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04-09-2021, 04:31 PM   #61
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QuoteOriginally posted by Tesla Quote
I think KAF2 and newer with a in lens motor such as SDM, DC or PLM are all good for AF-C. I'm sure some motor technologies work better than others, but I think they all preform well. I believe the only difference between KAF2 and KAF3 is that KAF3 drops screw drive support.
Yes, we have no reason to expect one motor technology to work better than the other,
Since the only difference between KAF2 and KAF3 is that KAF3 doesn't supply screw-drive support, I use KAF3 when I want to exclude screw-drive from consideration.

04-09-2021, 04:36 PM   #62
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QuoteOriginally posted by reh321 Quote
Yes, we have no reason to expect one motor technology to work better than the other,
Since the only difference between KAF2 and KAF3 is that KAF3 doesn't supply screw-drive support, I use KAF3 when I want to exclude screw-drive from consideration.
According to some of the early reviewers KAF3 and 4 lenses may be more responsive than KAF or KAF2 on the K3 III
04-09-2021, 04:59 PM   #63
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QuoteOriginally posted by gatorguy Quote
According to some of the early reviewers KAF3 and 4 lenses may be more responsive than KAF or KAF2 on the K3 III
I could be wrong, but I think the response differs because of different motor types. I believe the mount versions just relate to what motors are supported by the mount.
04-09-2021, 05:18 PM - 1 Like   #64
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QuoteOriginally posted by Tesla Quote
I could be wrong, but I think the response differs because of different motor types.
Pretty much
Table of Functions by Mount / Lens lineup/ Lenses / Products | RICOH IMAGING

04-09-2021, 06:50 PM   #65
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QuoteOriginally posted by Tesla Quote
I could be wrong, but I think the response differs because of different motor types. I believe the mount versions just relate to what motors are supported by the mount.
Most likely there is ‘play’ in screw-drive mechanisms, so the in-lens versions are simply more responsive.
04-09-2021, 09:09 PM   #66
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Regarding AF tracking performance of the K-3 III we should find out the realities in a few more weeks / months. Most certainly gains will be observed across all past generations of lens AF design as a result of the development improvements in mechanics, sensors and algorithms in the camera body. Yes play in the screw-drive mechanisms has been cited as a factor by someone who appeared to be in some level of knowledge. And it is certainly conceivable that design differences of the in-lens drive system mechanical characteristics such as rotational inertia, motor torque, hysteresis (friction) can influence the acceleration, deceleration and concise control of the autofocus performance. Therefore it is reasonable that AF performance may vary somewhat based on the lens AF mechanism design (~ generation) and the highest AF performance may be dependent on use with the latest generation(s) of lens products.
04-09-2021, 09:49 PM - 3 Likes   #67
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One of the biggest things are that system will be able to find a subject, like bird, vehicle, human(and the eye) ect and track it. Then even for lower performance motors(not PLM) it will be a huge advantage and therefore it should make them more fast.

For me, this is a big advantage and I’m looking forward to trying this out with my old lenses too.

But it might be that PLM lenses are waiting to be purchased too...

04-09-2021, 10:48 PM - 1 Like   #68
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I found this PF article on AF drive types. It looks like PLM and SDM are both good for AF-C. PLM is the fastest, and SDM is also fast. In the article it says DC "Not very good at making tiny adjustments and so not perfect for AF.C" Of course Screwdrive comes in last and is poor for AF-C,

The 5 Lens Autofocus Drive Types Explained - Articles and Tips | PentaxForums.com
04-10-2021, 12:30 AM - 4 Likes   #69
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There are many aspects to AF and they are governed by different influencing factors:

  1. x/y-axis 2D tracking of something in the frame (subject pattern recognition and following)
    Pure software and camera processing speed once you have the imaging hardware (= for a DSLR you want a high res metering imaging sensor which we now have with 640x480 pixels) . That is where the K-3 III seems to be a huge step up.
    Lenses irrelevant. Tightly linked to (6).
  2. z-axis prediction (software calculates where the focus plane will be in the near future)
    Pure software and camera processing speed. Will be improved, but already was pretty good.
    Lenses irrelevant
  3. z-axis fast focus adjustment for fast approaching subjects
    Pure lens motor thing. Screwdrives can be very good, IF movement is linear and constant (they have a lot of torque and can turn fast - if the gears are designed to be fast).
    Macro gears are bad. Ring type SDM rules. PLM is similar of lens has small movable elements and so doesnt need a lot of torque.
  4. Precision that drives sharpness
    a) Camera with F2.8 wide sensors defines how precisely the AF logic knows, where it needs to go
    b) gearless lens motors allow moving the lens focus to the desired endpoint. Anything with gears has unwanted "wiggle room". Put a screwdrive lens without quickshift feature on in "AF" mode and try to turn the focus ring. You will be able to do some minor changes and check the effect on a high pixel density camera. That is the bad side of the "wiggle room".
    c) old lenses seem to not have had the hardware to define super precisely where they go. Think of it as similar to the question "how many small steps does a lens know for a 360 degree turn of the focus ring?". If the lens can only report 50 steps then this is less precise than 500 steps.
  5. erratic movement, accelerating and slowing down again and again
    a) you need maximum torque relative to focus lens element weight for this obviously.
    b) this is where the "wiggle room" from gears has worst effects as it adds up (wiggle room x2 for any changes). So DC and screwdrive and old SDM lenses (all with gears) are subpar to PLM and ring type SDMs.
    c) this is connected to (2) prediction smartness of the camera and (6) speed of recalculations in the camera
  6. adjusting to changed situations and how quickly failed focus can be recovered
    Obviously you want the AF system to recalculate the situation as often per second as possible to "rethink". This is purely camera processing power. The K-3 III will top all earlier models by a large margin as it seems to have much quicker processing. Linked to (1).
  7. usability of outer focus points
    Lens thing. Field curvature and focus shift will negatively impact the AF ability to work with close to edge AF points. So both UWA lenses and very old fast lenses will be worst.
If you understand the above, you'll see that your exact scenario will define which lens/camera combo works best and which is worst. As always any over generalizations are plain wrong.

Lens mount:
  • I do not think this can have a lot off influence as KAF4 is mainly about the aperture. A KAF4 aperture will have advantages for high FPS shooting though (spring loaded apertures might not move fast and reliable enough). This may coincide with AF usage scenarios but would be in effect even for manual focus scenarios as well.
  • Obviously mount versions without SDM-contacts are limited to screwdrive with all of the above implications. The negative effect is driven by the drive type though and not the mount type.

Last edited by beholder3; 04-11-2021 at 05:48 AM.
04-10-2021, 01:05 AM - 1 Like   #70
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I think we can disregard the mount itself completely.

KAF2 can mean screwdrive or old SDM, KAF3 can be old SDM but also DC
KAF4 either PLM or new SDM.

Makes little sense IMO. Let's focus (pun intended) on the type of motor.
04-10-2021, 03:13 AM   #71
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QuoteOriginally posted by Tesla Quote
I found this PF article on AF drive types. It looks like PLM and SDM are both good for AF-C. PLM is the fastest, and SDM is also fast. In the article it says DC "Not very good at making tiny adjustments and so not perfect for AF.C" Of course Screwdrive comes in last and is poor for AF-C,

The 5 Lens Autofocus Drive Types Explained - Articles and Tips | PentaxForums.com
It is really tough to say anything global about specific lens types. The DA *55 has SDM but a really long focus throw and a really slow motor and is completely useless for tracking. The 50-135 is only slightly faster. The Pentax DFA 24-70 is also listed as having SDM, but it is a Tamron produced lens and quite a bit faster.

