Camera Terms and Acronyms for Dummies

[Actor]

Quote: Originally Posted by Jaszek

Quote: Originally Posted by Bakko

wow awesome threat!
helped a lot, thanks for taking the time to do this =]

I think you mean thread lol.

Quote: Originally Posted by Dao

HSM: Hyper-Sonic Motor (Sigma Lens)
USM: Ultrasonic Motor (Canon Lens)
VC: Vibration Compensation (Tamron Lens)
EOS: Electro-Optical System (Canon Camera series)
EF: Electro-Focus (Canon Lens)
EF-S: Same as EF, S stands for "short back focus" (Canon Lens)

Thanks, added. Anything else?

18% gray, 645, 6x6, 6x7, 80 series filter, 85 filter, agitation, air bell, APS, ASA, bellows factor, bounce flash, bulb(both definitions), burning, catadioptric, CCD, chromogenic, circle of confusion, clearing time, color temperature, condenser head, confirmation border, contact print, contact sheet, critical aperture, daylight balanced film, densitometer, density, develop, developer, developer capacity, dial thermometer, diffusion head, DIN, diopter(both definitions), dodging, dry side/wet side, easel, emulsion, emulsion to emulsion rule, enlarger, EPA, exposure index, fb+f, fibre-based, fill flash, film apron, filter, filter factor, fixer, FL-B filter, FL-D filter, focal plane shutter, fog, gauge, glass, glass thermometer, gray card, gray market, guide number, halation, handheld rule, hypo, hypo clear, incident light vs. reflected light, inverse square law, ISO, large format, latent image, leader, leaf shutter, loupe, magazine, maximum black, medium format, negative carrier, neutral density, orthochromatic, panchromatic, parallax, pentaprism, photo-flo, pinhole(both definitions), proof sheet, pull, push, reciprocity, reciprocity failure, reel, resin-coated, reticulation, reversal film, safe light, shutter, shutter speed, split image, spot meter, stop(both definitions), sunny 16, surge line, tank, tempered, toe, transmittance, transparency, tungsten balanced film, T-stop, view camera, washing aid, wetting agent, WLF, work for hire, zone system.

[Jessmica]

Wow, this is so helpful! My college tutors really sucked at explaining all of this
Thanks

[Actor]

18% gray
A gray color midway between black and white, corresponding to Ansel Adams' Zone V. Light meters are calibrated using the assumption that whatever is being metered averages to 18% gray. In fact most scenes do average to 18% gray but there are exceptions, such as scenes with a lot of snow or scenes with a lot of black. The origin of the term is unclear. See gray card, Zone System.

645, 6x6, 6x7...
In medium format photography a designation of the size of the image on the negative, i.e., 6cm x 4.5cm, 6cm x 6cm, 6cm x 7cm. Other sizes are also common in the format. See medium format.

80 series filter
A series of blue filters designed to allow daylight balanced color film to be used under tungsten lights. These filters attenuate the light by two stops. See daylight balanced, tungsten lights, stop.

85 filter
An amber filter designed to allow tungsten balanced color film to be used under sunlight or most forms of flash. It attenuates light by 1/3 stop. See tungsten balanced, stop.

agitation
The act of frequently inverting and tumbling a tank in order to bring fresh developer into contact with the film. See tank, developer.

air bells
Bubbles that form on film when solutions are poured into the tank and show up as spots on the negative. These can be dislodged by lightly rapping the tank on a counter top.

APS
Abbreviation for Advanced Photographic System, a 25mm gauge marketed by Kodak with limited success.

ASA
Abbreviation for American Standards Association, commonly used for their ratings of film speed. The rating is directly proportional to the amount of exposure needed to darken the negative, with correct processing, to 18% gray. See 18% gray.

[Flo]

thank you guys for the class....confused but im sure after the cloud of words i will prevail...thanx!!

