+- Twitchin Kitten - conversation community (https://twitchinkitten.com)
+-- Forum: Art & Entertainment (https://twitchinkitten.com/forum-31.html)
+--- Forum: Photography & Art (https://twitchinkitten.com/forum-32.html)
+--- Thread: A - Z of Photography (/thread-20.html)
A - Z of Photography - Twitchin Kitten - 08-13-2009
I'll be adding the completion of this little by little, but for right now I want to get things rolling so patience is a virtue!
A
Agitation
Agitation is a necessary part of film and paper processing and works by moving new chemistry in and around sensitive material.
All films processed in developing tank are based on set developing times and rates of agitation.
When films are not agitated the result will be uneven processing and under development.
Aliasing
In Digital photography CCD sensors create square shaped pixels.
Unfortunately square pixel can’t describe curved shapes very well and when viewed close up look jagged.
Aliasing is more noticeable in low resolution images but less so in higher resolution images due to the increase in pixel numbers.
To counteract this camera manufacturers place an anti aliasing filter between the lens and image sensor to reduce the visible effects.
A by product of this is slight reduction in contrast.
Ambient light
A continuous light source that unlike electronic flash isn’t transitory. Ambient light is measured by a traditional in camera or hand held light meter. Ambient light forms the basis of all timed exposures but can be of variable colour temperature
Aperture
The aperture is a variable opening inside a camera lens that lets pass through onto film or in a digital camera the CCD sensor.
Aperture numbers are in an internationally recognized scale measured in F numbers.
These numbers are typically arranged as follows
f/2.8,f/4,f/5/f/5.6,f8,f/11,f/16,f/22.
Aperture values are primarily designed to moderate the varying intensity of light
to enable successful exposures.
Wider apertures such as f/2.8 let in the maximum amount of light compared to narrow apertures such as f/22, which let in the least amount of light. Aperture values can also influence depth of field.
Aperture priority mode
This is the most popular auto exposure option found in SLRs and better compact cameras.
Aperture priority works when the photographer defines the aperture field and the camera sets the right shutter speed to make a correct exposure.
Aperture Priority is useful when you want to create a particular depth of field effect.
APS (Advanced Photo System) Format
The APS photo system is designed to give a choice of 3 different print shapes on the same roll of film. APS films can only be used in APS compact cameras which are easily identified by the triangular logo.
Unlike 35mm APS is loaded and rewound automatically via a special loading compartment once processed the film is stored in the cassette for safekeeping. Designed primarily for amateur and family use, APS cannot be enlarged like 35mm film without a noticeable reduction in image quality.
Auto Exposure
Found on most compact and SLR cameras the auto exposure mode is a convenient tool if you don’t want to keep manually controlling exposure.
With this type of setting the camera automatically selects both shutter speed and aperture value so precise control over depth of field and movement cannot be guaranteed.
Auto flash
Most digital and 35mm compact cameras have an auto flash function which fires when light levels are too low for a normal exposure.
A disadvantage of auto flash is the loss of control over its intensity and direction resulting in snapshot type photos.
Much better results are produced using manual flash modes or and external hammerhead flashgun.
Auto focus
Auto focus cameras take the human error out of focussing a lens. With this system most compact cameras focus on the object in the centre of your frame, which can cause a problem if your composition is off centre.
Better SLRs have multi zone auto focus systems which can respond to more creative framing. Autofoucs works best when locked onto an area with sufficient contrast.
B
Backlighting
If your subject is arranged against a background of intense light such as a portrait in front of a window, auto exposure will record this as an image.
Use fill flash to lighten up the sitter in the foreground or use a reflector to reduce the difference in contrast
Barrel Distortion
Found most frequently when using wide angle lenses, Barrel distortion causes parallel lines to converge at the edge of the film frame. Top quality lenses tend to suffer less from barrel distortion and worst offenders are low grade zoom lenses used at their wide angle settings.
Bit depth
Sometimes called colour depth, bit depth describes the size of colour pallet used to create a digital image 8 bit, 16 bit, and 24 bit are common pallet sizes creating 256 , several thousand, and 16.7 million colours respectively
Bitmap Image
A bitmap is a common term for a pixel based image. Also called a raster image, this describes a grid of pixels arranged in a checker board like arrangement.
