A technique for preventing unintended actions by requiring verification of the actions before they are performed.Universal principles of design, William lidwell, Kritina holden and jill butler
We have all make mistakes in this game of film photography; set the wrong ISO, accidentally tripped the shutter, messed up the exposure or possibly even dropped a camera. Some errors are beyond the control of manufacturers to account for. Dropping is definitely one of them!
However, since the very beginning of 35mm film photography, designers and manufacturers have been thinking about ways to save us from our unintentional actions. This technique is a universal design principle called confirmation. You will most often see confirmation applied today in the virtual world of computer software and web applications in the form of the dialog box. The dialog box is a great error prevention mechanism, stopping you from unintended deletions of photographs on your SD card, sending emails without subject lines and leaving draft blog posts without saving changes.
A two-step operation
However, the principle of confirmation isn’t limited to the world of software. In the physical world confirmation usually takes the form of a two-step operation to perform a task, usually as part of critical or irreversible operation such as launching weapons or opening floodgates.
Making an exposure is far less critical than unleashing explosives and large quantities of water, but in the heyday of film professional wedding photographers, for instance, didn’t want their ISO dial freewheeling around or a twitchy trigger finger wasting valuable film.
Shutter release lock
The shutter release lock and the lift and twist action of an ISO dial are both examples of the principle of confirmation. My Praktica FX2 has a rarer form of confirmation which disappeared when camera makers worked out to allow users to select from the full range of fast and slow shutter speeds available without having to switch from one set to another.
Lift and twist
The FX2 has a lift and twist mechanism over the shutter speed dial which allows the user to choose between a range of fast or slow shutter speeds. In perhaps an overkill of confirmation, selecting a specific shutter speed within either range is also done this way.
Later on, as film cameras became more sophisticated and automated, another level of confirmation was added to the shutter release; the half press of the shutter button to both acquire focus and confirm exposure parameters before triggering the shutter; sensibly though, no lock was employed at this stage to impede you making an exposure!
Examples of use and omission of Confirmation
1956: Pracktica FX2 detail showing lift and twist mechanisms for both shutter speed selection, and fast or slow shutter speed set selection.
The FX2 has no exposure meter and therefore an ISO dial is not essential, although having a double lock on shutter speed selection makes the camera slower to set for exposure.
1959: Asahi Pentax S2 detail with no shutter release lock and free moving shutter selection dial.
The S2 was the first Pentax SLR to amalgamate fast and slow shutter speeds onto one dial. The lack of a lock makes speed selection quicker.
1959: Asahi Pentax S2 detail with free moving ISO selection dial.
The S2 has no meter, so the ISO dial serves as a reminder to the photographer the speed of film they are using. However, if the dial is accidentally moved, and the photographer forgets the film speed, the reminder is useless.
1968: Konica Autoreflex T detail showing shutter release lock, lift and twist ISO dial and free moving shutter selection dial.
With a built in meter able to calculate a shutter priority exposure, ensuring the ISO is set and immovable is critical for a well-exposed image.