Sunday, 30 June 2013

Lens Depth of Field Scales. 1. Hyperfocal Focusing and Circles of Confusion

I know it is difficult to incorporate depth-of-field scales in modern zooms but even on modern prime lenses (like my Nikon f1.4 50 mm) they are rudimentary to the point of uselessness). And I miss them. One of the great advantages of a proper depth-of field-scale is the rapid setting of the hyperfocal distance without having to remember what the hyperfocal distance is. All you have to do — and it seems that very few photographers know this — is decide what the near point of acceptable focus is (by focusing on that point and reading the focus scale), swing the focus ring so that the ∞ mark lines up with a particular aperture (e.g. f/8) on the depth-of-field scale, then look at the other side of the scale to see if at that aperture the near point shown on the focus ring is within the range of acceptable focus. If it is, then set that aperture for exposure. If it is not then move the ∞ mark to larger aperture number (i.e. smaller stop, e.g. f/11) and try again until the near point is within the range. The whole process is so rapid that it is easier to do than describe.

These photographs of the focus ring and depth-of-field scales of an f/2 50 mm Pancolar lens illustrate the point. In each case the ∞ mark on the focusing ring is swung to the point indicated by the aperture (f/8 in one photograph, f/11 in the other). It can then be seen easily that the range of acceptable focus is from about 12 feet (about 3.5 metres) to infinity at f/8. The focus mark is at the hyperfocal distance but you didn’t need to remember that or look it up in tables or even in a depth-of-field app to get there.

Similarly, in the second photograph, using f/11, the depth-of-field extends from about 8 feet or 2.5 metes to ∞.

Here, the aperture is f/8 (lower ring). the focus (upper ring) is swung so that
the ∞ mark is opposite f/8 on the depth-of-field scale (middle). The point of
acceptable near focus can be read from the focusing ring at the f/8 mark on
the depth-of-field scale. The point of focus (orange arrow) is at the
hyperfocal distance.

Same as above, this time using f/11

Now, the interesting point is that you will not get the same result using a modern depth-of-field calculator for a full-frame 35 mm lens. Instead of 12’ to ∞ at f/8 we get 17’ to ∞, and instead of 8’ to ∞ at f/11 we see 12’ to ∞ on a calculator. The explanation is simple. The depth-of-field scale markings on an individual lens depend on the value taken for the circle of confusion used by different manufacturers at different times. For the Pancolar made by Carl Zeiss Jena in the 1960s shown in the illustrations above, the circle of confusion was taken as 1/20 mm (i.e. 0.05 mm). This is what Werner Wurst had to say in the 9th edition of his Exakta Manual (2nd English edition, 1966):

...a circle of confusion of 1/20 mm is still recognized as sharp for the 24 x 36 mm format. The tolerances of unsharpness in which the depth of field scales of the EXAKTA Varex lenses made in Jena and Görlitz are based are derived from these data. However, other optical manufacturers reject as unsharp anything larger than 1/25 mm [0.04 mm]. In actual practice these variations can be ignored; however, bigger variations in either direction can no longer be tolerated. Thus, the assumption of a still smaller circle of confusion (e.g. 1/30 mm [0.03 mm] would unduly restrict our possibilities during focusing while larger diameters (e.g. 1/10 mm [0.1 mm] will be immediately be recognised as unsharpness.

It is interesting that the current practice is to use 0.03 mm for the full-frame (24 x 36 mm) format. Thus, depth-of-field is taken to be shallower than was once regarded as perfectly acceptable by a major lens manufacturer. Whether we can discern a difference is another matter.

What we can do is to compare the reading for near acceptable focus and hyperfocal distance obtained with a depth-of-field scale on an old lens with those values calculated using an iPhone app and the like. By using different circles of confusion in the calculation, it is easy to determine what value was being used by a particular lens/camera maker at the time of manufacture. You can then decide — provided you are using the lens with a sensor of the same format for which it was designed — whether to stick with the depth-of-field scale on the lens or move to a smaller circle of confusion and a shallower calculated depth of field.

Thursday, 20 June 2013

Ilford Advocate: Why Ivory?

The article on the Ilford/Kennedy Instruments Monobar camera in Amateur Photographer earlier in the year reminded me of a question that had niggled me for years. Why was the body of the Ilford Advocate ivory in colour?

In its day the Advocate was not a popular purchase or seen by most amateur photographers in Britain as an object of desire. In the early 1950s it could be seen in chemists’ shop windows (pharmacies) amongst the display of Ilford film. But the objects of desire were not this British-designed and built 35 mm but German black leatherette and chrome, even when imports of the latter were restricted to cheap models in the aftermath of the war and protection of the £ sterling currency.

The Advocate was relatively expensive and the colour really did put people off. Serious cameras were black — full stop. Somewhere Ilford marketing had failed. The bright, sunny Ilford displays with their bright white (well ivory) camera had not worked and the cameras were eventually sold off at sale prices.

