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01-26-2009, 07:58 PM   #1
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It's taken me this long to realize...

that the 3 years I've owned a pentax SLR, the kit 18.55mm lens does not have a built in AF motor?

Reading a review of the D60 on dpreview.com I came across a CON they wrote, they said that it did not come with a AF driveline on the lens mount for lenses that have no built in AF motor. I took my lens off and looked.. to realize, wow, yes there is a driveline shaft-dealio that connects from the camera to the lens to drive the lenses AF.

This must be why my k20d focuses my girlfriends lenses faster than her k200d, i thought it just shot more voltage into the AF motor of the lens.


I didn't even know this was ever a property of an SLR, i had no idea they had built in AF motors inside of the camera.

What's the advantage/disadvantage?
What's the advantage of lenses that have their own dedicated AF motor? Which lenses that pentax offers have a built in AF motor?

Curious.

01-26-2009, 08:03 PM   #2
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The first AF cameras with interchangeable lenses used in camera motors to drive the focusing helicoid. Later was invented the in lens motors. In the case of the lesser priced Nikons, they saved money on the body by leaving out the motor and drive assembly. This restricts them to only the lenses that have motors built in. Canon's mounts have only in lens motors. And so it goes.
01-26-2009, 08:03 PM   #3
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How did you not know? It squeals like a stuck pig.
01-26-2009, 09:39 PM   #4
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An AF motor built into a lens can be optimized for that lens. The amount of lens element travel for a wide angle lens is significantly less than for a long telephoto therefore motors with different speeds can be used. The AF module in the camera must be able to keep up with the motor in the lens of course. Pentax's name for their in-lens motor technology is SDM.

01-26-2009, 10:24 PM   #5
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I think the basic version is: in-lens motors are generally better, but more expensive since you have an added cost in each lens. Plus the lens now has something extra to break down.
01-27-2009, 12:11 AM   #6
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I kinda made that same discovery a month before you did.
01-27-2009, 08:15 AM   #7
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QuoteOriginally posted by steve500 Quote
Reading a review of the D60 on dpreview.com I came across a CON they wrote, they said that it did not come with a AF driveline on the lens mount for lenses that have no built in AF motor. I took my lens off and looked.. to realize, wow, yes there is a driveline shaft-dealio that connects from the camera to the lens to drive the lenses AF.
It's a "con" for Nikon D40/40X/60 cameras because there's a whole bucketload of lenses that don't autofocus on those cameras. Their cheap AF 50mm F1.8/F1.4 D doesn't AF on those bodies. as do any lens that isn't AF-I or AF-S. you have to pay the extra money for the AF-S 50mm F1.4G or the Sigma 50mm HSM

Makes no difference to Pentax as all but the Sigma HSM lenses, the DA17-70 F4 SDM and the 2 latest DA* lenses use the in-body screwdrive AF motor.. the other DA* lenses have both Screwdrive and in-lens SDM

(the ME-F's 35-70 F2.8's lens doesn't count. it's MF on every other K-mount camera)

QuoteOriginally posted by steve500 Quote
This must be why my k20d focuses my girlfriends lenses faster than her k200d, i thought it just shot more voltage into the AF motor of the lens.
your K20D focuses faster because it can acquire focus better.

QuoteOriginally posted by steve500 Quote
What's the advantage/disadvantage?
Disadvantage: cost. if you're not going the whole hog and having an SDM motor in your lens, it's just going to increase the price of the lens. look at the same lenses by tamron/sigma for Nikon that have one variant without in-lens motor, and one with in-lens motor. the in-lens motor one is more expensive

Disadvantage: size. you're not getting DA40LTD sized lenses with in-lens AF motors

Advantage: Speed, but only with a Supersonic motor. as an example, the Tamron 18-250 with built-in motor for Nikon and Canon is no faster or quieter than the in-body lens drive of the Pentax.

Advantage: Full time Manual focusing, again, only with a supersonic motor. . sure, you can tweak with Quickshift (if your lens has it), but i can have my hand on the focus ring on the DA*50-135 while it focuses, and then tweak it. you can't do that with quickshift.

not every "in-lens AF motor" lens out there uses this funky Supersonic drive. it costs more, so it's only in the good lenses. Canon's 18-55 II and 18-55 VR have a standard micro-motor inside of the lens. it's no better than in-body screwdrive.

