Shutter-priority exposure

Konica was arguably the prime automatic-exposure innovator for interchangeable-lens SLRs. It was certainly the first SLR maker to produce a dependable, proprietary-mount-based automatic exposure system. It was a system of amazing simplicity and accuracy and it remained virtually unchanged for the duration of the system’s production – nearly a quarter-century.


"Unlike most SLR manufacturers, Konica didn't need to be dragged into the age of automation: We led it."

Konica Dealer Bulletin, July 1973

The market in general – and "serious" photographers in particular – were initially suspicious of the idea of automatic exposure. Received wisdom held that automatic exposure was the stuff of amateurs, that it was somehow incompatible with "real" or "pro" photography, and that it would produce a generation of "unthinking picture snappers". Konica, which seems to have had automatic exposure in mind before work even began on the AR mount (see Konica’s AR mount in this section), had been making automatic exposure SLRs for years when other OEMs makers recognized the benefits of automatic exposure. Of Konica’s five principal competitors:

Canon introduced its first AE SLR in November 1973, with the Canon EF (I am omitting the Canon EX, introduced in 1969 because it was not a true interchangeable-lens camera). It was a shutter-priority camera, but the automation was only available for the slower shutter speeds (1s-30s). It was also the only Canon SLR until 1983 to use a vertically-traveling metal shutter (made by Copal). The Canon AE-1, a shutter-priority camera introduced in 1976, was the first Canon SLR to offer automatic exposure through the entire range of shutter speeds. The first Canon SLR to offer aperture-priority automatic exposure was the A-1, introduced in 1978.
Minolta first introduced an automatic exposure SLR in 1973 with the Minolta X-1 (XK in North America, XM in Europe and the rest of the world), which was an aperture-priority body. The first Minolta SLR to offer shutter-priority automatic exposure was the XD (XD-11 in the USA and XD-7 in Europe and the rest of the world) in 1977.
Nikon’s first automatic exposure SLR, the Nikkormat EL, was
an aperture-priority camera introduced in 1972, using a Copal Square shutter. Nikon's first SLR to offer shutter-priority automatic exposure was the Nikon FA, introduced in 1983. Until then, Nikon relied on a quirky aperture-control servo attachment in order to provide shutter-priority AE in some models (Canon also made use of such an accessory on some models for many years).
Olympus’ first SLR with automatic exposure, introduced in 1975, was the Olympus OM-2, which was an aperture-priority camera. The Olympus OM-2S, a camera with a program mode released in 1984, was the company’s first (and only) SLR to offer something akin to shutter-priority exposure.
Pentax introduced its first automatic exposure SLR in 1971, with the Pentax ES, which had an aperture-priority system. But, not unlike the Canon EF, the automation on this camera was only available at shutter speeds slower than 1/60s. The company introduced its first truly automatic exposure SLR in 1975, the Pentax K2, also an aperture-priority camera. The company's first shutter-priority SLR was the Pentax Super A, introduced in 1983. 

Konica’s shutter-priority automatic exposure mechanism is referred to as a "trap-needle" system and is almost entirely mechanical. Simply put, it is a system in which the light meter’s needle is coupled, by means of a notched connector plate, to a stop-ring located behind the camera’s bayonet mount so that when the shutter release button is depressed halfway, the aperture indicator needle in the viewfinder and the connector plate are immobilized in a position determined by the amount of light read by the meter at a given ISO setting. Pressing the shutter release button further turns the stop ring as far as the notched connector plate will allow it to go. The stop ring has a protrusion against which the lens’ aperture actuating cam rests and the position of that protrusion determines the aperture used. Once all these elements are in place, pushing the shutter release button all the way fires the shutter. This basic approach to automatic exposure was emulated by a number of other SLR manufacturers, like Miranda, Mamiya, Petri and Ricoh.

It is the mechanical nature of Konica’s automatic exposure system that explains the extended travel of the shutter release button and the greater force necessary to depress it on Konica's early Autoreflexes. On most SLRs available at the time exposure had to be set manually and the shutter release button's only purpose was to trip the shutter. On some cameras, like many M42 SLRs, it additionally closed the aperture to the pre-selected position. On Konica’s early mechanical SLRs, this button serves to lock the exposure, immobilize the notched connector plate, rotate the stop-ring within the lens mount and, by so doing, close the aperture to the position determined by the light meter, and only then to trigger the shutter. All those elements – from the notched connector plate to the lens’ aperture mechanism – are spring loaded and the combined effect of several springs is the reason why depressing the shutter release button on Konica first SLRs requires more force than on other cameras.

Konica worked hard to reduce these drawbacks on its successive bodies and those efforts can be seen on the SLR bodies the company introduced between 1965 and 1973. On the Auto-Reflex, this button sticks out half an inch from the body. The shutter release button's spring tension and travel distance were reduced somewhat with the Autoreflex T, and even more so with the Autoreflex T2. The Autoreflex T3, however, is a camera on which the spring tension required by the shutter-priority AE system was decoupled from the shutter release mechanism and coupled instead to the shutter-cocking mechanism. On this and later mechanical Autoreflexes, the shutter release button's sole function is to lock the exposure and release the shutter. As a result, its travel was reduced to a tiny fraction of an inch. The force needed to depress it was reduced similarly.