Blower Brush
A useful tool for removing dust and hair off lenses and negatives.
The blower brush is used instead of physically touching delicate surfaces which could easily be damaged.
Dust on both enlarger and camera lenses lowers the quality of the final image and must be removed regularly to ensure best results.
On no account should a lens be rubbed with a household cleaning cloth as this will result in the removal of lens coating.
Blurring
Blurred images are frequently caused by camera shake caused by slight body movement during exposure. Coupled by a slow shutter speed, this will cause your lens to shake during exposure.
The problem is more noticeable in low light situations, but this can be solved using a tripod.
Always use at least 1/125s and 1/250s with long telephoto lenses
Bracketing
Used by professional photographers, bracketing is an insurance against uncertain exposure conditions.
Instead of gambling on one single frame, several identical versions of the image are taken, each with a different exposure variation.
After processing the best frame for printing or reproduction can be selected. This example shows six variations on one subject.
Bulb Setting
Despite the term the Bulb setting has nothing to do with flash photography.
Marked as a B on your shutter speed scale, it keeps the shutter open for as long as your finger keeps the shutter release pressed down.
Bulb is used at night time to make moving car headlights record as luminous stripes
Burning in
A technique used in the dark room for adding extra exposure to a section of a photographic print. Burning in commonly occurs through a small hole cut in a larger piece of card designed to protect the print from darkening.
Burst Rate
In digital camera technology, the term burst rate indicates the speed at which a camera can save and store image data, then get ready to capture the next shot
Better cameras with onboard memory chips can shoot at a fast rate/
C
C41
A universal process used for developing colour negative and chromogenic film.
The C41 process is the same worldwide and offers the convenience of identical processing times for all film types regardless of their ISO speed.
Card Reader
A card reader is a small device used to transfer digital card data to a computer. After removing the card from the camera, it is inserted into a card reader which is permenantlly connected to a computer.
This kind of device is essential if camera upload software is incompatible with an older computer, or when faster data transfer is desired from a camera which has a slower serial port connector. There are various forms of cards and card readers.
CCD
CCD stands for Charge Coupled Device and is the light sensitive sensor used in place of film in a digital camera.
A CCD is like a honeycomb of tiny individual cells with each other creating an individual pixel.
CCD sensors are sold with different recording capabilities described in mega pixels, or million pixels, such as a 3.34M Camera
CD-R
Compact Disc Recordable is most cost effective kind of storage media used in digital photography. Despite the low cost you need to have a cd writer to write data to a CDR disk, but they can all be played back on standard CD-ROM drive
Chromogenic Film
A special monochrome film based on the same emulsion used in colour negative film.
Very fine grain and not prone to excessive density through overexposure, films such as Ilford XP2 are good multipurpose materials.
Unlike other monochrome films chromogenic films can be processed in C41 chemistry, found in any shopping mall photo processors.
Enlargements from 35mm chromogenic film can be made larger than normal films of a similar speed.
Clip Test
Cyan, Magenta, Yellow and Black (Described as K to avoid confusion with Blue) is an image mode used to prepare digital photographs for commercial lithographic printing. All magazines and books are printed with CMYK inks, which have a smaller gamut than the RGB image mode.
CMYK Inks
CMYK inks are the standard colours used in inkjet printers for mixing realistic photographic colours. Better inkjets have three additional colours: light magenta, cyan, and black for reproducing better skin tones
Colour Casts
Colour casts are unexpected tints that appear on photographs. Casts are generally caused by shooting under an artificial light source such as domestic tungsten light bulbs or fluresount tubes without flash.
With daylight balanced film this will result in orange and green casts respectively.
For professional use special colour correct ting filters can be used over the camera lens to counteract this problem. Digital cameras have an inbuilt automatic filtering system called the white balance function.
Colour Negative Film
(35mm Print Film)
The most popular form of photographic film used for wedding, portrait, press, sports and general amateur photography. Designed for use when a print outcome is required, the film is cheap to process and enlarge. Colour negative has wider exposure latitude compared to transparency material and is much more forgiving.
In medium-format colour negative is available in two variants: daylight, sometimes called type S and tungsten, sometimes called type L.
