Push me, pull me?

Undoubtedly there’s an art to the processing of Super 8mm film. The terms ‘push’ and ‘pull’ take us to the dark side of such alchemy – a place where film does things it was perhaps never intended to do. When were heard that Australia’s Nano Lab were doing all sorts in this field we asked head honcho Richard Tuohy to explain a little more about this weird science…


Here at Nano Lab we do a lot of push and pull processing for our customers – primarily of the colour reversal Super 8mm film stocks.

So what exactly is ‘push’ or ‘pull’ processing I hear you ask? Simply put, its processing a film stock in such a way as it allows the film to be ‘rated’ at a different film speed (ASA) in the camera from that which straight processing would yield for that stock.

Super 8mm cartridges have a system of notches cut into the plastic that provide information to the camera as to the speed and colour temperature sensitivity (tungsten or daylight) of the film in the cartridge. These notches are ‘read’ by various pins or leavers inside the camera and many cameras were designed with only a few different varieties of film in mind. Most often the cameras with limited speed-reading capability were designed for just 40 and 160 ASA film. For people using these simpler cameras, we often ‘pull’ process their 64T Ektachrome film to 40 ASA. This gives correctly exposed results that look the same as if 64T was shot in a camera that can detect 64 ASA stock correctly.

It’s also possible to ‘push’ process film effectively giving the film a higher film speed – making it more sensitive to light – than it would otherwise have been. It must be noted, however, that push processing does dramatically increase the grain of the end result, as well as increasing the contrast of the image. Nonetheless, push processing can be just the ticket in a low light situation where no other option is available.

To prepare a Super 8 cartridge for push processing the speed notch on the cartridge has to be modified – specifically, made bigger – to indicate to the camera to rate the film at the desired higher ASA.

Comparison of notches, 160T on the left, 64T on the right

The most convenient speed increase of a 64T super 8 cartridge is to 160 ASA – an increase of 1 and 1/3rd stops of sensitivity. There are a few reasons we find that this is the best increase to go for. One is that when the Super 8 cartridge was first launched, the designers in their wisdom didn’t provide notch specifications for the full normal series of possible ASA speeds used in photography. Usually the series increases in 1/3rd stop increments. As it happens, the Super 8 designers skipped several of these, leaving us with an incomplete series that skips 125 ASA. Thus, there is no notch specification for the more obvious 1 stop push of 64T Ektachrome. Another reason is that a push of 1 and 1/3rd stops makes 64T effectively 160 ASA – and virtually every super 8 camera ever made is able to detect this speed, making this a very useful ‘push’. We also find that pushing 64T beyond this amount gives unsatisfying and less predictable results.

To prepare Ektachrome 64T so that it will be rated as 160 ASA in the camera, the speed notch, which is the upper-most and largest of the 3 notches visible on front edge of the Super 8 cartridge, needs to be enlarged by 5mm (or, 0.2 inches if you must!). This increase in length needs to be on the lower edge of the existing notch, such that the notch length is being increased in the direction towards of the middle notch (the ‘cartridge centering’ notch). This can be done simply – by snipping the plastic at this point using a pair of wire cutters, a craft knife or even a pair of scissors. The unwanted bit of plastic is then just folded down and snapped off. Easy!

It should be noted that push processing a roll to increase its effective ASA is not the same as having a higher film speed stock available in the first place, and as with a higher speed film, an increase in grain is to be expected. But as stated above, pushing a film also increases its contrast – indeed, that is precisely how pushing works. Simply put, the contrast of a film (or more precisely a ‘film/developer combination’ as contrast is a product of the film combined with how it was developed) is the ratio between how much light is needed to barely register an image on the film, to how much light will fully expose the film. In a low contrast film, the difference between the two extremes will be larger than in a contrasty film. A low contrast film will record a greater range of light variations than a contrasty film.

So lets consider what happens in pushing. In a correctly exposed positive film image, a ‘highlight’ will be an area that is almost clear (white) or indeed, if quite small, completely clear (white). In an underexposed image, this area that should have been a highlight will instead come out dimmer (darker). By increasing the contrast through push processing, this ‘underexposed-highlight’ will once again become a highlight, but there will be a smaller range of light variations recorded on the film than would have been the case. This is most noticeable in the shadow areas of the film. Comparing a slower ASA film that has been pushed to a higher ASA with a film that genuinely has the higher ASA, the pushed roll will have less shadow detail, though the highlights will be the same - that is the basic difference.

Lucy the Nano Lab dog, pushed to 160 ASA on Ektachrome 64T

In practice, then, how does Ektachrome 64T pushed to 160 ASA compare with the old Ektachrome 160? When the 160 ASA Ektachrome was released in the nineteen seventies, Kodak advertised the stock with lots of low-light images of kids in the bath and rooms lit by candles etc. These were real low-light images: they were often shadowy and lacking in highlight … and quite amazing because there were images where nothing would have been recorded before. Pushing won’t work well in such extreme situations. However, where the E160 film was used in situations where a fully exposed image could result – i.e. result in an image with more than just shadowy information but a full range of light gradations all the way to a true highlight – Ektachrome 64T pushed to 160 will give quite comparable results.

Still from a client's Ektachrome 100D film pushed to 250 ASA

The other push option available with colour reversal super 8 film is pushing Ektachrome 100D. We find the same push - a push of 1 and 1/3rd stops to 250 ASA - very convenient. Once again, there is no 200 ASA notch, so it is not possible to prepare 100D for a single stop push (unless you are exposing manually that is). The same notch increase of 5mm is again all that is required to prepare the cartridge. This is off course an increase of 5mm from a cartridge that has been correctly notched as 100d… but this can’t be simply assumed.

A cartridge of 100D Ektachrome that has been notched for 100 ASA daylight film will have the same notching as a cartridge of Plus-X (7265). While there are several outlets for Ektachrome 100D in Super 8, I believe that few of these outlets currently notch their stock the same as Plus-X. Generally the companies that don’t notch Ektachrome 100d the same as Plus-X notch it as 64 ASA daylight – which is the same notch length as specified for 100 ASA tungsten. This is a notch 2.5mm shorter than Plus-x, so a modification of 7.5mm is required to rate the film as 250 ASA daylight.

Confused? Don’t be.

Still from a client's Ektachrome 100d film pushed 2 stops to 400 ASA

If in doubt, just consult a Super 8 notch specification chart like that found on the Kodak website or Wiki. Processed as 250 ASA, 100D Ektachrome exhibits grain similar to 64T Ektachrome when processed normally. The 100D Ektachrome can also yield good results when push processed 2 stops to 400 ASA.

Of course, to have your film push or pull processed, you have to find a lab that can do it for you. You need to ask the lab first to find out if they can, and if so, how much it will cost.

Don’t assume anything!

• For more on everything that Nano Lab, Australia's small film gauge specialists, can do - check out their website.
• To read Kodak's Super 8mm notch specifications - click here
• To download the Super 8 notch ruler from Wikipedia click here