Throughout the history (to date) of photographic lenses, there have been a number of different way to arrange the aperture (adjustable-size opening) of photographic lenses. These alternatives are briefly described here:
None
Some lenses do not have adjustable apertures at all. Some typical examples of this type of lens are projection lenses, but in early history, also photographic lenses were produced without an affordance to change the aperture.
Masks
Some lenses have used/use slot-in/drop-in aperture masks that are inserted inside or on top of existing objectives. Aperture masks open the door to using openings that are everything but circular, including quadratic masks, star-shapes, etc. Many very early lenses used aperture masks as do some modern specialty lenses.
Manual
Manual aperture lenses typically sport a multi-blade aperture mechanism that is directly controlled by the photographer manipulating a control on the lens (dominantly that control is a ring). Most often manual aperture lenses do not have click stops (are clickless) but there are exceptions.
Example: Jupiter -8 for Leica thread mount
Preset:
Preset typically have two rings for controlling aperture: One ring to set the smallest allowable value (the intended shooting value) for a lens; another ring to manually control the aperture size between maximum size and the preset value. Predominantly preset lenses combine a manual, clickless aperture control ring with another ring (with click stops) that was used for setting the preset aperture. Preset lenses were intended to make the photographer’s life easier by allowing the photographer to 1) measure light and set the aperture preset according to that measurement; 2) lift the viewfinder to the eye, focus and frame wide open; 3) quickly twist the aperture ring to the preset value and press the shutter release.
Example: Meyer-Optik Görlitz Orestor 135 f/2.8
Semi-automatic
A semi-automatic aperture typically meant that the aperture would stop down automatically (i.e. when commanded by the camera) to the selected aperture, but a photographer’s actions would be needed to open up the lens again. In practice, most semi-automatic lenses were (in terms of usability) preset lenses where simply the act of stopping down the aperture was automated.
Example: Carl Zeiss Jena Biotar 58 mm f/2 for Praktina
Automatic
Automatic aperture means that the lens remains wide open until it is automatically stopped down to the selected aperture when the shutter release is pressed, and after the picture is taken, the lens opens back up again.
In practical (mechanical) terms there were two ways in which this could be facilitated: Lenses could either be designed according the ‘release to stop-down’ or ‘actuate to stop-down’ logic
A ‘release to stop-down lens’ would have a spring that would consistently try to pull the aperture to close to the value set by the aperture ring, but when mounted on a camera the camera would push/pull a pin or lever to keep the aperture open until at he time to shutter release was activated. At that time, the body would ‘release’ the lens, allowing the lens to stop down. Examples: Nikon F, Minolta SR
An ‘actuate to stop-down’ lens would instead have a weak spring that would constantly try to pull the aperture as open as possible. Instead, when mounted on a camera, the body would need to overcome that spring in order to push (actuate) the pin or lever to such an extent that the lens would stop down to the pre-selected value. Examples: M42 (automatic), Olympus OM
In terms of actual use, both approaches have distinct advantages and disadvantages.
Electronic
Electronic means that the lens’ aperture mechanism is actuated solely through an electronic impulse (no mechanical pins or levers). Besides most mirrorless lens mounts, the Canon EF mount is a promiment adherent of the Electronic approach
Impacts on adapting
In terms of adapting, the less elaborate the aperture mechanism, the more easily it can be adapted (as long as the lens has a functional aperture ring).
Manual and preset apertures are very easy to adapt, as are ‘release to stop-down’ automatic aperture lenses. In the case of ‘actuate to stop-down’ lenses, the adapter needs to facilitate that actuation, either through an immovable flange or pin (M42 and Olympus OM adapters) while in some cases facilitating aperture operation will furthermore necessitate an adapter with control ring (e.g. Fujica X mount)
In the case of electronic apertures, stopping down the lens will necessitate a smart adapter that is able to communicate (and often translate) the electronic inputs from the camera body’s electronic contacts to those of the lens’ electronic contacts.
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