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11-09-2013, 11:54 AM   #1
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K-3 AF Testing

I finally had some time to do some testing of the AF on the K-3.

Method: Using Spyder LensCal, set on a tabletop tripod and leveled. Camera on a tripod and also leveled and aligned as closely as possible to perpendicular of the target. Distance was 40 inches (100cm). I did not move the camera for different lenses. All lenses were used at their widest aperture. Quickshift lenses were set to infinity by hand and then auto-focused on the target, non-quickshift lenses were focused on my hand about 12 inches from the lens front and then auto-focused on the target. AF was in 9 point auto. SR turned off. Test was repeated 4 times and results noted. Lighting was bright office light using daylight corrected fluorescent bulbs. Images were imported into Lightroom 5 and clarity of +90 added to make the numbers stand out.

Results:
  • Pentax F 50mm f/1.7 -0-
  • Pentax F 28mm f/2.8 -0-
  • Pentax DA 21mm f/3.2 -0-
  • Pentax DA 40mm f/2.8 -0-
  • Pentax DA 70mm f/2.4 -0-
  • Pentax DFA 100mm f/2.8 WR -0-
  • Pentax DA 12-24 f/4 @24mm -0-
  • Pentax DA*16-50 f/2.8 @50mm -1
  • Pentax DA*60-250 f/4 @60mm -1
  • Pentax F 35-70 f/3.5-4.5 @70mm -0-
  • Pentax FA 28-70 f/4 @70mm -0-


Notes:
  • The screw drive lenses all locked in quickly and surely, the SDM lenses a little slower with some back & forth. I don't think the behavior is any different than on earlier models. The screw drive seemed faster than on the k-5, but that might just be perception, I have no way to test.
  • The DA*60-250 was by far the slowest to focus. Since it was tested @ 60mm I'm not sure if the results will be any different at the more used 250mm
  • The DA 40 Ltd was by far the most inconsistent, with readings @ -1, -.5, 0, +1, and +.5. They averaged out so no adjustment was made but this behavior was different than the other lenses which were all very consistent through different focusings.
  • The DFA 100mm f/2.8 WR showed a slight back focus but smaller than the ability of the tuning to adjust. I would say +.5 would work but the smallest adjustment would be +1 so I left it alone.
  • The wide angle lenses (DA 21mm, F 28mm, DA 12-24) have such a wide depth of focus that the results were inconclusive but I saw no indication that an adjustment would be needed.
  • The -1 results above are the adjustment I made, the lenses were actually front focusing.
Conclusion:
I am delighted with the k-3's AF ability, I did make an adjustment to the two SDM lenses, but to be honest most people would not be bothered by the difference a -1 adjustment will make. All of the other lenses performed spot on with hardly any variability (except the DA 40mm) between tests. Conditions were of course controlled and only one type of lighting was tested. However, I think this shows the AF in the k-3 (at least my sample) is accurate, fast, and reliable.

11-09-2013, 12:13 PM   #2
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This is good news, and I like your testing methods. I may do the same with my several lenses when my K-3 gets here next week, but it sounds like it's pretty close with just about everything.

John
11-09-2013, 12:21 PM   #3
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QuoteOriginally posted by jatrax Quote
Camera on a tripod and also leveled and aligned as closely as possible to perpendicular of the target. Distance was 40 inches (100cm).
QuoteOriginally posted by jatrax Quote
The DA*60-250 was by far the slowest to focus. Since it was tested @ 60mm I'm not sure if the results will be any different at the more used 250mm
Considering the minimum focusing distance of the 60-250 is 110cm (43.2 inch), the slow focus was maybe because it was at the edge of the possibility of the lens to focus so close. Hence the slow speed, maybe ?

(the lens review page : SMC Pentax-DA* 60-250mm F4 ED [IF] SDM Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database )

Anyway. I won't say "thank you for this test", because now i have to get this wonderful beast that is the K3, and geez, this will empty my bank account !
11-09-2013, 12:32 PM   #4
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When I tested 35/2.4 AF on my K-30, it was far more critical at infinity (trees on the horizon) than anything indoors. Just saying.

11-09-2013, 12:40 PM   #5
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QuoteOriginally posted by aurele Quote
Considering the minimum focusing distance of the 60-250 is 110cm (43.2 inch), the slow focus was maybe because it was at the edge of the possibility of the lens to focus so close. Hence the slow speed, maybe ?
Quite possible, I will need to retest. I was setup in my (small) studio and just did not have the room to really back up.
11-09-2013, 02:43 PM   #6
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QuoteOriginally posted by jatrax Quote
Quite possible, I will need to retest. I was setup in my (small) studio and just did not have the room to really back up.
what you did is great ! i was just wondering why the 60-250 was slow, as it shouldn't be that slow, and i saw the distance of the charts and i started wondering...

Anyway, i think what the other lenses did show is that the new AF is far more accurate and consistent !
11-10-2013, 09:17 AM   #7
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QuoteOriginally posted by aurele Quote
Anyway, i think what the other lenses did show is that the new AF is far more accurate and consistent !
Yeah, the k-5 took a bit of adjustment with most lenses. I am astonished that with the variety of lenses I tried (F,FA,DA,DA*) that all were essentially accurate. It's also odd that the only ones off were SDM. But this test was a small sample, will be interested in seeing what others find.

