Wednesday, 24 April 2013

Rolleicord ‘waddling’ while focusing

There is often discussion in fora on what to do when the front of a Rolleicord or a Rolleiflex gets a bang, moving the lens and film planes out of parallel. An expensive repair is the answer. However, only rarely does discussion of another problem that can cause loss of parallelism arise.

In the 1980s, I had a Rolleicord Va with what I can only describe as a ‘waddling’ front end. When focusing, one side of the front end moved ahead of the other; eventually, the other side seemed to catch up when I stopped turning the wheel but I was never sure the lens became parallel to the film after being so far off. This is the only Rollei I have seen with the problem out of those I have had or handled. The mechanism that the front board runs in and out of the back part of the camera appeared to be loose.

Makers of bellows or other cameras with collapsible fronts used emphasise that their construction ensured the film and lens planes were parallel. But what is the margin of error in, say, that Rolleicord?

Using standard formulae for circle of confusion and for depth of focus (i.e. the distance from the film plane at which an image is in sharp focus or lens-to-film tolerance), the total depth of focus at f16 is 1.7 mm, for a Rolleicord/flex. However, depth of focus, like depth of field, decreases as the size of the aperture is increased. By f3.5 it is 0.37 mm and by f2.8 only 0.3 mm. So I probably would not have noticed anything wrong with my waddling Rolleicord at small apertures. But at f3.5 and focused at the centre of the screen, it would only take one side to be 0.15 mm further away and the other to be 0.15 mm nearer the lens for the effect of lack of parallelism to become apparent.

Also germane to this point, is the discussion of the flatness of film after being left in a camera for some time and the superiority of the film path of the Minolta Autocord over the Rolleis. Again, the effect would be more apparent at large apertures, and in the f2.8 Rolleiflexes in particular.

With folding 35 mm cameras the tolerance is even tighter. One of the last cameras my father bought for his collection before he died was an Agfa Karat 36 with a Rodenstock Heligon f2 lens. I remember that the struts of this great camera were particularly impressive in the way that they ensured film and lens planes remained parallel when the front was extended. They needed to be; at f2 the depth of focus is only 0.12 mm — the thickness of a sheet of printer paper.