I read in the AP article that the Advocate was designed and built by Kennedy Instruments. A good deal of laboratory equipment in the 1950s and 1960s was stove-enamelled in ivory. Therefore, I wondered if Kennedy Instruments were scientific instrument makers who then manufactured the Advocate. To satisfy my curiosity I bought the book, Faces, People and Places. The Cameras of Ilford Ltd 1899-2005, by Andrew Holliman from the author*. It appears that Kennedy Instruments (partly from 1949 and then totally owned by Ilford) were not instrument makers in the laboratory sense but came from automative engineering to camera design and construction (including cameras for the Keartons in the 1930s and for aerial reconnaissance).

The ivory finish of the body was, it appears, chosen deliberately. Holliman writes:
   The most distinctive feature of the Ilford Advocate, especially against other cameras in any collection, is the ivory enamel finish. However, other colours were considered. Various methods mostly of different paint finish were assessed in an attempt to give the camera a black and chrome appearance but they came to nothing.
   At one time several bodies were produced in six different enamel colours, Red, Green, Blue, Brown, Yellow and Black, and presented to the Ilford Board for consideration. These were rejected by the board.
Holliman also describes the problems Kennedy Instruments had in trying to get lenses in sufficient quantities from British manufacturers. Dallmeyer could supply with consistency and ‘quite high quality’ but not quantity. Wray had problems with quality control leading to many of their efforts being rejected. Ross also could not supply a suitable lens. The price of the Advocate remained high because economies of scale could not be achieved.

The high prices achieved for these cameras in sales, even of wrecks on eBay, to present-day collectors is a result of marketing and manufacturing failure. Successful cameras are not that rare.

By contrast, consider the later Ilford Sportsman, made in Germany by Dacora. I was surprised to learn that Ilford at one time held over 50% of the UK 35 mm market with the Sportsman series and that this level of sales is thought to have helped them (with the little stickers in the film compartment) to capture the major share of the 35 mm film market. The cost to Ilford of the original Sportsman was less than £3 which was less than the cost of the lens for the Advocate. Dacora were not at the premium end of the German manufacturers but for the British mass market of the 1960s a low headline price held (and sadly still holds) sway.

Finally, looking at the Ilford/Kennedy Monobar in Holliman’s book, I cannot help but think what a superb technical camera it would be with a 24 x 36 mm digital sensor instead of the film holder.

*Andrew Holliman’s book (ISBN 0-9655342-1-2) was published in 2006. It can be obtained from him through his website:

Tuesday, 11 June 2013

Exakta Varex Cameras 1: When New

I had an Exakta Varex IIb camera for twelve years. Bought in Hong Kong with a 50 mm f/2 Pancolar lens, it served me well enough but I had no qualms when the time came for a change to the Olympus OM series.

So why am returning to Exakta cameras now? I needed some exposed 35 mm black-and-white films for a project that will appear later this year. Instead of buying a relatively modern 35 mm SLR I thought it would be interesting to buy a few Exaktas to see how they have survived and use them to generate the exposed film. Before describing how I got on, I thought it worth describing what it was like to use a new Exakta Varex in the mid-1960s and then go on to describe the problems with trying to use the cameras now.

In its day, the Exakta was the 35 mm single-lens reflex camera. For many applications, it was far superior to the rangefinders such as the Leica or Zeiss Contax. I wanted a camera for close-up photography of small animals and the Exakta Varex was the desirable camera for such applications in the UK of the1950s and early 1960s.

Some of the irritations of using Exaktas had gone by the mid-1960s. For example, the newer lenses had automatic diaphragms, closing before exposure as the release was pressed. Such a change made the Varex IIa and IIb more suitable for the ‘normal’ sort of photography associated with non-reflex cameras.

Exakta Varex IIb with Tessar 50mm f/2.8 lens
Roger Hicks, in his excellent website*, describes the idiosyncrasies of the Varex IIa and of using the camera in the present day. Some of what we now regard as idiosyncrasies were the norm of the time, the non-return mirror for example. Other features made the Exakta system highly versatile.

Right handers find the Exakta Varex awkward to use. Even left handers like me find the shutter release strange. The shutter is released by pressing the button on the left hand side of the lens towards the camera body. With the later fully-automatic lenses the initial movement closes the diaphragm, then the movement reaches the shutter release on the body of the camera. An ear-piercing clunk accompanied by a squeal indicates the focal-plane shutter has done its job. Then, until the film is wound and the shutter cocked, the viewfinder is dark. There was, as I said above, no instant-return mirror. I found it difficult to hold the camera securely and press the shutter; I still find it difficult. I think the problem is that the axis of holding the camera firmly is at 90° to the release movement.

The external linkage between lens and body was a pain when using extension tubes. Auto-couple release rods with brackets which screw into the front of the lens and into the body release were made by Ihagee for use with extension tubes and bellows. If using them for hand-held photography the length of rod in use has to be adjusted so that the automatic diaphragm closes before the body release is triggered. The obvious answer is to use a double cable release but this solution was not in the Ihagee line up of equipment.