[musicaleCA]

Regarding 18% grey, the term is derived, I believe, from the approximate percentage of black pixels/dots that need to be present on a white media (say, paper) for our eyes to perceive it as a mid-tone, neutral grey.

[Actor]

Quote: Originally Posted by musicaleCA

Regarding 18% grey, the term is derived, I believe, from the approximate percentage of black pixels/dots that need to be present on a white media (say, paper) for our eyes to perceive it as a mid-tone, neutral grey.

The "approximate percentage of black pixels/dots that need to be present on a white media (say, paper) for our eyes to perceive it as a mid-tone, neutral grey" is 50%.

The term is a misnomer. Take a checkerboard pattern of black and white squares. This will meter as 18% gray yet the ratio of black to white is 1:1, i.e., the ratio of black:total = 50%, not 18%. If you back off from the checkerboard until you can no longer see the individual squares then your eyes will perceive it as 18% gray.

It should be called 50% gray, yet for some unknown reason, convention dubs it 18% gray. There does not seem to be any scientific basis for the use of 18%.

[musicaleCA]

Damn crazies. >.<

[Actor]

bellows factor
A compensation in exposure when the subject is very close to the lens. “Very close” is usually taken to be within ten focal lengths.

bounce flash
The practice of aiming a flash unit at an intermediate reflecting surface, such as the ceiling, a wall, or a white screen, instead of at the subject. It’s purpose is to create a softer light. See soft light.

bulb
1. A setting on a camera’s shutter speed control, which causes the shutter to remain open as long as the shutter button is held down. Its purpose is to create long exposures that are not available on the camera’s normal range of shutter speeds. The term derives from a remote shutter release that uses air pressure. The operator opens the shutter by squeezing a rubber “bulb” at the end of a pneumatic hose.
2. A small light bulb containing a flammable metal in a pure oxygen atmosphere. When the metal is ignited by an electric current the metal burns with an intense light lasting 1/30 second, peaking at 1/60 second. It’s chief disadvantage is its expense since each bulb is good for only one exposure. Generally no longer used.

burning
A darkroom practice of making certain parts of a print darker by exposing them longer while shielding other parts of the print from light. See dodging.

camera
Latin for room.

camera obscura
Latin for dark room. Historically, a room with a pinhole or lens on one side. A person standing in the room could see an inverted image of the scene outside. See pinhole.

catadioptric
A means of forming an image with a combination of a parabolic mirror and a hyperbolic mirror. Sometimes called a “mirror lens,” it is not actually a lens at all. Mirror lenses are free of chromatic aberration. See chromatic aberration. Google Schmidt telescope.

CCD
Abbreviation for Charge Coupled Device. It’s the chip which replaces the film in a digital camera.

chromogenic
Black and white film designed to be processed in color chemistry.

circle of confusion
An area on a negative or CCD over which a point of light can be spread and still be accepted as being in focus. The larger the circle of confusion a user is willing to tolerate, the more depth of field is available to him. See depth of field.

clearing time
A test for checking whether used fixer is still good. A piece of unexposed film is placed in the fixer and the time it takes for the film to turn clear is measured. The time is takes to fix a negative is twice the clearing time. See fix, fixer.

color temperature
The temperature of a source of light, usually given in degrees Kelvin. Tungsten lamps have a color temperature of about 3400 degK, daylight and strobe flash have a color temperature of about 5000 degK. The color temperature of a light source loosely indicates how its colors are distributed across the visible spectrum. Sources with low color temperatures don’t have much blue light. Sunlight has a high color temperature and can generally be regarded as having an equal mix of all colors (an astrophysicist may challenge that, but for photographic purposes the concept works). Digital photographers deal with color temperature by adjusting white balance. Film users have a bigger problem requiring them to select a film balanced for the kind or light they are using and/or using a filter to balance the light to the film they are using. Most print film is daylight balanced, which matches daylight and strobe flash. An 80 series filter is needed if this film is used under tungsten light (household incandescent or floodlight), an FL-D is used under fluorescent light. Some tungsten balanced film is available. This needs an 85 filter if used under sunlight or strobe flash. An FL-B is used under fluorescent light. Black and white shooters can generally ignore the problem of color temperature.

