This page is out of date. I'm currently awaiting delivery of an adaptor, and I'll update it when I've had time to play with it.
Recently there have been a number of chips on the market that provide autofocus assistance to the camera for lenses which don't have such a function. They're not expensive; prices start at about US $27 (including postage) and go up to about double. Then there are the chips by themselves, which aren't much cheaper, about $24 including postage, and which you have to glue to an adaptor or to a lens.
The following discussion includes links to eBay items, which will soon become invalid. For the moment, though, it's convenient to have something to point to.
The best documentation I found was from tagotech in Singapore, who provide all the information I need online—I wish the others would do that. Unfortunately, they only supply the chips, not the adaptors. I could make one, I suppose, but it would be more expensive, and for a first attempt I'd rather try a pre-assembled adaptor.
The question is, what do the chips do? The tagotech documentation goes into great detail about setting apertures, focal length, front or back focus and a name for the EXIF information. They also mention things like shutter release delays (none for this chip, up to 1 second for others).
What do the others offer? GadgetInfinity states that their adaptor doesn't work in P or S modes. cam.plus notes that you have to half-depress the shutter button for it to work. I assume that's the same with all of them, since otherwise the camera isn't paying attention to focus. It seems that the adapter has the same exposure mode limitations as the GadgetInfinity device. Both of these people are in Hong Kong; could it be the same chip?
Apparently RJ camera accessory store, somewhere in China, has a different adaptor : like the ones from Hong Kong, it works in manual or aperture priority mode, but with all autofocus modes. It doesn't mention depressing the shutter release button, but it doesn't change the aperture display. It doesn't seem to work too well with apertures below f/8, which could be a problem with long telephotos.
So, which one? The tagotech people point out that the focal length must be set correctly for image stabilization to work. The default settings in the camera firmware don't apply, because the camera sees an autofocus lens. So an adaptor that doesn't allow you to set the focal length is at a disadvantage.
On a roundabout way found a description of the Dandelion adaptor chip. Judging from the similarities in the text, it's reasonable to assume that the tagotech device is really a Dandelion. But why is the other documentation so different? The Dandelion site also has a link to a video demonstration of setting up the parameters; given the complexity, that's a good idea.
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