Showing the external coupling from lens to body release
Exakta Manual, Werner Wurst, Fountain Press, 1966

On fully automatic lenses, the diaphragm can be locked at the set aperture by pressing the release and turning the knurled ring under the release button. This procedure is needed for T and B exposures.

The lever wind is also in the left side of the body. This needs a complete all-in-one turn of 270°. I achieve the wind first by using the thumb to advance it half way and then the forefinger to reach the full distance.

Lever wind - left, at rest; right, near the end of its travel.
The shutter speed dial is also shown.

Changing shutter speeds is awkward. To avoid damage, the speed-setting dial is turned in one direction only. Therefore, when wanting to change from 1/250 to 1/500 (adjacent settings on the dial), the dial has to be turned nearly 360° while lifting it against a spring. A tiny red dot indicates the speed in use.

Using the slow speeds (longer than 1/30) often has newcomers fooled. The slow speeds start at ⅛ second on the Varex IIb and at ⅕ on the IIa. Therefore, the natural progression  of speeds between 1/30 and ⅛, i.e. 1/15 is missing. To set a slow speed, the normal shutter speed dial is set to T or B. Then the slow speed dial is wound up by turning it clockwise until it stops. The speed on the large dial is set (up to 12 seconds) using the black numbers. Finally, the release is pressed.

The large slow speed dial also serves to operate the delayed action release (self-timer). At speeds set on the normal speed dial, the slow dial is wound as before and then set to any red number. When the release is pressed there is a delay of 12 seconds.

For slow shutter speeds with delayed action, the procedure is to set the normal dial to T or B, wind the slow speed dial as above and then set the shutter speed using the red numbers. Doing all that lot really slows photography down but is only equally infuriating to the menu-driven procedures on too many modern cameras.

The slow speed/delayed action dial with film reminder
disc in centre

Rewinding the film can be a nail-breaking experience in the Varex IIb. When the rewind crank is unfolded, the rewind knob turns without engaging the rewinding. When it is extended, the rewind axle turns. However, as the crank is turned (while holding the film release button on the top of the camera) I find it slips out of gear leading to the film being rewound in fits and starts and the finger nails catching on the knurled and tiny crank handle. I supposed Ihagee changed that in the Varex IIb in order, theoretically, to speed up the rewinding process and therefore the changing over of films. In the IIa, the rewind knob is engaged by pressing the centre section such that prongs make contact with the cassette spool.

Varex IIb. Rewind crank in use (left) and closed (right)

Varex IIa. Rewind engaged (left). Disengaged (right)

A real idiosyncrasy of the Varex is the film cutting knife. This knife allows a short length of film to be cut and processed separately. Coupled with its presence is the ability to have a cassette instead of the standard open spool at the receiving end of the film gate. Using that system, short lengths of films can be exposed, cut, wound into the receiving cassette and removed from the camera in daylight. That was a brilliant system for checking exposure and composition with technically difficult subjects. However, I have yet to find an Exakta owner who has not bled as a result of catching a finger on the blade.

Film cutting knife in closed position - waiting to nick an unwary finger
Knife being pulled across the film plane
The back of the camera can be removed by pulling
out the pin
A key to the versatility of the Exakta system was the ability to change viewfinders and focusing screens. The reflex finder could be changed for a pentaprism very quickly (more quickly in the IIb than the IIa, the latter having a catch on the front of the camera). I had the version with the pentaprism and fresnel lens with split-image rangefinder. Some writers have questioned the accuracy and ease of use of the split-image rangefinder but I had no problems in using that screen.

Varex IIa. Release catch for the viewing system - not present on the IIb

Initially, I thought the bayonet lens mounting system fine. However, when I used the extension tubes and a heavy lens on the front I noticed a pronounced droop. When I asked my colleagues if they too could see the droop, one thought it resembled Concorde’s nose (then of major interest in British newspapers) while others thought I had taken it to the pub too often. Somewhere or everywhere in the bayonet connexions the tolerances were too great.

I had one of the later model Pancolar  50 mm f/2 lenses; this had the automatic depth of field indicators and the zebra markings across to the focusing scale. I found it, when new, to be a sharp lens of moderate contrast (compared with modern lenses). 

Early 50mm f/2 Carl Zeiss Jena Pancolar with
conventional depth-of-field scale
Later 50mm f/2 Pancolar with automatic depth-of-field indicators
changing position as the aperture is changed

By the mid-1960s there is now no doubt that Ihagee, like the rest of the German camera industry, east or west, was losing its way. Japanese camera manufactuerers were overtaking them rapidly and I soon realised that I had actually made the wrong choice. For the same money (prices in Hong Kong were one-third of those in U.K. at the time), I could have bought a Pentax SV with its huge range of accessories (and internal linkage) or a Nikkormat. They were the future; Exakta was the past.