For example, for Ilford Delta 100 I see listed development times for 50, 100 and 200, such as in this chart.

Are they referring to over and under developing times for the film? i.e. to develop normally (100), develop for 6 minutes. To under develop by a stop (50), develop for 4.5 minutes.


2 Answers 2


That's exactly what it means.

Delta 100 is an ISO 100 film, so if shot correctly and developed with Ilfosol S, the correct development time is six minutes.

If you'd overexposed the film by metering for ISO 50, you can't leave it in the developer as long, and they recommend 4.5 minutes with the same developer. This is called pull processing. (This is not something Ilford or most manufacturers recommend but is handy if you didn't set the camera properly.)

You can also push process film that was underexposed, which you'd do if you metered for ISO 200. Ilford doesn't have a recommendation for Ilfosol S, but if they did, it would be a longer time to allow more of the emulsion to react with the developer. If you look up at the Ilfotec DD-X row, you'll see that they recommend 14 minutes vs. 12 for normal development.

The blank boxes in the chart are combinations that either weren't tried or aren't recommended. (Probably the former.)

  • 1
    \$\begingroup\$ I would add that push/pull processing is a way of controlling contrast in an image. Large format photographers use this all the time to create 'ideal' printable negatives from subjects that are lit in different ways. Low contrast subjects often benefit from under exposure/longer development, and high contrast subjects can benefit from over exposure/shorter development. \$\endgroup\$
    – BobT
    Jan 9, 2017 at 3:42
  • \$\begingroup\$ If i may I would like to clarify that when Birfi says " meter for ISO 50 or meter for ISO 200 what you are doing is, if you are shooting 100 ISO film ( per you example ) you set your ISO setting dial on your camera to 50 or 200 respectively. The camera then meters for the ISO you have set the dial to. MAKE SURE you mark the roll with the ISO you shot it at so you can develop it with the times on the chart. The chart times are really guidelines, once you use a film repeatedly for pushing or pulling you may find you need to adjust the times for optimal negative density. \$\endgroup\$
    – Alaska Man
    Mar 5, 2017 at 5:36

A lot of things happen when you immerse your film in a developer. Since the developer is primarily water, it wets the film. The emulsion consists of light sensitive salts of silver. These are imbedded in a binder (glue) made of gelatin. The water causes the gelation to swell. This action opens up the gelation structure which resembles a jumble of transparent spaghetti. The silver salts are imbedded between the strands.

Now that the structure is swollen, the developer is free to percolate within. The developer seeks only exposed salts of silver, and when these are met, it reduces them to metallic silver by liberating the halogen component (bromine – iodine – chlorine). The liberated halogens are dissolved into the water of the developer.

All this swelling, infusion and reaction take time. Fast films (higher ISO) contain more silver salts -- thus the process takes longer. Slow films with lowered ISO, develop more rapidly. Developer manufacturers test their solutions on various film emulsions and publish their findings in the form of a Time-Temperature table. The developing time is different for high speed films, because they contain much more of the light sensitive goodies.

We can push-process: This is adding developing time to force the film to perform with an ISO that is greater than intended. We can pull-process: This is reducing developing time to correct for an unintentionally over-exposed film.

Additionally we extend developing time to achieve results that upraise the natural contrast of the film (yield a harsher image). Conversely we reduce developing time to reduce contrast (flat image).


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