Can a servo follow-focus add autofocus to manual-focus lenses on a Sony a6400?
Asked 9/29/2019
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I moved from a Canon EOS 7D to a Sony a6400 and noticed that native autofocus lenses are much more expensive than manual-focus or vintage lenses. I found a servo follow-focus accessory and wondered whether something like that could be connected to the camera so the body’s autofocus system could drive a manual-focus lens externally. In other words, is there any practical way to use the a6400’s AF with ordinary manual-focus lenses by adding a motorized follow-focus, or similar adapter/device?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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This looks like a video/cinema focus-puller's tool [albeit a budget one]
Even the good ones will not snap focus like a stills camera's AF. They are meant to be 'smooth' not 'fast'.
Even if you could access the camera's API [unlikely, as already mentioned by scottbb] then something this cheap will either refuse to keep up, burn itself out in half an hour, or will break either the gear teeth or the lens's mechanism if you tried to have it follow a stills camera's AF real-time.
Not really relevant to this, but a 'real' focus pulling kit will cost you about $£€ 8 - 10,000
...& you'd still have to calibrate it independently for every lens. Number of turns on the outside does not map linearly to distance focus travels, inside. The pro rigs have interchangeable collars you put on the driver remote to match focus distance of lens to position of dial on remote… and no matter how good the stereoscopic distancing systems mounted on high-end movie cameras, every focus-puller has a tape measure.
Originally by user57929. Source · Licensed CC BY-SA 4.0
user57929
6y ago
0
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In practice, no. A servo follow-focus is a video tool for smooth manual focus pulls, not a stills-camera autofocus system. Even if you could motorize the focus ring, current DSLR/mirrorless systems generally do not expose their autofocus sensors and control logic over USB in a way that would let an external device drive a manual lens like a native AF lens.
There are also mechanical problems: manual and vintage lenses have different focus throws and non-linear focus behavior, so any external motor would need lens-by-lens calibration. A budget follow-focus is also unlikely to be fast, precise, or durable enough to match modern AF behavior, and could damage gears or the lens if pushed too hard.
Some niche workarounds exist in other systems, such as focus-confirm/manual-focus assist features, or certain adapters with their own autofocus mechanisms, but these are not the same as turning a normal manual lens into a true autofocus lens via the camera body.
If you want AF on the a6400, native AF lenses are the practical route. Otherwise, use manual-focus aids like focus peaking and magnification.
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AI6y ago
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