras with program modes (like the Canon A-1 and Canon AE-1 Program) could only look at one compromise table, regardless of any extenuating circumstances. Later cameras like my Canon T70 have several, so you can tell it to favor a higher shutter speed or a smaller aperture, while still allowing the camera to run in full automatic mode.
Bayonet Mount — an extremely common method of attaching a lens to a camera body; mostly found on 35mm and medium format cameras that use interchangable lenses. Bayonet lenses get their name from the push-and-twist action that locks the lens into place. Bayonet mounts gained in popularity in the 1960s and left its rival screw mount sisters in the dust. Bayonet mounts weren't subject to cross-threading, could be attached and removed more rapidly, placed pins and electrical contacts in precise location every time, and locked into place securely.
Contrast — the quality that visually distinguishes two objects relative to each other. A simple example is to imagine two gray objects that are next to each other, with one partially blocking the view of the other. If the two objects are exactly the same color, it may be difficult or impossible to distinguish the true shapes of the object—they visually merge together.
Contrast comes many places in photography, but it's particularly import in lens optics. Good contrast, along with resolution, contribute to the apparent sharpness of the image. Good contrast is typical in dramatic images, and helps lend a dynamic, crisp visual appeal.
Depth of Field — it's the distance of the objects, from the camera's viewpoint, that are considered to be clearly focused. If objects that are near and far from the camera are both in focus, this is said to be large depth of field. If only one object is clearly focused and everything in front of and behind it is blurry, this would be shallow depth of focus.
Field Camera — a view camera that is designed to be compact, portable and lightweight so that it can be used "in the field" instead of in the studio. A press camera is a good example of a field camera.
Focal-plane Shutter — see Shutters.
Folding Camera — a camera that collapses when not in use to make itself more compact. This is typically done by using flexible bellows and a hinged door that opens to provide the support for the lens. An example of a folding camera is my Kodak Pocket Brownie Model B.
Guide Number — used in flash photography as a way to calculate the proper exposure based on the film speed and distance from the subject; but it's also often used to compare the light output between two different flash units. Given the same film speed, the larger the guide number, the more light output there is.
The formula for using the guide number (GN) is: GN = f/stop x Distance. So for instance, if the f/stop is 8 and the distance is 12 feet, GN = 8 x 12, so GN = 72.
So you can use simple algebra to figure other things. Typically you know your GN (which is on the flash unit) and you can figure out the subject distance by focusing on it and reading the distance on the lens. Thus you can figure out what aperture to set. Example: the subject distance is 12 feet and your GN is 48. f/stop = GN ÷ distance, so f/stop = 48 &mdivide; 12, so f/stop = f4.
Guide numbers change depending the film speed (since faster film responds to light much faster) what angle of coverage is needed (a flash that covers a 28mm lens spreads light wider (and thus less far) than a flash that was meant to cover a 50mm lens), and whether you're measuring distance in feet or meters. If you compare two different flash units, you need to make sure they cover the same angle and the ISO/ASA speed (or DIN) is the same, or your comparison won't be valid.
Hot Shoe — see Shoe.
Leaf Shutter — see Shutters.
Light Meter — a tool that measures the amount of light striking the censor, which can then be read and interpreted to adjust the camera for exposure. Human eyes constantly adjust to different light levels so it's difficult for people to make clear judgements about brightness. A good light meter is "unbiased" or "uninfluenced" by subjective human senses.
The earliest light meters were hand-held, separate accessories. It wasn't until after World War 2 that they began being incorporated directly into cameras in large numbers. The earliest on-board meters were uncoupled, meaning they worked independently of anything else on the camera. Later meters were coupled to the aperture, shutter or both, so that they could give better readings and even take automatic control of the camera.
Earlier meters had external sensors, such as on my Canon RM, but by the mid-60s the better cameras had changed to through-the-lens (TTL) metering, whereby the sensor was inside the camera and measured the light that passed through the lens—thereby giving the meter much the same light levels that the film would see. A few cameras, such as the Olympus OM-2, offered off-the-film (OTF) metering, whereby the meter read the light that actually struck the film (most others read light level from the focusing screen).
Movements — describes the action of moving sections of the camera to produce special effects. Nearly all view cameras have movements, which is what makes them so versatile; field cameras and press cameras usually have some movements. On most cameras, the "back" of the camera, the part that holds the film, and the "front" of the camera, which holds the lens, are fixed in relation to each other; sometimes the front moves forward and backward to focus the image, but that's it. But a camera with movements allows one or both of these sections to move independently of the other.
