Film (+) Pushing and (-) Pulling
Often confusing and easily overlooked, the option of changing the effective speed of film by altering the development is known in the trade as pushing or pulling. Whilst never an ideal solution it can provide traditional photographers with a means of either compensating for difficult light conditions or correcting a mistake in exposure.
A quick history...
In the days before mainstream colour photography film development was a black art: variations in dilution; agitation; time; temperature and of course chemical composition were, and still are, minutely adjusted to produce BW negatives that suited the particular style or whim of the photographer. Famously an early exponent of Kodak D23 BW developer would put the films into the developer and disappear out for lunch at his club before returning some hours later to retrieve his films.
BW photography, with its abstracted interpretation of our world, allows for such processing diversity but our perception of colour images is less flexible: we anticipate the sky will be a particular shade of blue, we all know what colour grass should be or how skin should appear. To avoid unnatural results in colour images a more systematic approach was needed in film production and processing than the patchwork of techniques previously used in BW production.
Kodak was the film giant that led the way and ( skipping a few decades of change ) produced the transparency film types and process we still use today. The other manufacturers fell into line with this processing standard known as E6. Why “E6”? No particular reason, though E is for Kodak Ektachrome and 6 for the number of chemical stages in development: it should really be E9 but the original name has stuck.
What is a normal process?
This standardisation means that every E6 film is developed in an identical way, no matter what the speed on the film label. Fuji Velvia 50asa is designed for the same development time as Kodak Ektachrome 400asa because the speed variation is built into the emulsion, not the subsequent process. A good transparency still beats a DSLR image in terms of colour rendition and detail but requires the photographer to control exposure carefully: an underexposed (dark) transparency can be rescued at the scanning stage but a overexposed one is not worth the trouble. Better to start with a good transparency and pushing ( or pulling ) the film process is an extra tool for the photographer to use.
Push processing transparency film will
- Lighten the image
- Slightly increase contrast
- Slightly increase apparent 'grain'
There are some practical restrictions to pushing the process
- carried out in increments eg. +1/3, +1/2, +1, +11/2, +2 etc ( this allows for meaningful adjustments )
- limited to +3 ( at +2 the change is quite marked but +3 will result in washed out blacks amongst other effects )
- films have their own characteristics: density will be reduced as expected but subtle changes in contrast and colour will differ between film types eg. Velvia 50 becomes overly contrasty if pushed more than +1.
We have been asked to push +1/6 which we can do, but the resultant change in density is accepted as being undetectable by eye.
When to use it
You might find yourself in a low light situation with a 100asa film, perhaps you forgot the tripod or have a moving subject that requires a faster shutter speed than conditions allow? Set the film speed on the camera to 200asa, shoot as though the film were labelled as such and then mark the film to be pushed +1 stop. If you decided to set the film to 300asa then the film would need to be pushed +11/2, 400asa then +2stops.
The same increments work for a 50asa film such as Velvia 50: set the camera to 100asa and instruct to push +1 stop; at 200asa instruct +2 stops and so on.
Well-practised photographers, who are familiar with the characteristics of their film, may intentionally change the exposure and development for effect: pushing a film +1/2 stop can add a little contrast and 'lift' to a dull light situation.
When not to use it!
When film is developed the entire film is immersed in one go, so it is not possible to change the development for the first 20 exposures: the whole film is altered. If you discover you have inadvertently set the wrong speed half way through a roll then continue at the 'wrong' speed and instruct the lab to make the necessary adjustment. If you are uncertain then write down the settings, pass them on to the lab and let them advise the best course of action.
However this will not help if the camera meter has been left set at 1600asa and you have 50asa film loaded: in theory that would mean an adjustment of +5 stops. If the film were pushed +5 stops the resulting film would be lightened so much the whole film would be almost clear, with no useful image at all. So if the meter setting is wildly out it will be better to correct the meter setting and repeat those incorrectly exposed photographs because they will be a write-off.
What about Pull processing?
There is less demand for pull processing, for good reason. The effect is to reduce contrast and colour saturation and to most photographers this not an attractive appearance - the colours begin to look 'muddy'. It is limited to -1 stop because to go beyond -1 will mean the development time is reduced so much that unwanted effects, such as uneven development, can start to appear.
Since it has the opposite effect to pushing, the effective adjustment would work like this: a 400asa film shot at 200asa would need -1 stop etc.
What about C41 Colour Negative film?
There is seldom a need to adjust C41 development because there is so much exposure latitude in the film and the subsequent printing. The manufacturers reluctantly accept that colour negative film can be pushed or pulled but do not recommend it, because the photographic results are unpredictable. The resulting prints might, for instance, have greenish shadows and pink highlights due to an image imbalance called 'crossed curves' that is very difficult to remove without careful adjustments in Photoshop.
Push processing is useful tool but one that requires care. Subtle improvements can be made to some images by pushing under 1 stop but beyond that we are looking at saving images that would be otherwise be too dark for use.
The Darkroom UK Ltd