condenser head
A light source for an enlarger, which uses a lens to get light to strike the negative a right angle to its surface. The makes for a sharper print but enhances scratches and dirt.

confirmation border
The border of a print, which includes not only the image, but also the area of the negative that is immediately outside the image, thus confirming that the entire image has been printed.

contact print
A print made without use of an enlarger by placing the negative in contact with the paper and exposing it to light. See emulsion to emulsion rule.

contact sheet
A sheet containing a contact print for every frame on a roll of film.

critical aperture
In a lens with adjustable aperture, that aperture which gives the sharpest image.

[Actor]

daylight balanced film
Film designed to correctly reproduce colors when exposed under daylight.

densitometer
An instrument for measuring the density of processed film.

density
The darkness of a negative at a given point.

develop
The process of enhancing a latent image on film to the point of making it visible. This is done by causing the film to react with a chemical called developer.

developer
A chemical used to develop film.

developer capacity
The area of film that can be developed with a given volume of developer.

dial thermometer
A thermometer which indicates temperature on a dial instead of a linear scale.

diffusion head
An enlarger head designed to cause light to strike the negative from many different angles. It minimizes the effect of dust and scratches on the negative but does not produce an image as sharp as a condenser head. See condenser head.

DIN
Abbreviation for Deutsches Institut für Normung (German Institute for Standardization). For film speed the DIN scale changes 3 units per stop. The relationship between ASA and DIN ratings is DIN = 21 + 3* LOG(ASA/100) where the LOG is base 2.

diopter
1. The reciprocal of the focal length, in meters, of a lens.
2. A lens in front of the viewfinder of a camera which allows the user to see the image without wearing glasses. In some camera this is an adjustment built into the camera. In others must order the diopter ground to his/her prescription.

dodging
Making certain areas of a print lighter by masking them from the enlarger.

dry side/wet side
A design for a darkroom in which the area with the sink, plumbing and liquid storage is kept isolated from the area with the enlarger and supplies which need to be kept dry.

[dxqcanada]

Grey Card - grey coloured card that uniformly reflects 18% of the light which falls upon it, used to calibrate exposure.

[Actor]

Quote: Originally Posted by dxqcanada

Grey Card - grey coloured card that uniformly reflects 18% of the light which falls upon it, used to calibrate exposure.

I can find no reference which verifies that a gray card reflects 18% of the light that falls upon it. If you can cite some source that gives a scientific justification for the use of 18%, I'd like to know what it is.

We know that a gray card will meter the same as a black and white checkerboard, provided that an equal number of black and white squares are metered. This implies that both a gray card and a checkerboard have the same reflectance, videlicet, 18%. A natural assumption is that black has a reflectance of 0, therefore, white must have a reflectance of 36%.

Proceeding logically from there leads to a mathematical paradox.

If you take a (properly metered, exposed, and processed) picture of a gray card you get a negative that matches the gray card, as does a print made from that negative. All three, the gray card, the negative and the print, will be Zone V. For the sake of argument let's suppose that the combination of shutter speed, aperture and film speed was such that 1,000,000 photons had to pass through the lens to produce this negative. Now let's suppose that we have a card that is Zone VI. If we wish to produce a Zone V negative and print by taking a picture of this Zone VI card we have to reduce exposure by one stop, say be reducing the time the shutter is open by half. But to get a Zone V negative we still need 1,000,000 photons, which implies that the Zone VI card must have reflected 2,000,000 photons. That means a Zone VI card must have a reflectance of 36%.

But have we not already established that white (Zone X) has 36% reflectance?

Therein lies the paradox. Obviously, there's a flaw in the logic somewhere, but where? If you can enlighten me, I'd be grateful.

