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Modifying an Old Nikon AI-S 300mm f/2.8 Lens to Give it Faux Autofocus

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nikon300mm

If you’d like to use legacy Nikkor lenses on your modern Nikon camera, one thing you can do to improve functionality is add a CPU to them. While there are services out there that can convert your lenses for a fee, you can also buy the programmable component for $30 on eBay and do it yourself.

That’s what photographer Kalafok Vlakostnitsj recently did with his Nikon AI-S 300mm f/2.8 lens.

A listing for a Nikon lens CPU chip on eBay
A listing for a Nikon lens CPU chip on eBay

Vlakostnitsj, a 25-year-old photo enthusiast and mechanical engineering student, had to do a bit of extra work for his mod. While some lenses have mounts that allow you to simply glue the CPU in place, the old AI-S 30mm f/2.8 has a thick metal ring section where the chip needs to go, so Vlakostnitsj had to cut out a chunk of the lens.

lens

He spent four hours in a metal shop with a Deckel FP1 milling machine and a Hembrug Ergonomic lathe in order to precisely mill the slot out. The part on the lens is fragile and irreplaceable, so one needs to do this step very carefully.

The fixture used
The fixture used
The cutting begins
The cutting begins
After the section was cut out
After the section was cut out
Before inserting the chip
Before inserting the chip
After the chip is glued into the lens mount
After the chip is glued into the lens mount

“The lens modification improves its usability,” Vlakostnitsj tells us. He can now use his camera controls to set the aperture, making shooting with the lens more convenient. EXIF data for focal length is also correctly saved in resulting photos.

One of the biggest benefits, Vlakostnitsj says, is the fact that the lens now has poor man’s autofocus. You simply hold down the shutter on your camera, manually focus the lens, and the camera will capture a photo immediately when sharp focus is detected on your selected autofocus point.

The camera is tricked into believing that your manual focusing is the focusing motor at work. “It is pretty simple to get sharp pictures of birds in flight,” Vlakostnitsj tells us.

The photographer says he is offering his own lens conversion services to interested Nikon shooters. You can get in touch with him here to discuss details.


P.S. You can learn more about all the benefits of adding a CPU to manual focus lenses here. The article also has instructions on how the mod is done.

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