There are three main movements on a camera: tilt, swing and rise/fall. Tilt is where the front or rear of the camera is allowed to point upward or downward, as if there were an axis running horizontally through it. Swing is where the front or rear of the camera is allowed to turn right or left, as if there were an axis running vertically through the center of it. Rise and Fall allow the front or rear of the camera to phyiscally rise above or fall below the center of the other.
Meniscus lens — a lens with only one element (or piece of glass). Two or more elements combined together make a compound lens. Meniscus lenses are found in very old, very inexpensive cameras like a Brownie box.
Off-the-Film (OTF) Metering — see Light Meters
Packard Shutter — see Shutters.
Press Camera — a camera that was designed or used primarily by newspaper and magazine photographers. They were designed to be relatively lightweight, rugged, and extremely versatile. Press cameras were very popular in the early through mid—20th century, but were made obsolete by the system cameras that became popular in the 1960s. The ubiquitous example of a press camera would be my Speed Graphic.
Program Mode see Automatic Exposure
Rangefinder — a tool that determines the distance from the viewer to a target. On cameras, a rangefinder is typically tied into the camera lens so that when the rangefinder determines the distance to the target, the lens is focused at that distance. Rangefinder is also typically used to describe a camera that has the rangefinder tool built in. Rangefinder is also erroneously used to describe any camera that looks like a rangefinder camera, regardless of whether or not the camera really has the tool. Example: my Voigtländer Vito B would be commonly called a rangefinder because it looks like that kind of camera, even though there is no rangefinder capability on it.
Reflex Camera — once a very common designation for any camera that used a mirror in its viewfinder, such as a Single Lens Reflex or a Twin Lens Reflex. Camera makers typically appended a trade name with the word flex, hence such cameras as the Graflex and the Rolleiflex. The "F" in the Nikon F supposedly stands for "flex."
As marketing terms, reflex and flex are obsolete.
Resolution — the abilility to distinguish two similar objects that are next to each other. Resolving power is important in both optics and digital sensors. In lens optics, resolving power is typically measured in lines per milimeter: a number of parallel black lines are printed on white paper, grouped so that each group has more lines within the same area. The more lines that are crammed into the area, the closer they have have to be. At some point the lens will no longer be able to render the clearly white space between the lines: this is the limit of the resolution. Obviously, the higher the resolution, the better the lens will be at producing an apparently sharp and detailed image.
In digital sensors, resolving power is typically measured as a two-dimensional pixel area. Given two sensors that are physically the same size, the sensor with more pixels would be able to capture more detail in an image than a sensor with fewer pixels.
Screw Mount — a method of attaching a lens to a camera. The end of the lens and the receptical on the camera-body are both threaded, and the lens "screws" into place. Very popular in the 1950s and 1960s, but dropped in favor of bayonet-mount for a variety of reasons. The "Pentax Universal" mount, also known as the "M42," and the Leica "M39" are the most common.
Shoe — a bracket mounted on the camera that's used as a mount for accessories—most often electronic flashes. These typically began appearing in the 1950s (prior to that, the accessory was mounted on a bracket that screwed into the tripod mount in the bottom of the camera) and were called accessory shoes, because flash attachments and light meters were often mounted. In the 1960s as light-meters began being incomporated into the camera itself, the shoe mounted flash units pretty much exclusively.
When the electronic flash unit became standard, camera-makers began changing the shoe to add electrical contacts that matched with a specially-designed flash unit's foot, so that the flash could sync with (and later set) the camera instead of having to be plugged in via a cord. Shoes with electrical contacts became known as hot shoes, and are so common now people often call them hot shoe regardless of whether they're really hot or not.
Shutter — a mechanism used to regulate the amount of light that passes through the camera and strikes the film. Shutters are measured in time, typically in fractions of a second. The smaller the fraction, the less light strikes the film. (Digital cameras do not typically use shutters, but use "shutter speed" to describe how much time the digital sensor uses to record the image.
Shutter speeds affect the amount of motion blur introduced while the film or digital sensor is being exposed. Shorter shutter speeds mean the image has less of a chance to move, and thus one tends to get a sharper image. Longer shutter speeds allow for more blur.
