Can a purely mechanical mirrorless lens adapter theoretically report the lens aperture to the camera?
Asked 12/4/2018
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Adapters for older manual-focus lenses (such as Minolta MD or Canon FD to Sony E or Fujifilm X) usually provide no electronic feedback, so the camera cannot display the selected aperture. In principle, could a mechanical adapter include sensors and electronics to detect the lens’s aperture-ring position and send equivalent aperture information to the camera? Or do mirrorless camera mounts generally lack any way to accept aperture data unless it comes from a native electronic lens?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
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It is certainly theoretically possible, at least with the mechanical designs of some older lens mounts, particularly with the relatively large amount of space afforded by adapting lenses with 40+ millimeter registration distances to cameras with 20mm or less registration distances.
The most likely reason we haven't seen any¹ is that there is no real market demand for such a device. I can think of several factors that might be in play:
- Using older manual focus lens mounts means the user is already giving up autofocus. This usually also means they're using such lenses is a way that allows plenty of time to set up a shot. (No one is using adapted manual focus lenses to shoot sports action for hire.)
- Most of those shooters comfortable with focusing manually are also comfortable setting exposure manually. They're happy to use either an external light meter, or to dial in exposure by taking test shots and using the histogram to adjust for the next shot.
- One of the main motivations for using older lenses on newer cameras is to lower costs as much as possible. Lenses in older, pre-AF mounts tend to be cheap and plentiful. Simple mechanical adapters are cheaper than would be the case for complex mechanical adapters that would measure a mechanical position of a pin/lever and translate that to an electrical communication to the camera body.
¹ For all I know, such a thing may actually exist somewhere. But if they do, they're not widespread or well known.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
7y ago
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Yes—at least in theory, an adapter could sense the position of a mechanically coupled aperture ring or lever and translate that into electronic data for the camera. The short flange distance of mirrorless bodies often leaves enough physical room in the adapter for such hardware.
The main reason these adapters are rare is probably practicality, not impossibility. People using old manual-focus lenses have already accepted manual focus and manual or aperture-priority shooting, so there is limited demand for extra complexity just to display the selected f-stop. It would add cost, calibration issues, and mount-specific engineering.
Also, the adapter would only know a mechanical position, not necessarily the true effective aperture with complete accuracy across different lenses unless it were carefully designed for that lens family. So while it’s theoretically possible on some mounts, it has not been worth building for most users or manufacturers.
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