Formats and cameras: 135, 120, sheet film, half frame, and what each asks of you

Film comes in three shapes: a cassette, a roll with backing paper, and a sheet. Each needs a different camera, a different reel or holder, and a slightly different photographer. Pick the format first and the cameras sort themselves.

135

The 35 mm cassette gives 24 by 36 mm frames, 36 of them on a standard roll, and it is the format the world standardised on. Modern cassettes carry a DX code, a pattern of conductive squares that tells an automatic camera the speed; Ilford's Delta 3200, for instance, ships in DX-coded cassettes, in 120, and in 100-foot bulk rolls for people who load their own ². Bulk loading cuts the cost per roll, by how much depending on the stock and the cassettes, and teaches you more about the cassette than you wanted to know. The film is thin: Ilford coats HP5 Plus for 35 mm on 0.125 mm acetate ¹.

Half frame doubles the count. Stephen Dowling's report at Kosmo Foto on the 2024 Pentax 17 quotes Ricoh: "two 17mm x 24mm pictures are captured in a single 35mm-format frame", which makes 72 vertical frames on a 36-exposure roll, through a 25 mm f/3.5 lens equivalent to a 37 mm, zone-focused down to 0.25 m, with a shutter from 1/350 to 4 seconds plus bulb and two stops of compensation either way ³. It is, as Dowling's headline says, the first Pentax film camera in twenty years ³, and the format's appeal is exactly the one the camera leans into: cheap frames, diptychs, a slower drain on the wallet.

120 and 220

A 120 roll is film taped to a strip of backing paper along its whole length, which is what lets you load it in daylight and, on older cameras, read the frame numbers through a red window. The same roll gives a different count depending on the camera: a 6x6 camera makes twelve square frames, a 6x4.5 fifteen or sixteen, a 6x7 ten, a 6x9 eight, the counts every medium-format manual prints. Ilford's 120 is on clear acetate with an anti-halation backing ¹; 220 was the same film twice as long, with paper only as a leader and trailer, so it needs a camera or back made for it and cannot be counted through a red window.

Kodak's developer sheets keep a unit that explains the economics: 80 square inches of film is one 135-36 roll, one 120 roll, four 4x5 sheets or one 8x10 sheet, and a 220 roll is 160 ⁵. A developer's capacity is quoted in those units, so a 120 roll, a 35 mm roll and a single 8x10 sheet each count the same against it.

Sheet film

Large format is film in single sheets, 4x5 inches and up, loaded one at a time into holders in the dark. Kodak's Tri-X 320 for sheets is coated on a 7-mil Estar thick base and can be retouched on either side ⁴; Ilford coats HP5 Plus sheets on 0.180 mm polyester ¹. Each sheet has notches cut in one corner, and Ilford publishes a chart of them ⁶: the pattern identifies the film, and its position tells your fingers, in total darkness, which side is the emulsion. A 4x5 negative has between thirteen and fifteen times the area of a 24 x 36 mm frame, depending on whether you count the holder's usable opening or the nominal sheet, and it is where developing each exposure to its own scene is simplest; see metering and the Zone System.

Which camera

A rangefinder focuses with a double image in the finder; it is quiet, small, and shows you the world outside the frame. A single-lens reflex shows you through the lens, usually wide open, with the taking aperture's depth of field only when you press a preview control, at the cost of a mirror that moves. A twin-lens reflex looks down into a square ground glass, which slows you down in the best way. A point-and-shoot decides for you; a folding camera from the 1950s fits a coat pocket and, in some 120 versions, makes 6x9 negatives, so check the model's format; a pinhole has no lens at all and lives on the reciprocity tables. A leaf shutter in the lens syncs with flash at every speed; a focal-plane shutter in the body syncs only up to a modest speed printed near the dial, which matters the day you buy a flash.

Start here

A manual 35 mm SLR with a 50 mm lens, from any of the big names, bought from a shop that tested it and its meter, is a good first camera: 35 mm is the easiest format to buy, load and develop, and a working meter can be checked against Sunny 16. Medium format is the step to take when you want bigger negatives and a slower pace; a rangefinder, when you want quiet and small. A folder someone's grandfather owned comes when you can service a shutter, or know someone who can.