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02-04-2008, 03:03 PM   #1
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In-Body autofocus vs In-Lens autofocus

Pentax has had in-body autofocus for awhile now, this is great because you can use many lenses from various generations to their fullest.

one of the other pluses has been the fact that as lens manufacturers, autofocus motors need not be implemented in the lens themselves, making the lenses physically lighter and smaller.

all great pluses!

but the new lenses do not exhibit these tendencies, and it seems pentax has pushed for in-lens autofocusing motors over the in body. I can totally understand this since at this point in time its both quieter and faster, no denying, but the real question i have is why did pentax decide to abandon further development of in-body autofocusing

if one of their strongest selling points is backwards compatibility, why not invest into high end in-body design and have some of the older lenses autofocus with the best of them, while having the brand new lenses lighter and compact compared to the competition.

02-04-2008, 03:11 PM   #2
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They haven't abandoned in body AF as all the SDM lenses do both.

The 16-50, 50-135, 17-70, 200, 300 DA*'s all will work with the in body AF motor. They even have the 18-55 II, the 55-300, and the 35 macro which all are made just of in body AF. The only time the SDM motor in the lens works is with a K10D (that has proper 1.3 firmware), K100D super, K200D and K20D cameras. If it's on any other camrea or K10D firmware it will AF with the old fashioned in body motor.

Hope this helps answer your statement.
02-04-2008, 03:14 PM   #3
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well i dont mean abandoned in the sense that they will take it out, obviously its wise to keep it in so you can use the older lenses

i'm more intersted in why they stopped developing it further as a feature that could set the camera apart from the rest of the pack.

imagine being able to focus your FA Limiteds with the speed and precision of modern HSM lenses?

or am i asking for the impossible, i mean, there are always smart engineers out there.
02-04-2008, 03:19 PM   #4
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The small pin that spins inside the lens for in-body AF doesn't have the force to quickly start and stop like HSM. Imagine the amount of force needed to twist a small wooden dowel back and forth and that small rotation gives you very small movement in the lens. If you go too fast and try to stop and go back the other direction you'd physically twist the metal and maybe even damage it. The Pentax SDM uses gears that start and stop with a pulse of electricity and not a thin shaft of metal.

The Sony A700 has lighting fast AF with the in body motor, but it's a different technology that Pentax may not be able to due since the older FA lenses may have cheaper or weaker rods.

02-04-2008, 03:36 PM   #5
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You're looking at this from the wrong angle. There's a step in between that you're missing. Pentax's current focusing system has poor low light accuracy and the current cameras requires a focus recheck. The camera body is what's telling the lens to hunt. SDM or screw driven are two separate ways of getting the results the camera body is asking for. When pentax improves their camera's focusing behavior, it will improve both SDM and screw driven applications. In broad daylight, my camera focuses very fast despite being screw driven. The focusing limitations are not in motor, it's in the rest of the focusing system.

However, just to entertain having an even faster body focus motor to turn the element faster, there are other factors to consider. It will require a larger motor to shove in the body, it will reduce battery life, it'll be noisier than a slower equivalent, and it'll make the body more expensive to produce.
02-04-2008, 03:55 PM   #6
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QuoteOriginally posted by AVANT Quote
However, just to entertain having an even faster body focus motor to turn the element faster, there are other factors to consider. It will require a larger motor to shove in the body, it will reduce battery life, it'll be noisier than a slower equivalent, and it'll make the body more expensive to produce.

Maybe you shoulda left that point out of your arguement. Most people carry one or two cameras but have HOW many lenses?... A more expensive camera body vs. many more expensive lenses with AF drives in them... no brainer there.

My question is, I wonder how much noise is added to an image because of an AF motor in the body. Seriously, I don't know if there's a significant impact. But is this a consideration - the additional heat generated by that motor that the electronics have to deal with. I wonder.
02-04-2008, 04:14 PM   #7
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QuoteOriginally posted by TourDeForce Quote
Maybe you shoulda left that point out of your arguement. Most people carry one or two cameras but have HOW many lenses?... A more expensive camera body vs. many more expensive lenses with AF drives in them... no brainer there.

My question is, I wonder how much noise is added to an image because of an AF motor in the body. Seriously, I don't know if there's a significant impact. But is this a consideration - the additional heat generated by that motor that the electronics have to deal with. I wonder.
I don't see why cost should be factored out. Your reply is too black and white. You're forgetting a lot of factors including that not everyone will buy SDM lens. A lot of dSLR owners will live with the kit lens and have no intentions of purchasing additional lens or maybe just one or two "affordable" lens. To those typical consumers (which outnumber us enthusiasts many times over), they will consider a more expensive camera body as a major con. Even us enthusiasts compare camera body prices constantly!

I was referring to operational noise, not noise found on an image.
02-05-2008, 11:10 AM   #8
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QuoteOriginally posted by AVANT Quote
I don't see why cost should be factored out. Your reply is too black and white. You're forgetting a lot of factors including that not everyone will buy SDM lens. A lot of dSLR owners will live with the kit lens and have no intentions of purchasing additional lens or maybe just one or two "affordable" lens. To those typical consumers (which outnumber us enthusiasts many times over), they will consider a more expensive camera body as a major con. Even us enthusiasts compare camera body prices constantly!

I was referring to operational noise, not noise found on an image.
I understand completely, noise & all. I'm just suggesting the typical DLSR user will have a single camera body & a small collection of lenses to go with it. I'm not factoring out the added cost of the body with internal focus drives, I'm just factoring IN the higher cost of the internal focus lenses for consideration in the discussion. They will both have an impact on a purchasing decision.

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