AF-converter for manual-focus lenses?

[AgX]

In a photographic encyclopedia (I’ve got several…) I found this:

Autofocus-Converter
Opto-mechanichal module which enables the use of manual-focus lenses on autofocus-cameras and auto-focussing, increasing focal length (typically by factor 1,4).

I can’t remember to have come across such a device neither in real nor in literature. (Well, perhaps I should not trust my memory…) The use of the word `typically´ even suggests that there are/were several of such devices.

Does anybody know more?


EDIT:

I just realized those were at least the Nikon TC-16 and -16A (I just found them in the book by Moose Peterson).

SORRY! (I can't delete this post.)

 

[David A. Goldfarb]

Might as well leave it up. I didn't know there were such things.

There was the Contax AX that had autofocus in the body, so that it could use manual focus lenses. The concept was great, but I gather that autofocus was slow compared to systems that put the autofocus in the lens.

AF in the body or through a converter would also mean missing out on floating element lens designs for close range focusing, but those are often manual focus situations anyway.

 

[Struan Gray]

Pentax had one:

http://kmp.bdimitrov.de/teleconverters/F1.7X.html

 

[monkeykoder]

That is kind of a cool idea glad you brought it up. I would never want it but still cool.

 

[PhotoJim]

They worked but you had to have the lens focused at infinity usually. For nearer subjects you would have to manually focus the lens closer, so that the converter had enough range to be able to put the subject in focus.

They were a kludge, IMHO, and only interesting as curiosities. The AF speed was not particularly good so their utility was limited.

 

[AgX]

I admit it took me a while to realize what that FL factor was about. As at the first moment I thought of a device, controlled by the body, twisting the focus barrel of the lens. (Seemingly I have a real retro-day...) Then I realized that the whole article would only make sense concerning a focussing lens element making part of a converter. And so it turned out to be.

It further turned out that I never read that Peterson book completely. I mean there are so many Nikon converters, do I really have to read about each detail of each of them? Seemingly, yes.
But aside from that FL-factor (similar to a standard tele-converter), those Nikon converters had the disadvantage of a limited focus range.
Thus one had to roughly focus the lens manually, and then let the converter do the rest. Not that bad.
But I guess if the converter has just gone to its limits, even with roughly prefocussing for a new shoot it might not have been able to focus.
(I see, PhotoJim just hinted at the same point.)

 

[AgX]

AF in the body or through a converter would also mean missing out on floating element lens designs for close range focusing, but those are often manual focus situations anyway.

That is an interesting remark, David. I never thought of that Contax concept of focussing via the back omitting the benefits of floating elements.
(Though, if the lens had floating elements one could/should pre-focus.)

 

[domaz]

It would be interesting to design one that actually did turn the barrel of the lens to focus. You would need to retrofit some autofocus mechanism in the body though.

 

[AgX]

Actually the first Canon AF-lens (for the FD system) seemingly was samething like that.
It was a self sustained unit consisting of a standard 35mm lens with I assume a somewhat redesigned barrel, focussing drive, batteries, a rangefinder, a Honeywell type of sensor unit and control board, all in a big housing.


Actually, it was not a 35mm prime lens, but the 35-70mm zoom lens.

 

[David A. Goldfarb]

Yes, I remember that AF FD lens. Autofocus was said to be slow, but it was a major innovation.

Before that, around the time of the Canon EF body (not to be confused with the EF mount), Canon made an auto-flash system that involved attaching a ring to the front of a few certain lenses, and the ring could detect the focus distance (and thus the flash distance) by measuring how far the focus ring had been turned, so some of that technology had already been developed before it was applied to autofocus.

 

[pentaxuser]

Pentax had one:

http://kmp.bdimitrov.de/teleconverters/F1.7X.html

One came up on U.K. e-bay a few weeks ago. Pentax manual lenses are so common and relatively cheap that I thought about getting it so I could convert manuals to AF. Then I checked the auction prices and changed my mind

They seem to be much sought after and very scarce, hence the price

pentaxuser

 

[AgX]

As I referred to that selfsustained Canon AF production lens, there is an even earlier prototype of such made by Nikon in 1971 (F/4.5 80mm).
As it it is huge for its FL and aperture I guess there might have been a beamspitter to project center imge detail to the AF control avoiding parallax. But that is just a guess, but the best photo of it I found in one of my books on the bookshelve, and there are definitely no rangefinder windows on the control housing.

 

[AgX]

Back to those AF-converters:

Actually they are merely a focus actuator (via their own optics), but the focus control is done by an AF camera-body.

But what could be done with them at a manual focus body? Well, with some wiring, a power source and a switch you could actuate the lens of your choice. But the use of a rocker-switch does not seem to yield any advantage on turning a focus barrel by hand, it rather would be the contrary.

However, in a situation where access to the lens barrel is limited, such a modified converter could be an outcome. For instance in an underwater housing of the bag type, where it is hard to turn the focus barrel of longer lenses.