The maximum a white card (Zone X) could reflect is 100% of incident light, then a Zone IX card would reflect 50%, Zone VIII 25%, Zone VII 12.5%, Zone VI 6.25% and Zone V (gray card) 3.125%. There's no way a gray card reflects 18% of incident light.

[Steph]

Quote: Originally Posted by Actor

We know that a gray card will meter the same as a black and white checkerboard.

Do we? Anyway your argument is flawed. A light meter in a camera is calibrated to render what it meters medium grey (usually around 18% reflectance). If you fill the frame with a white page, a black page or a grey card and let the meter to its own device you will get exactly the same result: a 18% grey image. 18% is used as it is considered to be the reflectance of an average scene. You are over-complicating when talking about the zone system. The explanation is in how a light meter works.

[Actor]

Quote: Originally Posted by Steph

Quote: Originally Posted by Actor

We know that a gray card will meter the same as a black and white checkerboard.

Do we?

Yes. I've verified that experimentally. I admit it's a surprising result. By the way, if you want to verify it yourself make certain that the black squares are maximum black, Zone 0, or you'll find the the checkerboard reflects more than a gray card.

Quote: Originally Posted by Steph

Anyway your argument is flawed.

Precisely. As I pointed out, it leads to paradoxical conclusions, meaning either that the assumptions are wrong or that there's a non sequitur in the argument. We need to find where it breaks down. I don't think the checkerboard axiom is it.

Quote: Originally Posted by Steph

A light meter in a camera is calibrated to render what it meters medium grey (usually around 18% reflectance).

External light meters measure luminous intensity, usually in some ad hoc units. Most then provide a circular slide rule devised to calculate, for a given film speed, a combination of shutter speeds and apertures which will give a medium gray negative. Internal meters have a linkage to the camera's workings which do the same thing automatically. Sans the slide rule or the linkage, light meters simply measure luminous intensity. (Actually, they don't measure luminous intensity as the SI defines it, but for our purposes here the difference is so trivial that I won't go into it.)

The point here is that if you point a light meter at a gray card and write down the reading, then point it at a known Zone VI card, you'll get a higher reading. The difference between the two readings, whatever they are, is one stop. Go back and read my closing argument again.

Quote: Originally Posted by Steph

You are over-complicating when talking about the zone system.

But, complicated or not, if a concept is inconsistent with the Zone system then either the concept or the Zone system is wrong. Since the Zone system has been working since 1940 it's more likely that the concept is wrong. The concept, in this case, is the idea that a gray card has 18% reflectance.

[Steph]

Actor, I read your initial post again (carefully this time) and I now understand what you are asking (and I now see that my answer was useless). I'll need to think about it a bit more; as it stands, I cannot actually find the flaw in your argument.

[Actor]

easel
A fixture for masking off the edges of photographic paper in order to produce a white border on the print. Usually adjustable.

emulsion
1. A suspension containing the light sensitive chemicals of film or paper.
2. The side of the film or paper holding said suspension.

emulsion to emulsion rule
In making a print the emulsion side of the negative should be toward the emulsion side of the paper.

enlarger
A device for focusing an image on a negative onto photographic paper in order to make an enlarged print. It is basically a camera in reverse.

EPA
Abbreviation for Environmental Protection Agency. Woe unto he that flushes the wrong chemicals down his toilet.

exposure index
The "effective film speed" assigned to a particular film by a photographer. Typically the photographer would begin with the film speed assigned by the film's manufacturer and then adjust it according to his own experience or experiments. For example he might assign a speed of ASA 320 to a film marketed as ASA 400 because he believes the lower number gives better results.

exposure value
A system which combines aperture and film speed into a single value. EV is related to aperture and shutter speed by the formula

EV = log(A^2/t)

where A is the aperture (f number), t is the shutter interval in seconds and the log is base 2. E.g., is the aperature is f/2 and the shutter speed is 2 (a shutter interval of 1/2) then the EV is 3.