There are three major kinds of mechanical shutters on film cameras: blade, leaf and focal-plane:
Blade shutters have something like a guillotine action: a large window (larger than the largest-possible aperture) is cut into a piece of material and spring-loaded to sit near the aperture. When fired, the shutter-hole crosses in front of the aperture and allows light to enter as long as the shutter hole passes across the aperture. They are very simple but not very versatile. My Brownie Target 616 has a blade shutter in it, as do many cheap cameras.
Leaf shutters work the same as apertures except that the hole closes completely, and is typically located in-between elements of the lens. Leaf shutters were and are very popular on mid-priced to expensive cameras, and they are very quiet. My Busch Pressman Model C has leaf shutter.
focal-plane shutters work similar to a blade shutter in that a window moves across the film to allow and interrupt the exposure. focal-plane shutters get their name because they are located in the rear of the camera just in front of the film (where the image focuses, ergo the "focal plane"). Because the film is shielded even though passes through the lens and across the length of the camera, a mirror can be set in-between and the photographer can see the same image that the film would see. focal-plane shutters are used in single lens reflex cameras for this reason. They are also very fast, typically faster than all but the best leaf shutters; unfortunately, they are also louder. All of my SLRs have focal-plane shutters, but so does my Graflex Junior.
The difference between a focal-plane shutter and a blade shutter is that the latter's window is fixed; the former is typically two pieces that abut together: one piece rolls across the film to allow exposure, then the second rolls across to end complete it.
There are also Packard shutters, which are not used on new cameras anymore but are still available on old cameras. Packard shutters sit behind the lens and are similar in action to a blade shutter. However, wheras a blade shutter crosses the aperture and that's it, the Packard shutter crosses in front of the aperture, stays there for a given time, and then retreats back to its closed position. The shutter time is controlled by a cable or an air hose connected to a bulb, so that the shutter opens for as long as the photographer squeezes the bulb.
Packard shutters, because they sit behind the lens, can be used with a variety of different kinds of lenses, whereas a leaf shutter is typically mounted in-between the lens elements. This makes them popular for use on very old cameras and very old lenses. Sadly, I do not have a camera with an example of a Packard shutter. Packard shutters were made obsolete by focal-plane shutters.
Shutter Priority see Automatic Exposure
Single Lens Reflex (SLR) — a viewfinding method where the image passes through the same lens that will expose the film, so the image should be the same. Good examples in my collection include the Canon AE—1 and the Nikkormat FTN.
Stereo cameras — a camera that takes at least two images simulatenously, so that when viewed simultaneously, each of the viewer's eyes sees a different, corresponding image. Because the brain interprets depth as the differences between the images seen by each eye, the brain looks at the stereo photographs' differences and infers depth. Often called three-dimensional or 3D photography. I have several stereo cameras, including the Kodak Stereo and the View-Master Personal.
Stereo photography was a fad in the late 19th and early 20th centuries using the Holmes stereoscope, and again for a brief time in the mid-20th when Realist format slides were introduced. Stereo photography is a small niche interest among amateurs, but it still used by the military and scientists in landscape photography.
System Camera — a camera, or more often a family of cameras, that was designed to take a wide range of accessories, such as lenses, automatic winders, motor drives, flash attachments of various sizes and configurations, view—finder accessories, and so on. While cameras were made earlier that had a lot of accessories, the Japanese SLRs of the 1960s exploded their popularity. A good example of a system camera is my Canon F–1.
Through-the-Lens (TTL) Metering — see Light Meters
Twin Lens Reflex (TLR) — a viewfinding method where two identical lenses are used, one located as close to the other as possible; one lens would expose the image on the film, the other lens would be used for composing the image. A good example in my collection would be the Rolleiflex Automat and Voigtländer Brilliant.
View Camera — Generic term for a camera that has two sections, a rear section to hold the film and a front section to hold a lens, and a set of extending bellows in—between. The image is focused onto a ground glass at the rear of the camera, then moved out of the way when the film is placed in position. View cameras are typically large and not very portable, but are extremely versatile and can do many things that other cameras cannot. They are still widely used by professionals, and are now fitted with digital sensors instead of film. An example would be my 4x5 Ansco View.
Viewfinder — a tool that tries to show the photographer what the film will see as an aid to composing the image. On older cameras, a viewfinder is only a composition tool; on more modern cameras, the viewfinder is combined with a focusing aid (like a rangefinder and exposure controls.