(120 Medium Format Roll Film)
Colour Space
In digital photography, different image modes such as RGB, CMYK and LAB are designed with colour characteristics called colour space.
Like different palettes a colour space is defined with unique characteristics and limitations. LAB is the largest colour space, with RGB next, followed by the much smaller CYMK space. When converting from a larger space to a smaller space, loss of original colour can occur.
Colour Temperature
An exact measurement of light colour expressed in the Kelvin (K) scale.
Measured by a handheld colour temperature meter during colour critical assignments, both daylight and artificial light can be corrected using filters.
Colour Transparency Film
Once the professionals favourite, but now being largely superseded by digital and colour negative, transparency is the hardest sensitive material to use.
With little more than a half stop margin of error, transparency is designed to be used in a reprographic workflow, where no enlargement or prints are required.
Used by magazines and advertising photographers, transparencies are developed in the universal E6 process by professional laboratories in a tightly controlled environment.
Compression
Crunching data into smaller files is called compression.
Without physically reducing the pixel dimensions of an image, compression routines devise compromise colour recipes for a larger group of pixels. Rather than individual ones.
JPEG is a commonly used compression routine
Contact Print
Sometimes referred to as a proof sheet, the contact print is a positive same size print made from colour or black and white negatives.
The contact sheet is made so you can decide which negatives are worth printing up.
Using a modern digital mini-lab, a smaller kind of reference sheet called an index print offers the same service albeit at a reduced size
Cropping
Images can be recomposed after shooting by a process called cropping.
Used to create visually stronger images, can occur during enlarging or mounting, Digital photographers can use a simple crop tool to remove unwanted pixels
D
Densitometer
There are two types of densitometer used in professional processing labs: the reflective and the transmissive.
The transmissive densitometer is used to measure the effectiveness of the developing stage in film processing.
The reflective densitometer is used to test development of print materials.
Both tests allow a lab manager to adjust processing times, chemical replenishment or processing temperature to ensure consistent results
Depth of field
The zone of sharpness set between the nearest and furthest parts of a scene.
You control DOF by two factors: your position to the subject and the aperture value selected on your lens. Higher f-numbers such as f/22 create a greater depth of field than lower numbers such as f/2.8
Development
Exposure of photographic materials creates a hidden and latent image which needs to be amplified by a process called development
Within the light sensitive emulsion, tiny silver crystals are enlarged by the developer until they become visible. Development is the first and most critical stage of converting a latent image
Digital Zoom
Used in digital compact cameras for pulling a distant subject closer, digital zoom is not to be confused with proper telephoto functions.
It works by enlarging a small batch of pixels by interpolation to make detail look bigger than it really was. Results from a digital zoom setting will show a loss of sharpness.
Dodging
Also called holding back, dodging is a darkroom term for limiting exposure in small areas of a darkroom print.
Used when areas of an original negative are thin and don’t hold enough detail to make a straight print, dodging is often carried out on the facial areas of location portraits.
Double Dark Slide
Used for holding sheet film ready for exposing in a view camera
(also known as a monorail camera), the double dark slide must be loaded and decanted in total darkness.
Designed with colour coded sides so you can remember which sheet has already been exposed, the double dark slide must be kept free from dust.
DX Coding
Most modern 35mm cameras use an automatic film-speed detection system called DX coding. Fitted with tiny electrical sensors inside the film cassette chamber the process works by reading the checkerboard pattern printed on the outer 35mm cartridge.
While designed to prevent exposure errors caused by setting the wrong film speed, many cameras are not able to override DX coded speed in order to uprate film speed.
In these circumstances, new checkerboard strips can be bought and stuck on the cassette to fool the camera.
Dynamic Range
The dynamic range is a measurement of the brightness range in both photographic materials and digital sensing devices. The higher the number the greater the range of captured tone from white to black.
E
E6
The standard processing sequence for colour transparency films.
Like C41 the E6 process is universal and can accommodate films of all speeds and formats in a single run.
Uneconomic to try at home, and difficult to maintain constant quality, the E6 service is best bought as a professional lab service.
Emulsion
The layer of photographic film which contains the light sensitive chemicals. Emulsion is a mixture of inert gelatine and silver halides, mixed together to form an even coating which is permeable during processing but stable when dry.
Exposure
Exposure is the amount of light that falls onto a digital sensor or light sensitive material.
