Glossary

A

Agitation

Moving the chemistry over the film or paper during processing, by inverting or turning a tank or rocking a tray. It replaces used chemistry at the surface with fresh, so development is even.

Aperture

The opening in a lens that controls the amount of light passing through. In darkroom printing, stopping the enlarger lens down a few stops improves sharpness and controls exposure without strong creative effect.

B

Bleach

A processing bath that turns developed silver back into a form the fixer can remove. Colour film and paper are bleached so only the dye image remains.

Bleach-fix (BLIX)

A combined bleaching and fixing solution used in colour printing and processing. BLIX removes metallic silver while fixing the image, simplifying RA-4 workflows by replacing separate bleach and fix baths.

Backing Paper

A protective paper strip that wraps around 120 roll film, shielding it from light and providing frame numbering for various medium format cameras. The backing paper extends beyond the film at both ends. The extra length is what you thread onto the take-up spool.

Key functions of 120 backing paper include:

• Light protection: prevents accidental exposure before and after shooting.
• Frame markings: printed numbers correspond to different format sizes (e.g., 6x4.5, 6x6, 6x7).
• Guidance for loading: arrows and markings assist in aligning the film correctly in cameras without automatic film counters.

Unlike 35mm film, 120 film does not have perforations or a canister, relying entirely on the backing paper for handling and frame registration.

Bleach Bypass

Bleach bypass is a film processing technique that retains the silver halide layer in colour film by skipping or reducing the bleaching step during development. This results in an image that combines both the colour dyes and the black-and-white silver image, producing a high-contrast, desaturated look with increased grain.

The technique comes from cinema, where it was used for a dramatic, moody look. It is also applied to C-41 and E-6 films in still photography. The intensity of the effect depends on how much bleaching is bypassed, with partial bleach bypass allowing some colour retention while maintaining higher contrast.

Box camera

Simple, fixed-focus cameras with a basic box-shaped design, typically made for affordability and ease of use. Box cameras were widely popular from the late 19th to the mid-20th century. They were the first cameras most households could afford.

Key characteristics include:

• Fixed-focus lens: optimised for subjects at moderate distances.
• Single shutter speed and aperture: often limited manual controls.
• Medium format film: many models use 120 or 620 roll film.

Box cameras are basic, and collectors and experimental photographers use them for exactly that reason. The simple lens gives a soft, slightly vignetted rendering.

C

C-41

The standard chromogenic process for developing colour negative film. C-41 negatives are typically printed on RA-4 colour paper.

Changing bag

A light-tight fabric bag with two elasticated sleeves for your arms. You use it to load film onto a developing reel in daylight.

Cross processing

Cross processing is the technique of developing film in a chemical solution intended for a different type of film than originally intended. The most common example is processing slide film (E-6) in colour negative chemicals (C-41). The result is high contrast, shifted colours, and heavy saturation.

This technique was historically an accidental result of lab processing errors but became a popular artistic effect in fashion, experimental, and alternative photography.

D

Developer

The chemical that reduces exposed silver halide crystals to metallic silver, making the latent image visible. Used in both film and paper processing.

Dodging and burning

Selective lightening (dodging) or darkening (burning) of areas during exposure under an enlarger to refine local tone and contrast.

Depth of field

The range of distances within an image that appear acceptably sharp. Depth of field is influenced by three main factors:

• Aperture: a wider aperture (lower f-number) results in a shallower depth of field, while a smaller aperture (higher f-number) increases depth of field.
• Focal length: longer focal lengths produce a shallower depth of field, whereas shorter focal lengths provide greater depth of field.
• Subject distance: the closer the subject is to the camera, the shallower the depth of field; increasing the distance enhances depth of field.

Diffraction

An optical phenomenon that occurs when light waves bend around the edges of an aperture, reducing image sharpness. Diffraction becomes more pronounced at very small apertures (high f-numbers), causing fine details to appear softer.

While stopping down the aperture increases depth of field, excessive diffraction can counteract the benefits by degrading overall resolution. The optimal balance between depth of field and sharpness depends on the lens design, film format, and shooting conditions.

Dry-down

The change in a print's look as it dries. Black & white prints dry slightly darker than they look wet, and colour prints dry slightly lighter and warmer. Always judge a print dry.

