Medium format - focus on better definition

In his book Collecting and Using Classic Cameras Ivor Matanle, who is Britains best known and most respected authority on the subject, states: cameras with front-cell lens focusing, even high-quality Zeiss cameras, were rarely set to a true infinity focus even when fresh from the factory, and having the infinity focus set accurately is likely greatly to improve image sharpness.
That advice is repeated later in the book when he states that the Novar lens can produce first-class results if the focus is correctly set, and yields results indistinguishable from those of the more expensive Tessar in photographs taken in the middle aperture range, between f/8 and f/16.
Over a life of 50 years or more, many folding cameras will have been in for service or repair, and one might assume that the repair technician would set the lens to true infinity on completion of the work. No doubt many did, but the easiest, quickest and seemingly most accurate course is to return the lens to factory setting. However, as Mr Matanle states, the factory setting may have been inaccurate to start with.
How do we ascertain whether a lens is set to true infinity focus, bearing in mind that the movement of the front cell, which has to cover a range from infinity to 3 feet or 1 metre, is very small and that if it is wrong at infinity it will be wrong at the other settings?
The usual course for the amateur is to place a piece of ground glass in the film plane, set the lens to its maximum aperture and, with the shutter set to B, use a strong magnifier to check the image of a distant object on the ground glass. In most cases that works very well, but much depends on the amount of pressure exerted by the pressure plate on the film, and we must also take into account the fact that modern film bases are much thinner than they were when folding cameras were being made. In many cases the same applies to the backing paper. The net result is that the film may bow very slightly at the film plane.
Fortunately there is a way in which we can check and set the focus, and it involves no more than the expenditure of an hour or two and the cost of a film. The procedure is as follows.
Load the camera with a medium speed film, about 100 ISO and place it on a tripod. Make sure that the bellows are fully extended that the struts are properly set. With the lens set to infinity and stopped down to about f/8 for a lens with a maximum aperture of f/4.5 or f/5.6 for one with a maximum of f/3.5, take a photograph of a distant object. I find that an electricity pylon with many struts and cross braces is ideal. Now set the lens to the next setting, which may be the red dot or a distance of perhaps 12 metres or 30 feet and take a second shot. Make careful notes as you go of film frame number and distance setting.
Now place the camera, still on the tripod, at precisely 10 feet or 3 metres - a setting which is found on almost all medium format folders, but if yours does not have such a setting use the next nearest - from a flat target pinned to a fence or wall in flat lighting. . A sheet of newspaper containing small print, reverse print and various sizes of headlines is ideal. Do not guess the distance; use a tape measure. I use the centre of the bellows as the reference point.
Take a photograph of the target with the lens set at 10 feet and take further shots with the lens set to other distances - say, 8 feet, 7 feet, 5 feet and at two or three other settings, perhaps even between the marked distances on the focusing ring. It is vital to make careful notes of each and every exposure and distance setting. Now develop the film.
If possible, place the negatives in an enlarger and project an image on the baseboard of about 15 inches x 15 inches. If you have a focusing magnifier, examine the image from each negative and determine which is the sharpest. In the absence of an enlarger, examine the negatives with the strongest lupe - at least 5X and preferably 10X - that you can find.
If, for example, the sharpest negative of the set taken at 10 feet was with the lens set to 8 feet, we proceed as follows. Set the focusing ring to 8 feet. Using a very small screwdriver, slacken the three tiny grubscrews that are located around the rim of the focusing ring. One of them may be in an awkward position so turn the ring so that it is accessible and loosen it first. Then reset the ring to the 8 ft distance and loosen the other two screws; there is no need to remove them.
Without disturbing the lens itself, turn the focusing ring carefully until the 10 ft setting is at the focusing mark. Retighten the screws, but do not overdo it. A firm hold is enough. You may have to tighten two of them and then turn the focusing ring to gain access to the third, but the two screws will hold the ring while you do that.
What we have done is to place the 10ft setting at what was previously 8 ft. The negatives taken at infinity should also be checked and, if the example given is correct, the infinity shot at the 30 ft setting or the red dot will be the sharper of the two.
The instructions for carrying out the focusing test may seem complex, but once you embark on the exercise its principles become clear. I have used this method to check the focus on many folding cameras and in almost every case the definition was immensely improved. Having adjusted the focusing scale on your camera, you may wish to repeat the exercise to check the new settings and see the improvement.