We had all those theories about the lens being off a bit and the camera being off a bit and if those differences matched you had a 'good' lens and if not you had a 'bad' lens. And now all of those lenses that were not perfect on the k-5 are suddenly 'good' lenses? Whatever they did a big thank you to Ricoh for the AF system!
11-10-2013, 10:00 AM - 1 Like   #8
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QuoteOriginally posted by jatrax Quote
We had all those theories about the lens being off a bit and the camera being off a bit and if those differences matched you had a 'good' lens and if not you had a 'bad' lens. And now all of those lenses that were not perfect on the k-5 are suddenly 'good' lenses? Whatever they did a big thank you to Ricoh for the AF system!
It shows to nay sayers that Ricoh is probably the best thing that happened to Pentax for the last 10 years

11-13-2013, 10:59 AM   #9
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I'm curious if the focus is still stop on in different light. The OP calibrated in daylight corrected fluorescent bulbs. I had AF fine adjusted my DA70 on my K-3 to about a +2 to correct for a slight back focus. I did this in tungsten light at close to minimum focusing distance. But later I took some photos in daylight at about 20 feet, and they pictures looks slightly front focused. I'm not sure if it's due to the different light, or the focus distance, or both. Anyone check focus accuracy with different light sources and/or different distances?
11-13-2013, 02:42 PM   #10
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QuoteOriginally posted by devorama Quote
Anyone check focus accuracy with different light sources and/or different distances?
I formally tested the K-3 in daylight and tungsten light with a few lenses, but only at closer distances. Every lens tested was dead on.

I have not tested at long distances under tungsten light, but long distance is more forgiving, It's close up that DOF is shallow. I haven't formally tested at long range in daylight, but I've shot enough photos to say there's no change, my lenses are perfectly calibrated.

NOTE: I only have one lens that needs adjustment. If I buy a lens and calibration is off, I return it to Pentax under warranty, with a camera. They send it back properly calibrated. My tests thus far show my new K-3 is calibrated exactly like my K20D and (now sold) K-x. The K-5 I bought was perfectly calibrated under daylight, but had severe front focus in tungsten, so I returned it.
11-13-2013, 05:21 PM   #11
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QuoteOriginally posted by audiobomber Quote
...
NOTE: I only have one lens that needs adjustment. If I buy a lens and calibration is off, I return it to Pentax under warranty, with a camera. They send it back properly calibrated. My tests thus far show my new K-3 is calibrated exactly like my K20D and (now sold) K-x. The K-5 I bought was perfectly calibrated under daylight, but had severe front focus in tungsten, so I returned it.
I take this to mean that Pentax perform perfect calibration of the lens for your particular body. But what happens when you obtain another body, especially if you still retain the one used for the calibration?
11-13-2013, 06:46 PM   #12
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QuoteOriginally posted by bxf Quote
I take this to mean that Pentax perform perfect calibration of the lens for your particular body. But what happens when you obtain another body, especially if you still retain the one used for the calibration?
As I said, my K-3 is dead accurate with all the lenses that were calibrated to my K20D, so I didn't need to do anything. At worst I would have had to do a global adjustment to the K-3.
11-13-2013, 07:04 PM   #13
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QuoteOriginally posted by bxf Quote
But what happens when you obtain another body
Every body and lens is essentially unique in the way it is manufactured, when you are talking very fine tolerances. Put any of the two items together (lens on body) and you will get a unique combination, kind of like a lock and a key.

For example I have a Tamron lens (A) on my K-5 that requires about -9 AF adjust, but the same lens is perfect on the K-x. I then put another Tamron lens (B) on both the K-5 and the K-x, and that lens is perfect on both bodies. When I get my K-3, who knows what the story will be when I mount either (A) or (B). Both could be perfect, or (B) may require adjustment and (A) may not. Within bounds, this stuff is normal.
11-14-2013, 08:29 AM   #14
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QuoteOriginally posted by audiobomber Quote
As I said, my K-3 is dead accurate with all the lenses that were calibrated to my K20D, so I didn't need to do anything. At worst I would have had to do a global adjustment to the K-3.
Hi Audiobomber,

Are you saying that when you send the lenses and camera body that;

a) the lenses come back calibrated to the camera body?

OR

b) The autofocus fine adjustment of the body has been tweaked for all of your lenses?

This is of great interest to me as the K3 jpeg EXIF data isn't properly recognised by FocusTune 2.0 or 3.0 Goldbeta and I definitely need to get my lenses calibrated to my K3.

What I find confusing is that if they have been calibrated to one body you seem to imply that this calibration is valid for the next body you get (less the tungsten lighting issue). If this is so then this implies that the camera bodies are not a significant variable in lens to sensor focusing distance. This is strange to me as my k5 and k5iis needed different AF fine adjustment for the same lenses. Unless of course the difference lies in the actual increments of AF Fine Adjustment deployed by different models. However this would seem unlikely.

Any thoughts on this?
11-14-2013, 08:59 AM   #15
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I had my DA*300 sent in with my k-5 a while ago, mechanical issues with the lens so I sent both.
The 300mms is calibrated on my new k3. This is Pentax Canada. They seemed to do their magic on both the lens and body.
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