The first automatic exposure SLRs were all shutter-priority cameras because such a system, by prioritizing shutter speed, acted on the aperture. All such a system was required to do was to determine the relative position of a number of elements, something that could be achieved using mostly mechanical means. The only non-mechanical part of such systems was the battery-powered light meter. The meter was needed to determine the position of only one element – the needle in the viewfinder. This position of the needle, once locked in place by slight pressure on the shutter release button, determined the position of all other mechanical elements in the chain that eventually led to the lens' aperture cam. In contrast, an AE system prioritizing the aperture acts on the shutter, which by definition means it has to control timing, as opposed to the relative position of mechanical parts. This was not attainable by solely mechanical means. It is only the advent of electronic timing-control technology in the middle 1960s that led to the appearance of electronic shutters (Pentacon in East Germany was the first maker to use one, in 1966) and to the first electronically controlled AE systems (Asahi Pentax was first with the Pentax ES, in 1971, followed by Nikon with the Nikkormat EL, in 1972). Until that time, and well beyond in many cases, unless one had a SLR equipped with an AE system similar to Konica’s, exposure had to be set by match needle.

One reason why some makers who would have liked to follow in Konica’s footsteps could not do so was the fact that their lens mounts would not support a mechanical shutter-priority system without extensive and costly redesign work. These constraints may help to explain those makers' ardent championship throughout the seventies of aperture-priority automation as the allegedly superior approach to photography. Ultimately, they also decided to offer shutter-priority exposure and, to enable this, their lens mounts underwent successive modifications throughout the seventies and eighties.

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The discussion above naturally brings us to one of the disputes most cherished by photographers – the old controversy about the alleged superiority of shutter-priority over aperture-priority, or vice versa. Users of shutter-priority point to the fact that the motion of the subject to be photographed – whether a running athlete, a bird in flight or a car driving past – is the factor which, more than any other, will determine the final quality of the image. Those who favor aperture-priority claim that depth-of-field is the most important factor, the speed of the moving subject being a secondary consideration.

As might be expected, I tend to side with the shutter-priority camp. As I see it, automatic exposure is the most useful – by definition – in situations when speed of operation is crucial. In photography, such situations involve movement. The quicker such movement is, the more useful the automatic exposure. Speed of operation in situations when there is simply no time to fiddle with exposure settings was the principal advantage of the early Autoreflexes over other SLRs. In such situations, a one or two-stop variation in shutter speed will have a much greater impact on whether an image is technically acceptable or not than a variation of one or two-stops in aperture value. To bring this point home, in some of its ads Konica in the 1970s lauded its shutter-priority automatic exposure system by stating that cameras that didn't have it (initially) and the aperture-priority systems of its competitors (later) were most likely to produce a "perfectly exposed blur".

That statement may sound a bit flippant, but it reflects real shooting conditions: No automatic exposure system can guess the speed of a moving object or the slowest speed at which a hand-held shot can be taken. Moreover, in most situations where depth-of-field is the primary concern – like portrait , architectural, landscape or macro photography – the photographer usually has all the time in the world to consider the aesthetic pros and cons of greater or lesser depth-of-field. In such situations automatic exposure itself is largely superfluous as there is plenty of time to set exposure parameters manually – something many champions of aperture-priority don’t seem to realize as they argue for the superiority of their approach. Given all the above, in situations when automatic exposure is most useful I feel a shutter-priority system will be more responsive and likelier to get the job done, so to speak, in a greater number of real life situations than an aperture-priority system. It seems to me closer to the essence of picture taking as a craft and as such, I prefer it.

Aperture-priority has two very important advantages over shutter-priority, however: It provides exposure automation irrespective of the type of lens used, whether manual, mirror or preset. It also doesn't require any coupling mechanisms or electric connections between the camera body and the lens, while shutter-priority automation depends on automatic lenses. In addition, an aperture-priority system allows for exposure automation during long, even several minute long, exposures. But, in my view, even this last advantage serves to emphasize how much better suited shutter-priority is for day-to-day picture taking. Unless one shoots architecture and landscapes from a tripod, or coins from a copy stand, photography usually involves movement of some sort. I feel that with shutter-priority, I will be better prepared.

In the end, Konica's competitors – most of which had initially looked down upon Konica's shutter-priority system as amateurish, and in time went on to tout aperture-priority as the "more desirable" or "superior approach" invested gigantic sums to provide shutter priority on their own cameras. Just how far attitudes had evolved by the mid-seventies can be seen in the fact that when the Canon AE-1 was introduced in 1976, its maker listed shutter-priority automatic exposure as the first of three features making the AE-1 the world's best selling 35mm SLR at the time. By the time the AE-1 PROGRAM was introduced in 1981, in its ads Canon extolled that camera's "shutter-priority sophistication".

Ultimately, one often comes to prefer a system for no other reason than because one has gotten used to it, and my views may be a case in point. Favoring one system over another is often little more than a preference for "what feels right" and, in the end, doing what feels right is always the sensible way to proceed in photography. De gustibus..., and the rest of it.