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I just bought a Nikon D5500 with 35mm f1.8. I also have a Nikkor 70-210mm AF (that doesn't focus automatically). I learned that using a TC-16A AF Teleconverter 1.6X might help but i was informed that my camera would need some kind of modification to make it work. Is there another teleconverter that will make old lenses auto focus using my D5500? I'm planning to buy some old AI lenses from Japan because those are awesome. Is modifying my camera a good idea? How do I proceed? Please help. Thanks.

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How can I modify my NIkon D5500 so I can make a vintage lens auto focus?

You can't.

I learned that using a TC-16A AF Teleconverter 1.6X might help ...

Whatever you learned is probably wrong. From my googling it looks as if the TC-16A was designed to turn AIS lenses into AF lenses (i.e., an interim step to add electronic communication and the physical linkage to the AF system in the camera body), and that AF lenses are incompatible with it. And you'll still need a focus motor, which your D5500 does not have. In addition, to work on the modern Nikon dSLRs, the TC-16A must be modified.

Is there another teleconverter that will make old lenses auto focus using my D5500?

No. You're missing a focus motor in your camera body, and in the AF lens. The TC does not have a motor of its own, and expects your camera body to have one.

I'm planning to buy some old AI lenses from Japan because those are awesome.

They are. But they are manual focus. Not even AIS, so the TC-16A won't help you with them. Also while you could get pre-AI lenses and use them, be aware they're liable to damage a higher-end body than a D5x00 without modification (grinding down an arm).

Is modifying my camera a good idea? How do I proceed?

If you don't already know how to proceed, and you don't already have a really good working knowledge of soldering, microelectronics, prototyping, a thirst to figure out how to stuff works and to build things (along with a buttload of money), I'd say it's probably not "a good idea." Because you have to add/integrate a focus motor into the body. And that won't be trivial or easy and probably can damage the camera if you've never done anything like it before.

The least painful and expensive route is more likely to be returning your D5500, and saving up for a D7x00 or used D90 body, and then looking into an modified TC-16A if you get AIS lenses.

  • For completeness, there is actually a device like that - but for Sony E, not Nikon. Google "techart pro". – rackandboneman Oct 30 '18 at 13:09
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This question (or a variation on it) pops up periodically, and one thing that I think hasn't received much attention is how much more there is to this than "adding an autofocus motor" eludes to. (And, I enjoy exploring into the realm of the somewhat ridiculous.)

Honestly, adding an "autofocus" motor is not going to be hard. Grab a small and speed-reduced motor, such as a Lego Power motor and use a rubber band to attach the motor driveshaft to the lens focus ring. Rig up some sort of assembly to hold tension on the rubber band. Sticking with Lego, a control switch would let you turn the focus motor on and off. You could even tape that control switch near your shutter release so that you can operate it while looking through the viewfinder. Bam! Done! Autofocus!

(As a side note, something neat about this is that you're not just getting autofocus with the AF and AF-D lenses, but you can add this to AIS and older manual focus lenses, too!) All for under $30!

You've now got a frankenstein camera with a motor hanging off the lens and a switch taped near the shutter release, and the battery box taped to the bottom of the camera. Hey, it works (-ish), but you want something better. Especially after you realize that hitting the switch on-off-on-off to try to hit focus is an incredibly touchy operation.

Now it gets complicated very quickly:

  • You want to eliminate the separate battery for the Lego motor. Can you tap into the camera's battery power? Given that the camera's battery is already performing functions for the camera, running the Lego motor will have an impact on the battery life, at the least.
  • You want to press the shutter release to cause autofocus to function, just like with an AF-S motor. That shutter release button belies a more complex operation: it triggers the lens to focus in either direction with a single touch; in other words there's logic at play to determine when the scene is in focus. Simply soldering the Lego motor leads to the shutter release button will not grant that capability. To actually take advantage of the focus logic in the camera you're going to need to understand how the camera works and how to modify it (electronics and programming/firmware work ahead).
  • Switching lenses is an operation. Removing the frankenstein'd lens also means modifying the body. Attaching another frankenstein'd lens means modifying the Lego motor rig or carrying a separate rig for each lens (lenses are different sizes, after all).

It may make more sense to purchase an extra AF-S lens for some help. You could determine which lens contacts control the AF-S motor in the lens, and that could be frankenstein'd to the Lego motor. (Well, probably not -- AF-S motors are sensored brushless motors specifically so that the AF logic can know the motor position. So, swap in a small brushless motor -- perhaps I can pull one off of an RC car to make the fastest focusing lens ever.) Anyway, using the AF-S lens contact and circuitry hooked up to the RC car motor with a rubber band could then get the capability on the old 70-210mm AF lens. It'll only cost $100 for a cheap AF-S lens (a used 18-55 could probably be found for that price), perhaps $35 for a brushless motor, a rubber band (free from your mail), and you'll need to build some sort of assembly to hold the motor onto the lens. Total: under $150 to be able to "use" the old lens.

Or, $160 for a 55-200 mm AF-S that will autofocus on your camera -- likely faster than the 70-210 could AF on any camera, and likely provide sharper results and better color, too.

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