Dye couplers

C-41 dye couplers are chemical compounds embedded in colour negative film that form visible dyes during the C-41 development process. These couplers react with oxidised colour developer to produce cyan, magenta, and yellow dyes. Those three are the complementary colours of red, green, and blue.

Each layer of C-41 film contains dye couplers specific to its sensitivity to light:

• Cyan dye couplers in the red-sensitive layer
• Magenta dye couplers in the green-sensitive layer
• Yellow dye couplers in the blue-sensitive layer

How the couplers are formulated sets the film's colour balance, contrast, and tonal character. It is what makes one C-41 stock look different from another.

DX coding

A chequered pattern of silver and black squares printed on most 35mm film canisters. Cameras with DX contacts read it and set the film speed for you.

120 film has no DX coding, so its speed is always set by hand.

E

Easel

A hinged or masked frame that holds photographic paper flat and square under the enlarger. The blades set the borders and keep the image aligned.

Emulsion

The light-sensitive coating on film and photographic paper that contains silver halide crystals (and dye couplers in colour materials).

Enlarger

An optical device that projects a negative onto photographic paper to make a print. It consists of a light source, negative carrier, lens, and height/focus controls.

Exposure time

The duration the enlarger light exposes the paper. Controlled with a timer and balanced with aperture to achieve correct print density.

F

Fibre-based (FB) paper

Photographic paper with a paper fibre base. Favoured for rich tonality and archival permanence but requires longer washing and drying.

Film leader

The narrow, shaped strip of film that sticks out of a 35mm canister. You thread it onto the camera's take-up spool when loading.

On 120 film, the tapered end of the backing paper does the same job.

Film perforations

Small, evenly spaced holes along the edges of photographic film that assist with transport and registration in cameras and projectors. Perforations ensure smooth film advancement and precise frame positioning.

Different film formats use distinct perforation patterns:

• 35mm film: features perforations on both edges, with variations such as Kodak Standard (KS) and Bell & Howell (BH) perforations.
• 16mm and 8mm film: may have perforations on one or both edges, depending on whether they are single- or double-perforated stocks.
• Motion picture film: often has specialised perforation types tailored to specific camera and projection systems.

The camera's sprockets engage the perforations, which is what sets the spacing between frames and holds the film steady as it is exposed.

Filtration

The settings of the yellow, magenta and cyan filters in a colour enlarger head. Increasing a colour's filtration removes that colour from the light, so the print moves towards the opposite colour. It is also used to set contrast on multigrade paper.

Fixer

The chemical bath that dissolves unexposed silver halide crystals, making the image permanent and light-safe.

G

Grain

The fine, sandy texture in a film image. It comes from the tiny clumps of silver, or dye clouds in colour film, that make up the picture.

Faster film shows more grain. The developer and how large you print or scan also change how much you see.

Grain focuser

A magnifier used on the baseboard to view film grain and achieve critical focus when setting up the enlarger.

Graded paper

Black-and-white paper manufactured at a fixed contrast grade (e.g., 1 to 5). The chosen grade controls the overall tonal separation.

H

I

Incident light

Light that falls directly onto a subject from a natural or artificial source, without being reflected off other surfaces. Incident light is measured using an incident light meter, which reads the intensity of light before it interacts with the subject.

A reflected reading measures light bouncing off the subject, so its colour and texture affect the result. An incident reading avoids that, and is generally more accurate. This makes them particularly useful in studio photography and controlled lighting environments.

Instant camera

Cameras designed to produce self-developing photographs moments after exposure, using specialised instant film. These cameras contain a built-in developing process that eliminates the need for external processing.

Key characteristics of instant cameras include:

• Integral or peel-apart film: modern instant cameras use integral film (e.g., Polaroid, Instax), while older models may use peel-apart film.
• Automatic exposure and focus: many models are designed for ease of use with minimal manual controls.
• Built-in flash: often included to accommodate various lighting conditions.

Instant cameras give you a finished print within minutes, which is the whole appeal. The trade-off is cost per shot and no negative to reprint from.