QuoteOriginally posted by steve500 Quote
Which lenses that pentax offers have a built in AF motor?
any Pentax DA* lens.
the Pentax DA17-70 F4 SDM
Any Sigma with HSM, currently the 24-70 F2.8 HSM, 50mm F1.4 HSM, 50-150 F2.8 HSM II, 70-200 F2.8 HSM II
01-27-2009, 09:17 AM   #8
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The DA 17-70/4 SDM's focusing ring moves during autofocus (so not recommended to hold it while autofocusing) but it retains quickshift-functionality...so I wouldn't include this as a general SDM benefit. It is however quiet and fast.

There's probably also some truth to faster AF on the better-powered Li-Ion bodies (K10D/K20D) vs. the lower-powered AA bodies, particularly if they're running on even lower-powered NiMH batteries. But there *may* be mildly improved AF logic as well in the higher-end bodies.

01-27-2009, 09:56 AM   #9
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What do you mean the kit lens doesn't have a built in AF motor?
01-27-2009, 10:47 AM   #10
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in-lens motors that aren't ring motors are hardly any advantage over in-body motors

ring motors wrap around the lens and give much more precision

micro motors are basically the same as having the motor in body only without the shaft
01-27-2009, 02:10 PM   #11
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QuoteOriginally posted by Leaf Fan Quote
What do you mean the kit lens doesn't have a built in AF motor?
The AF motor is in the camera body. If you look on the mount on the body, you'll see a protrusion on the lower right (about 5 o'clock) of the mount. That corresponds to a slot on AF lenses.

The body turns the screw, which focuses the lens.
01-27-2009, 08:42 PM   #12
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QuoteOriginally posted by kristoffon Quote
in-lens motors that aren't ring motors are hardly any advantage over in-body motors

ring motors wrap around the lens and give much more precision

micro motors are basically the same as having the motor in body only without the shaft
"Hardly any advantage" ... unless you need the virtual silence of the SDM lenses. Then they have an unbeatable advantage. My DA* 300 is pretty damn precise, thank you.

Jack
01-27-2009, 09:33 PM   #13
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QuoteOriginally posted by nakey Quote
It's a "con" for Nikon D40/40X/60 cameras because there's a whole bucketload of lenses that don't autofocus on those cameras. Their cheap AF 50mm F1.8/F1.4 D doesn't AF on those bodies. as do any lens that isn't AF-I or AF-S. you have to pay the extra money for the AF-S 50mm F1.4G or the Sigma 50mm HSM
Also, older Nikon lenses don't *meter* with anything short of a dx00, which is why I'm not shooting Nikon for digital, now. I mean, don't get me wrong, I love my Pentax, and especially the Pentax community, but I could have gotten the deal of a lifetime on AIS glass that would have me pretty much kitted out for the forseeable future... but I couldn't make the numbers work out cause a digital body to use them on would have been way out of reach. If I could have stuck em on a d40, I'd have worked my way along that way.

*Big* drawback, there. Actually, I hope Pentax works better M lens compatibility back into future models, somehow, that old glass just is such a gateway into the system, and they've got no problem making Limiteds and stuff everyone wants anyway.

(And on a historical note: most of the first AF SLRs (Like Pentax's ME-F , the Canon T-80, etc, actually *had* the motors in the lenses, ...but with the technology of the time, this way just meant the lenses were ungainly, what with the batteries and motors in there. )
01-27-2009, 10:36 PM   #14
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QuoteOriginally posted by AndrewG NY Quote
The DA 17-70/4 SDM's focusing ring moves during autofocus (so not recommended to hold it while autofocusing) but it retains quickshift-functionality...so I wouldn't include this as a general SDM benefit. It is however quiet and fast.
Well, that's pointless. i wonder why they'd use the Micro Supersonic motor in that lens when the in-body drive would be sufficient.

It'd be worth it if they did use Ring-type SDM motors instead

QuoteOriginally posted by Ratmagiclady Quote
Also, older Nikon lenses don't *meter* with anything short of a dx00,
I thought so, but didn't wanna say it cause i'm not exactly sure about it. a Dx00 body just to meter with the AI-S lenses. that makes me cry
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