One of today’s premium products is the cinematographic lens. It attaches to a digital still camera that’s being used in video mode, turning it into a cut-price cinema camera. These lenses have three attributes that distinguish them from run-of-the- mill lenses: a ‘clickless’ aperture control; calibration of that control in ‘t-stops’ as opposed to f-stops; and manual focus with a large rotation, often as much as 270°. Usually, the focus and aperture controls are fitted with gears, which can interface with a suitable ‘follow-focus’ unit.

Follow focus is something of a misnomer, as the gear does not ‘follow the focus’ – it simply allows a second person (other than the main photographer) to control the focus of the lens, for this is how cinematography typically happens. The camera operator is responsible for pointing the camera in the right direction and the ‘focus puller’ is responsible for making sure that the parts of the shot that should be in focus are in focus.

This is somewhat involved, since the focus puller has no view of the image being shot, nor even a viewfinder. In fact, focus pulling is done by measurement. Before the shot is taken, the distance from the camera to subject is measured, and the focus set by scale to that distance. This is the reason for the long focus scale, so that this operation can be carried out with sufficient precision.

If it is required to move the focus during a shot, then considerable skill is needed. The two positions – the start and end of the focus pull – will be marked on the focus control, and at precisely the right time in the shoot, usually synchronised with the camera operator panning the shot, the focus control must be moved smoothly and precisely from one point to the other.

Cine lenses used to be extremely expensive – which was mainly due to very low production volumes. The legendary British optical manufacturer Cooke (inventor of the Cooke triplet) still manufactures such lenses (visit www.cookeoptics.co.uk). Cooke is not vulgar enough to advertise its prices, but I found one of its dealers selling its 18mm T2.8 super 35mm lens (roughly APS-C coverage, equivalent to a 27mm lens on a full-frame still camera). It was priced at £5,650 – and this is from Cooke’s economy range. The Korean manufacturer Samyang’s 16mm T2.2 lens (roughly comparable with Cooke’s) costs just £330.

Doubtless, these lenses are very popular with filmmakers working on a budget, but this is a strange state of affairs. Given that purpose-made cinema cameras have been abandoned for still cameras, it seems odd that the traditional production practices of cinematography are maintained.

It’s a given that a serious filmmaker would eschew autofocus, since the visual effects of these systems catching and locking focus are not aesthetically the best, and attempts to follow focus (while effective) can be worse. However, a modern autofocus system does have the functionality needed to allow the focus puller to do his job, or even for the camera operator to do it himself.

The focus system measures the set focus distance, so it is entirely feasible to instruct it to set the lens focus to match a measured distance (although if focus is not to move during the shot, it would appear to be easier just to autofocus to the subject before the shot starts). Even the smooth focus pull can be achieved, not with any manufacturer’s native firmware, but using the Magic Lantern ‘hack’.

Bob Newman is currently Professor of Computer Science at the University of Wolverhampton. He has been working with the design and development of high-technology equipment for 35 years and two of his products have won innovation awards. Bob is also a camera nut and a keen amateur photographer.