ISO

How sensitive a film is to light, printed on the box and on the film canister. A low number such as ISO 100 needs plenty of light, and records fine detail with little grain. A high number such as ISO 800 copes with dim light, and the grain is coarser.

The speed belongs to the film rather than the camera, so it is fixed for the whole roll. Set the same number on the camera or on a handheld meter, so the reading matches the film you loaded.

Older cameras and film boxes may use the ASA or DIN scales instead. ASA numbers match ISO ones, so ASA 400 is ISO 400. DIN counts differently: ISO 400 is 27 DIN, and ISO 100 is 21 DIN.

J

K

L

Latent image

The invisible image formed in a light-sensitive emulsion when it is exposed to light. The exposure creates a small change in the silver halide crystals that is not yet visible.

The developer amplifies that latent image into a visible one. On film this gives a negative; on paper it gives a print.

Light meter

A device that measures light intensity to help determine correct exposure settings. Built into most cameras or available as separate handheld units.

M

Multigrade paper

Variable-contrast black-and-white paper that changes contrast in response to coloured filters in the enlarger. One box of paper covers the whole contrast range.

Medium format camera

A camera that uses film or a digital sensor larger than 35mm but smaller than large format (4x5 inches or larger). Medium format film comes as 120 and 220 roll film. The larger negative holds more detail, dynamic range, and tonal depth than 35mm.

Common medium format aspect ratios include:

• 6x4.5 cm (645 format): a balance between portability and image quality.
• 6x6 cm (square format): popular in classic twin-lens reflex (TLR) and modular cameras.
• 6x7 cm and larger: often used in professional studio and landscape photography for their high resolution.

Medium format cameras are favored for commercial, portrait, and fine art photography due to their superior image quality and distinctive rendering.

N

Negative

An image on film in which tones are inverted: light subjects appear dark and vice versa. Used as the source for producing positive prints on photographic paper.

Negative carrier

The component of an enlarger that holds the film flat and aligned in the light path during exposure.

O

P

Parallax

The difference between what you see in the viewfinder and what the lens records, on cameras where they are separate windows. Rangefinders, TLRs and most point-and-shoots work this way.

It only matters up close. The nearer the subject, the bigger the shift.

Photographic paper

Light-sensitive paper used to make prints in the darkroom. Available as resin-coated (RC) and fibre-based (FB) with various surface finishes.

Print tongs

Plastic or metal tools used to transfer prints between chemical trays without touching the emulsion, preventing damage and contamination.

Point-and-shoot camera

A compact, user-friendly camera designed for automatic operation with minimal manual controls. Point-and-shoot cameras typically feature:

• Fixed or zoom lenses: often with autofocus and automatic exposure settings.
• Built-in flash: for low-light photography.
• Motorised film advance and rewind: in film models.

They are simple, portable, and easy to use. That makes them a convenient choice for beginners and for everyday shooting.

Push / pull processing

A technique used creatively to achieve specific aesthetic effects or to adapt to challenging lighting conditions.

• Push processing involves extending development time to increase contrast and apparent sensitivity, typically used when a film has been underexposed. This can result in increased grain and higher contrast.
• Pull processing reduces development time to lower contrast and compensate for overexposure, often leading to finer grain and reduced density in highlights.

Q

R

RA-4

The standard chromogenic process for making colour prints from colour negatives. Uses a colour developer followed by bleach and fix (or BLIX) and requires precise temperature control.

Resin-coated (RC) paper

Photographic paper sealed with a polyethylene layer. Washes and dries quickly and is ideal for proofing and general printing.

Reticulation

A crazed, crackled pattern in the emulsion, caused by a sudden large change in temperature between processing baths or washes. It cannot be removed, so keep every bath within a few degrees of the others.

Rangefinder camera

A type of camera that focuses using a rangefinder mechanism. You align two images of the subject in the viewfinder, and the lens is then focused at that distance.

Rangefinders use no reflex mirror. Instead they have a separate optical viewfinder with a superimposed focusing patch, which aligns when the subject is in focus.

Key characteristics include:

• Compact, quiet operation: no mirror slap or blackout during exposure.
• Parallax error: due to the separation between the viewfinder and the lens, particularly noticeable at close distances.
• Interchangeable or fixed lenses: many classic rangefinders support high-quality prime lenses.

