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06-17-2017, 06:07 PM   #1
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Hi there. Screw drive vs PLM pulse.

Hello to you all. Bear with me this is my first thread so hear goes. I'm looking to upgrade from an older Tamron 70/300mm for my K5 and I'm looking at two Pentax options. One is described as pulse AF (PLM) and the other is described as Screw drive AF. How does Pulse work and is it compatible with a K5?

06-17-2017, 06:13 PM   #2
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Hello Michael welcome to the Forums. I can not help on your question but there are others her that can. So I will let one of them field the question.
06-17-2017, 06:26 PM   #3
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Welcome, Michael!
Screwdrive = focusing elements are driven by a motor in the camera though a mechanical connection. This system is rock solid, proven over decades. However, it can be noisy depending on the lens and focusing speed is restricted to the motor speed. All Pentax AF cameras use this system so compatibility is assured.

PLM = focusing elements are driven by a motor in the lens itself. This was introduced with the KAF4 mount. According to Ricoh it is compatible with the k-3 and newer. I believe it was not compatible with the k-3 at launch and a firmware update added that. Cameras listed as compatible are: K-3, K-3 II, K-50, K-70, K-S1, K-S2, KP and K-1.

So unless something is changed with a firmware update (unlikely at this point) your K-5 will not work with PLM lenses. It most certainly will work with any screwdrive lens.
06-17-2017, 06:34 PM   #4
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QuoteOriginally posted by jatrax Quote
Welcome, Michael!
Screwdrive = focusing elements are driven by a motor in the camera though a mechanical connection. This system is rock solid, proven over decades. However, it can be noisy depending on the lens and focusing speed is restricted to the motor speed. All Pentax AF cameras use this system so compatibility is assured.

PLM = focusing elements are driven by a motor in the lens itself. This was introduced with the KAF4 mount. According to Ricoh it is compatible with the k-3 and newer. I believe it was not compatible with the k-3 at launch and a firmware update added that. Cameras listed as compatible are: K-3, K-3 II, K-50, K-70, K-S1, K-S2, KP and K-1.

So unless something is changed with a firmware update (unlikely at this point) your K-5 will not work with PLM lenses. It most certainly will work with any screwdrive lens.
Wow, that was quick and helps with my decision. (Saved some money too I think.) First experience with the forum was a hit. thanks Patrick9 and jatrax.

06-17-2017, 08:00 PM   #5
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It appears from your post you are looking at the Pentax 55-300. This lens comes in a number of different versions although the optics appear to be identical. This forum maintains a lens database, look at the top under "lenses". Here is a link to the page with the DA 55-300: Pentax DA Zoom Lenses - Reviews and Specifications - SLR and Interchangeable Lenses - Pentax Lens Reviews & Lens Database

The original version DA 55-300 F/4-5.8 ED also came in a DA L version. This was sold only as part of multi-lens 'kits' but is widely available second hand. If budget is a priority you might take a look at the DA L version, optically identical to the DA version but does not have quick-shift or a hood. The DA 55-300 F/4-5.8 ED WR version was introduced in 2013 I think and includes weather sealing. The new DA 55-300 F/4-5.8 ED PLM WR RE version was recently introduced and is the first version with an in-lens AF motor. I have not seen an optic diagram of this lens but it is likely (but I do not know) that the optics are different in this version to accommodate the PLM motor. It does get good reviews, but unfortunately is not backwards compatible.
06-17-2017, 09:57 PM   #6
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QuoteOriginally posted by MichaelS Quote
Hello to you all. Bear with me this is my first thread so hear goes. I'm looking to upgrade from an older Tamron 70/300mm for my K5 and I'm looking at two Pentax options. One is described as pulse AF (PLM) and the other is described as Screw drive AF. How does Pulse work and is it compatible with a K5?
PLM autofocus doesn't work on the K-5. It is however MUCH faster to focus than any other Pentax lens, even those with DC silent focus. If you plan to upgrade your body to a K-3 or newer eventually, the 55-300mm PLM is the way to go.

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06-18-2017, 12:47 AM   #7
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I'll just say welcome, as all these knowledge folk here have already answered your question.
06-18-2017, 07:52 AM   #8
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Welcome to the forums.

06-18-2017, 09:20 AM   #9
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Welcome to the forum.
06-18-2017, 09:50 AM   #10
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QuoteOriginally posted by Adam Quote
PLM autofocus doesn't work on the K-5. It is however MUCH faster to focus than any other Pentax lens, even those with DC silent focus. If you plan to upgrade your body to a K-3 or newer eventually, the 55-300mm PLM is the way to go.
IIRC the 55-300 PLM has the new KAF4 electronic aperture, which won't work at all on a K-5, not even as manual focus.
06-18-2017, 04:10 PM   #11
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QuoteOriginally posted by Cthulhugan Quote
IIRC the 55-300 PLM has the new KAF4 electronic aperture, which won't work at all on a K-5, not even as manual focus.
Correct, it will always shoot wide-open. Manual focusing should work, though.

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