In both photographic printing and shooting, exposure is controlled by a combination of time and aperture setting.
The term is also used to describe a single frame or shot taken
Exposure Compensation Dial
Used to set smaller third of a stop variations in exposure, the exposure compensation dial offers a precise way of controlling demanding subjects.
Sometimes referred to as the EV or +/- function, it offers smaller incremental change compared to exposure adjustments offered by the shutter speed and aperture scales especially on mechanical cameras.
[size=large]F [/large]
Fast Film
Films such as ISO 800 are designed to permit shooting in a low light situation or freezing fast moving subjects.
High speed film is manufactured with a light sensitive emulsion which needs much less light compared to standard ISO 100 film materials.
Fast lenses
Prime camera lenses designed with wider maximum aperture. Such as f/1.8 or f/2.8 are known as fast lenses.
Compared to mini-zoom lenses which are sold with a maximum aperture like f/4, fast lenses allow you to shoot in low light conditions, use faster shutter speeds and, most importantly present a much brighter viewfinder image to aid accurate focussing.
Filters
Glass, plastic or gelatine filters can be attached to a camera lens for adding a creative effect to your photograph.
For colour critical assignments, colour correction filters can be used to match lighting colour temperature with film stock
Filters work by absorbing or transmitting different wavelengths of light, thereby allowing some colours to pass through to the film whilst some are prevented.
Filter Factors
All creative and corrective filters work by changing the composition of both artificial light and natural daylight.
To compensate for the absorption of certain wavelengths, additional light is needed to ensure a correct exposure. All filters are supplied with corresponding filter factors which indicate how much extra exposure is required.
Filter factors of 2, 4, or 8 mean an extra 1, 2, or 3 extra stops of extra light.
Film recorder
A high quality digital output device which is designed to produce films from digital files.
Fitted with a tiny internal laser, digital data is beamed directly onto film to produce film negatives.
High resolution digital files can also be output to large format transparencies using this device.
Film Retriever
A clever device used to extract the film leader from 35mm without needing a light – tight loading room.
Once extracted three or four inches, the leader can be trimmed and pre loaded onto a developing to make for easier loading.
Fix
Fixing is the last chemical stage of film and paper development and provides two important functions: rendering the material insensitive to light and washing away any unprocessed emulsion. Before light sensitive film is fixed, unexposed and underdeveloped emulsion is still present and gives film a characteristic ‘milky’ appearance.
After fixing, film is clear and assumes a transparent state. The chemical residues of fix must be removed by thoroughly washing or staining will occur in forthcoming months.
Flare
When shooting into direct light such as the sun, lens flare will occur.
Flare looks like a series of translucent discs overlapping on your image, or a drastic white burst of light.
Caused by excessive light entering a lens which is not protected by a lens shade or hood, flare is impossible to remove.
All lenses have a specially designed shade which is shaped to prevent flare from occurring.
Cheap rubber or universal lens hoods will never afford proper protection against flare.
Flash
Electronic flash is calibrated to produce light of a consistent and neutral colour. Flash is created when an electrical current passes through a tiny tube which produces a rapid burst of light. Unlike continuous light, the light quality from a flash can’t be seen before the moment of exposure.
Flash meter
A hand-held device for measuring the intensity of flash light falling on a subject.
Camera meters are not equipped to measure flash and this must be undertaken with a separate meter. Flash meters can be operated in two principle ways: corded and non corded. With the corded method the meter is connected to the flash unit with a sync cable which is then test fired by the meter operator.
In the non corded method, no sync cable is required and the flash unit is fired with an extra pair of hands while the meter is held in place. Flash meters express an aperture reading only because the flash burst itself defines the time element of the exposure which is unaffected by any change in shutter speed.
F-Numbers
Aperture values are described in f-numbers, such as f/2.8 and f/16. Smaller f-numbers let more light onto your film or digital sensor and with bigger numbers less light.
Fogging
Fogging occurs in both film and paper materials when they are inadvertently exposed to light. Low light fogging can occur if a dark room or processing tank is not sufficiently light tight, producing a severe dark patch on your film making it impossible to print properly.
Fogging can also occur if you accidentally open the camera back before rewinding your film or leaving your canister on a sunny windowsill.