Rangefinder cameras are small, quiet and quick to focus by hand. Street and documentary photographers favour them for those three reasons.

S

Safelight

A light of a colour that photographic paper is not sensitive to, so you can see to work without fogging it. Red is the usual colour for black & white paper. Colour paper needs complete darkness.

Stop (exposure)

A doubling or halving of the light reaching film or paper. One stop more light is twice as much, and one stop less is half.

Shutter speed, aperture, film speed and enlarger exposure are all measured in stops. It has nothing to do with stop bath, the chemical that halts development.

Stabiliser

The last bath in the C-41 colour process. It protects the colour dyes from fading and helps the film dry without marks. Do not rinse after it.

Stop bath

An acidic bath (often a weak acetic or citric acid solution) that immediately halts development and stabilises pH before fixing. Using a stop bath increases process consistency and extends fixer life.

Shutter curtain

A moving component in focal-plane shutter cameras that controls the exposure time by covering and uncovering the film. Shutter curtains typically operate in two main types:

• Cloth shutter curtain: often found in classic rangefinder and SLR cameras. It travels horizontally across the film plane.
• Metal shutter curtain: common in more modern cameras, typically moving vertically for faster shutter speeds.

The shutter curtain mechanism consists of a first curtain that opens to expose the film and a second curtain that closes to end the exposure. The gap between the curtains determines the effective shutter speed.

Shutter speed

How long the shutter stays open, and so how long light falls on the film. The dial usually shows the denominator on its own, so 125 means one 125th of a second.

Each step along the dial halves or doubles the light, the same as a whole stop of aperture. Shutter speed also decides how movement is recorded. A fast speed such as 1/500 freezes a running subject, and a slow one such as 1/15 lets it blur.

On a focal-plane camera the speed is set by the gap between the two shutter curtains. B, marked bulb on some cameras, holds the shutter open for as long as you hold the release down.

Silver halide crystals

Light-sensitive compounds used in photographic emulsions. When exposed to light, silver halide crystals undergo a chemical change that forms the latent image, which is later developed into a visible photograph. Common types include silver bromide, silver chloride, and silver iodide, each contributing to the sensitivity and tonal characteristics of the film or photographic paper.

SLR camera

A Single-Lens Reflex (SLR) camera uses a mirror and prism to show you the scene through the taking lens itself. What you see in the viewfinder is what the film will record. This provides an accurate representation of framing, focus, and depth of field.

Key characteristics of SLR cameras include:

• Interchangeable lenses: offering versatility for different types of photography.
• Optical viewfinder: uses a pentaprism or pentamirror to direct the image to the photographer's eye.
• Reflex mirror mechanism: flips up during exposure, allowing light to reach the film or sensor.

T

Test strip

A small piece of photographic paper exposed in steps at different times to determine the correct exposure for a print.

Take up spool

A cylindrical component in film cameras that winds the exposed film as it advances through the camera. The take-up spool keeps the film taut as it winds on, which is what stops frames overlapping. In some cameras it is a fixed part of the film advance mechanism. In others it is removable, or built into a detachable cartridge.

Temperature Coefficient

A measure of how temperature affects the rate of development. Higher temperatures accelerate chemical reactions, requiring shorter development times, while lower temperatures slow the process.

This relationship is usually specified as a temperature coefficient, defined as the multiple of the development speed for each 10°C temperature change. For example, a coefficient of 2.5 implies that the development proceeds 2.5 times faster at 30°C than at 20°C.

TLR camera

A twin-lens reflex camera has two matched lenses, one above the other. You look down at a screen that shows the picture from the top lens, and the bottom lens takes the photograph.

Most TLRs use 120 film. Well-known examples are the Rolleiflex and the Yashica Mat-124G.

U

V

W

Wash aid

A bath, also called hypo clearing agent, that turns fixer left in fibre-based paper into compounds that wash out quickly. It shortens a fibre print's wash from about an hour to about 20 minutes.

Wetting agent

A few drops of a detergent-like liquid, such as Ilford Ilfotol or Kodak Photo-Flo, added to the final rinse. It helps water run off the film evenly, so it dries without spots.

X

Y

Z