Most of us will send our exposed film to normal processing, reversal film for E6, color negative film for C41 and b&w negative film for b&w film processing. However, there are extra modification or alternate process technique which you can use to change the look of your film.
I will cover the following three special film processes this and the next two posts:
- Push/Pull Processing
- Cross Processing
- Silver Retention/Bleach Bypass
Although the impact of using an alternate processes will vary, in most cases, it effects changes occurring in color emulsions, which may not be occurring equally in all layers. These changes are:
- Improper color reproduction
- Speed shifts
- Contrast changes
- Increased fog
- Increased grain
Push/pull processing is commonly used when the film is accidentally or intentionally under-/over-exposed. Unlike digital camera, the ISO of film cannot be changed and you have to decide what ISO of film will be needed for your shooting before loading the film into the camera. However, we may not have the right ISO film on hand when shooting so push/pull processing is a counter measure to change the film’s ISO.
Push processing is overdeveloping to simulate increased film speed. Push processing began with B&W films and spread to color films. It was used in the past to produce a normal density negative from an underexposure. The lab will compensate for this in the first developer in a reversal process or the developer in a negative process, and the result is often a grainy or gritty ‘look’.
The developer solution is the only stage of the process that does NOT go to completion. We control the extent of the development by carefully controlling the time, chemistry and temperature of the developer solution.
Push processing effectively overdevelops the negative by increasing the development time. That way, the silver develops more than normal.
It is termed as either a 1 stop or a 2 stop push, which is related to the amount of underexposure applied to the negative.
In push processing, some of the silver halide grains that were not exposed are forced to develop up. This occurs more in the toe where shadow detail is lost. The image that results appears too grainy.
Pictorially push processing will result in:
- Higher contrast
- Color imbalance, curves are not parallel. There is some movement in the RGB layers that is not consistent. A color imbalance is likely in the shadows or highlights.
- More grain – As we fog or process up the Dmin to a higher density, more grain is evident. This is a technique that some photographers like.
- Smoky blue shadows – Because of changes to the yellow record, shadows will go smoky in appearance and sometimes actually appear blue.
This graph shows the effect of push-1 processing on a color negative film. The dotted line is the reference and the straight line shows the sensitometric change that occurs when the film is push processed.
These curves show the effect of over-development. There is more development in the toe, particularly in the blue record, and it continues up the sensitometric curve. The blue record is most sensitive to push processing than the red or green layers because it is the top layer in the film structure. There is also an increase in red and green contrasts as a result of the greater increase in density in the higher exposure range than in the lower scale.
This graph shows the effect of push-2 processing on a color negative film. The dotted line is the reference and the straight line shows the sensitometric change that occurs when the film is push processed.
Here the effect is more dramatic. The yellow layer is much more over-developed, particularly in the toe. It is more than double the effect of the push-1 process shown on the previous slide. Also, looking at the blue curve, notice that the entire curve is “shifted” higher – including the Dmin. If you consider that “scene content” should all fall within the straight line portion of the curve, you really have not gained any “speed” with the push process. For example, take an exposure at –2.50, the density with the push process is about 0.40 heavier than the normal process, but its position on the curve is still relatively the same. In other words, there is still only about .50 Log H underexposure from that point before you are into the Dmin of the film.
Pull processing is less common than push processing. In this case, the negative is under-developed. As with push processing, this is often done in combination, that is, overexposing the negative and then under-developing it to achieve a normal negative density.
This graph shows the effect of pull-2 processing on a color negative film. The dotted line is the reference and the straight line shows the sensitometric change that occurs when the film is pull processed. In pull processing, the D-mins of the film drop a little bit, but the major effect happens in the higher density areas. The contrast is actually lowered.
It is highly recommended that you talk to your processing lab about push/pull processing and conduct some tests to make sure you know its effect before you use this technique to shoot an important scene.