With screw drive, the motor is typically fast enough, the problem is there simply isn't enough precision in the system to keep the lens on track. Lenses like the FA 135 and DA 40 limited are very fast to focus though -- faster than SDM lenses -- I just wouldn't trust them to be accurate in a tracking situation. They still might be decent on a K-3 III, just a decreased hit rate percentage compared to other lenses.
04-10-2021, 07:27 PM - 4 Likes   #72
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QuoteOriginally posted by Rondec Quote
It is really tough to say anything global about specific lens types. The DA *55 has SDM but a really long focus throw and a really slow motor and is completely useless for tracking. The 50-135 is only slightly faster. The Pentax DFA 24-70 is also listed as having SDM, but it is a Tamron produced lens and quite a bit faster.

With screw drive, the motor is typically fast enough, the problem is there simply isn't enough precision in the system to keep the lens on track. Lenses like the FA 135 and DA 40 limited are very fast to focus though -- faster than SDM lenses -- I just wouldn't trust them to be accurate in a tracking situation. They still might be decent on a K-3 III, just a decreased hit rate percentage compared to other lenses.
This is something I would really like to be addressed in a Pentax Forum review. An assessment of how well the new AF system works in both single shot and continuous mode with ideally:
- F/FA-era screwdrive primes
- F/FA-era screwdrive zooms
- DA-era screwdrive primes
- DA-era screwdrive zooms
- Old SDM star lenses
- DC lenses (such at the 20-40 or 16-85)
- PLM lenses (well, it's "lens" at the moment, but anyway, the 55-300 PLM)
- New SDM (DFA50 or 85 at the moment)
- Sigma 18-35 (or another somewhat recent Sigma with a history of AF complaints)

It's a demanding list, so I know it's a lot easier said than done. But if any site has the knowledge to cover this thoroughly, it's Pentax Forums.

I think if it can be demonstrated that the K-3 III is going to give new value to the lenses we already have, it's going to encourage a lot more people to go for it.
04-10-2021, 11:14 PM   #73
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A couple of thoughts:

a) your categories still are too broad. It actually needs to be done lens by lens. DA 40 and DA 100 macro are not comparable.
b) testing all lenses is unrealistic. Since we talk about sports/wildlife applications mainly I would pick 3-4 tele Zooms only. 50-135, 60-250, 150-450, 70-200; bonus 24-70, 70-210
c) for testing you need a robustly repeatable setup of something that moves in tele range. In my mind the best suited thing you could reuse is the motor driven things which transport paper targets on a pistol shooting range to the shooter. These things move at a defined speed in a defined track in a distance that seems fair for photography purposes and are both large enough and offer the AF system enough area. So that is pretty repeatable and results could be compared. All other options require a lot of effort for setup or are not really comparable.
Nowadays the only other option I see would be to use a drone, but that requires at least a second person with very good flying skills to make it fully comparable (exact same path, same speed etc).

And you have to repeat it all for each lens at least 5 times to get minimally statistically robust data. Cameras need to be on a tripod to eliminate effect of user swaying and shaking more or less.
04-11-2021, 08:45 AM   #74
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QuoteOriginally posted by thibs Quote
I think we can disregard the mount itself completely.

KAF2 can mean screwdrive or old SDM, KAF3 can be old SDM but also DC
KAF4 either PLM or new SDM.

Makes little sense IMO. Let's focus (pun intended) on the type of motor.
I agree. For AF-C, the motor and I think the lens weight are the two variables that effect focusing speed and accuracy.


I would also like to see AF-C tests in lens reviews.
04-11-2021, 09:22 AM   #75
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QuoteOriginally posted by thibs Quote
I think we can disregard the mount itself completely.

KAF2 can mean screwdrive or old SDM, KAF3 can be old SDM but also DC
KAF4 either PLM or new SDM.

Makes little sense IMO. Let's focus (pun intended) on the type of motor.
We cannot focus on just the motor.
KAF4 would still be useful to those poor souls who own a K-50 / K-70 and experience "Dark Image Syndrome".
They could use a 55-300mm PLM lens, for example, even though its predecessor would be of little use to them.
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