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I recently switched from a EOS 7D to a Sony a6400 and since I have to buy new lenses I saw the huge difference in price between compatible AF and manual focus lenses. I also stumbled upon this: Zhiyun Servo focus

https://www.amazon.com/Servo-Follow-Focus-Mechanical-Panasonic/dp/B0794V7TF3

This got me wondering, since the processing for AF is done in the camera body and that this servo follow focus can act on the camera's follow focus, is there a known way to connect something like what I just linked to let's say the USB port of the camera to use the autofocus functions of the camera on ordinarily MF lenses?

That would essentially allow us to use high quality low cost Vintage lenses with the AF capabilities of modern Digital cameras!

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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.

  • Comment rather than part of the answer, as it's really off-topic. focus motor 4 grand for the 'mini', & remote controller 7 grand. – Tetsujin Sep 29 at 17:45
  • Yes it is a budget solution for video, though I am planning to use the AF on vintage lenses mostly for filming, and even then this product is just an example, I could jerryrig a high torque brushless motor. I could also manually calibrate each lens and create different profiles for different lenses. I'll try reverse engineering the E-Mount using arduinos and tricking the camera into thinking it's focusing a genuine lens – R3D34THR4Y Sep 30 at 11:19
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    If it's actually for video, why not employ a 1st AC. That's what they're paid for, focus-pulling ..& gear lugging, if you've only a 2-man camera crew, otherwise the 2nd or 3rd AC gets to do the lifting & carrying. Camera-op/DoP doesn't do such a menial task as actually making sure the picture is sharp all by themselves, they have people to do that ;) – Tetsujin Sep 30 at 12:46
  • I would do that if I were more than a 1 man crew, I'm using this camera for hobby photography and also for doing interviews and on the ground reporting so if I could utilize the a6400's marvelous AF capabilities with the optical quality of old and cheap vintage lenses that'd make my work much easier. Of course if I were to do a well produced movie I'd get other people to manage the focus etc... Also I cannot upvote the answer because I lack 5 rep rn – R3D34THR4Y Sep 30 at 14:46
  • I understand what you're trying to do, & appreciate the idea might work in theory if you can figure out the comms between the two - I just think a stills camera's AF is going to want to be too fast for the mechanical structure. My guess is it would hunt like crazy because it will keep trying to correct for an image that hasn't managed to finish its last command to move. Also… "Real DoPs don't use AF" ;) – Tetsujin Oct 1 at 7:03
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No. At least not in any of the current DSLR and mirrorless camera systems (Canon, Nikon, Pentax, Sony, etc.). Their autofocus sensors are not exposed to any APIs or control over USB.

Conceivably, it might be possible using something like the Canon Hack Development Kit (CHDK), for at least some bodies. But that "conceivably" is only if a bunch of reverse engineering is put into the effort. And even then, that's on a camera-by-camera basis, far from universal across all of Canon's lineup.

I'm not aware of any CHDK or MagicLantern-like frameworks or toolkits for Sony cameras.

  • I thought it could be theoretically possible with ML on Canon through the USB and by extension with either modded firmware or reverse engineering the IO on the E-mount side for sony cameras, I'll look into the protocol used for E-mount AF lenses and figure out if there's a way to arduino something onto it – R3D34THR4Y Sep 29 at 17:20
  • "Their autofocus sensors are not exposed to any APIs or control over USB." So use live view and implement contrast detection. – Peter Taylor Sep 29 at 21:45
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    @PeterTaylor I mean, yeah, a “solution” can be cobbled and hacked together. But now we’re probably talking an external rasp pi or something. Not something I’d think is practical for actual real world use in order to avoid spending money on native AF lenses for the vast majority of shooters. – scottbb Sep 29 at 21:51
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    I absolutely agree that it's more a crazy geek project to do for fun per se than a sensible approach to getting good photos. But it strikes me that there's a fair chance that anyone who asks about it is at least in the vicinity of crazy geek. – Peter Taylor Sep 30 at 7:13
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    @scottbb The a6400 also supports clean HDMI output so it could be possible to use a Raspberry pi with an HDMI capture card and some custom software to apply contrast detection to the input and drive the AF motor accordingly but that also seems sub-optimal as the Sony camera could theoretically do all of the processing by itself. I don't think camera manufacturers have any interest in letting people tweak their cameras to use old lenses effectively since they also sell lenses themselves haha. – R3D34THR4Y Sep 30 at 11:05
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What might suit your needs is a gadget colloquially called a techart adapter - this is a motorized helicoid adapter that converts Sony-E/NEX to LTM mount, and can be used with something-to-LTM adapters. Since the a6400 is a PDAF camera, it should work well. This will, however, not be good with internal focusing lenses or most zooms (both hate it if you play games with their flange distance - and that is how the techart focuses. Also see below on zooms).

Mind that many of the vintage lenses that can still satisfy on a 24MP APS-C are NOT on the super-cheap side (28/35/50mm primes excepted - and there are caveats with using them wide open and/or at night, esp fast 50mm of all-spherical design). Most manual focus era consumer zooms will frustrate you. Some zooms I found reasonanly usable from experimenting: Series 1 70-210 1st version (Ellis Betensky's design. More of a prosumer zoom, not always sold cheap), some generic 28-50mm, Sigma 75-300 APO DL (More of a prosumer zoom, also more early AF era, will usually need maintenance).

  • I've heard about the Techart/Viltrox adapter that moves the lens away for the sensor to focus but that seemed like a non-optimal approach to focusing to me (plus those are pretty expensive and don't do well on a lot of lenses) I'll look into the zooms your recommended though. (cannot upvote, not enough rep) – R3D34THR4Y Sep 30 at 11:00
  • For so called unit focusing lenses (many primes are), moving them away from the sensor is exactly what the lens mechanism does to focus them. – rackandboneman Sep 30 at 12:56
  • Hmm so I guess that'd work well with some of my vintage primes, though I heard through reviews that the performance of the techart adapter isn't nearly as great as any AF lens, though if you have one you could correct me on that – R3D34THR4Y Sep 30 at 14:48
  • Opinion: When you have time to use a prime lens, you usually have time to MF. – rackandboneman Sep 30 at 16:29

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