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07-17-2010, 01:56 AM   #1
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k-x af motor and lens adapters

hello i'm interested in looking to buy a good camera for my architecture studies in university and have done a lot of research on the k-x. i curretnly have an old nikon film slr that came with two lenses (one af zoom kit lens and the other an af macro lens). I have seen lens adapters for pentax that would allow me to use the nikon f mounts on the k-x but would like to know if the in body af motor in the k-x would work with the f mount lenses through the lens adapter.
also
if this would not work, would i be able to use older manual only k mount lenses with the k-x and be able to use those lenses in af because of the in body motor?

07-17-2010, 02:46 AM   #2
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no and no

simply put, no and no
07-17-2010, 08:59 AM   #3
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No way is the Nikon kit zoom worth the hassle of trying to use through such an adapter - far too many compromises comapred to just getting the K-x kit zoom. The macro lens *might* be worth trying, though. Macro photogrpahy is almsot never done with AF anyhow. If you get one of the adapters with no optics, you won't lose image quality, and while you give up infinity focus, that's irrelevant for macro photography (actually would presumably allow you to focus slightly closer).
07-17-2010, 10:00 AM   #4
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thanks for clearing that up
i was actually gifted the nikon film quite recently and have never had any previous experience with slr cameras, so i am completely new to this.
then what exactly does it mean when pentax says that the in body af will allow all the lenses to be used with the camera? isn't that already enabled because of the usage of the compatible k mount? what is the advantage of having in body af if it will not be able to enable af on manual lenses?


Last edited by sharkbait88; 07-17-2010 at 10:05 AM.
07-17-2010, 10:20 AM   #5
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It works with all AF lenses, and there are advantages to in-body AF, including less expensive lenses.
07-17-2010, 12:17 PM   #6
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If the lens is an AF lens for Pentax, then it will AF with the K-x. this is in stark contrast to Nikon, where most ofthe inexpensive bodies *won't* AF with many AF lenses (they only do AF with the newest AF lenses). But on both Pentax and Nikon if the lens is not an AF lens, no body will make it become one.
07-17-2010, 12:32 PM   #7
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QuoteOriginally posted by sharkbait88 Quote
...then what exactly does it mean when pentax says that the in body af will allow all the lenses to be used with the camera? isn't that already enabled because of the usage of the compatible k mount? what is the advantage of having in body af if it will not be able to enable af on manual lenses?
Pentax cameras can AF on all Pentax (or Pentax mount) AF lenses. It can not AF on Nikon lenses, AF or not.

It can not AF on Pentax manual lenses because manual focus lenses lack the mechanism that interfaces with the in-camera AF motor. If you look at the lens mount on your camera at about the five o'clock position, you will see a little drive coupler that fits into a matching drive slot on an AF lens. This slot turns and is connected to the focus mechanism of the lens. MF lenses do not have this coupling.

Pentax has only said that all Pentax lenses will work with their dslrs. They never said that old lenses would magically gain new functions that they didn't have when they were built.

Years ago, Pentax did make a teleconverter that could AF a MF lens. The teleconverter had the link. It also had a helical focusing mechanism that would move the lens toward/away from the film plane to achieve the focus. I've never used one, but I believe that it was somewhat limited in its ability to focus all AF lenses. Perhaps that's why Pentax never repeated the experiment and don't make that TC today.
07-17-2010, 08:52 PM   #8
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thank you all very much!

07-18-2010, 08:01 AM   #9
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A bit more on Nikon, Pentax, and automation:

Older Nikon lenses can usually be fairly safely force-fit onto a Pentax (PK) mount. Or minor surgery can be performed: I've modified two Nikon AI-mount lenses with a Dremel Moto-Tool with metal-cutting blade, to remove some slight protrusions for a tighter fit. And I'm no machinist. It's easy. But it's permanent, and the lenses still won't lock-into the Pentax mount. Don't handle carelessly.

I have one newer Nikon-mount AF lens, and it does NOT force-fit safely onto a PK mount. It might, with the slight surgery. (I must decide: is the pristine Sigma AF 70-300mm f/4-5.6 D APO Macro zoom that cost me US$9 worth modding, or worth more selling? But that's my problem, not yours.)

When using ANY non-Pentax-AF lens on a Pentax AF camera, that lens becomes totally manual in focus and aperture. As mentioned, with macro lenses that's no big deal, as most macro work is manual. With any lens that fits a modern Pentax dSLR, AF can be approximated with Catch-In-Focus aka Trap-Focus. Search the discussions here for more on CIF. I use CIF with my modded Nikon-mount lenses, no problem.

But focus is only one factor; aperture is another. An auto lens with no aperture ring isn't very useful manually, as the iris is either stuck wide-open or shut-down. (I happen to have two lenses, a 24/2 and a 25/3.5, both stuck open, but they're sharp enough that I shoot them anyway.)

Bottom line: I suspect that your unspecified Nikon kit lens has no place in the Pentax world. Your macro lens might, depending on its construction -- what model is it? If it's an AF lens, probably not.

As for architecture, I recently almost bought an old Nikkor 105mm PC (perspective control) lens, hoping to mod it for Pentax. A risky hope, eh? As mentioned, other PC lenses are available. But PC can also be handled in software. Shoot the shot, correct it, shrink the image a bit to tighten resolution in the corrected area, etc. I think most modern image editors have this capability. It's cheaper than a lens.
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