[falconeye]

This is rare and good news for Pentax:

Pentax wins (sort of) a comparative AF test executed by German magazine ColorFoto, as reported in issue 09/2011 in hands now by subscribers to the magazine.

The cameras participating in the test have been:

• Phase AF (in order of respective accuracy, best is first):
  
  Pentax K-5
  Sony Alpha A55
  Canon 7D
  Nikon D7000
  .
• Contrast AF (in order of respective accuracy, best is first):
  
  Panasonic GH1
  Olympus

The headline reads:

The phase AF fraction surprises with an outsider being their number one: Pentax focusses most accurately, ahead of Sony and even Olympus (contrast AF).

The original report is from vordprefect on German forum DFN -> DigitalFotoNetz.de :: Thema anzeigen - Pentax (K5) stellt am besten scharf!

The original report contains a few benchmark figures too. I'll report more on the results as soon as I find a copy.

Or maybe froeschle does, as he knows the same (or more) as I do about this.

Some preliminary remarks:

1. German magazine ColorFoto is ok, not in one league with Chasseur d'Images but some of their tests do make sense. ColorFoto is the leading printed photo magazine in Germany too. The AF test is their September cover story.
2. I measured AF accuracy myself. This is not easy and very dependent on the sample (if not fine tuned for AF accuracy) and the lens. The statistical fluctuation is significant too. So, I need to look into the test to judge if it makes sense or not. In some of my tests with spot-on AF calibration, K-5 phase AF could beat K-5 contrast AF. But in some of the tests only.
3. The emphasis on accuracy rather then mere speed is a good sign that the media respond the the ever increasing challenge to focus high resolution APS-C cameras.

Anyway, this is another bold win for the Pentax K-5. The cover of the magazine is here:
- Heftvorschau AUDIO - colorfoto - Magnus.de


EDIT Sep 6, 2012:
The test report is now online:
-> www.colorfoto.de/testbericht/7/7/6/2/0/2/Test_Autofokus_ColorFoto_2011-09.pdf

---

Last edited by falconeye; 09-06-2012 at 12:54 AM.

[johnmflores]

Nice find and even nicer result! Thanks for sharing.

But really, would it kill a publisher to put the K-5 on the cover if it wins the headline story contest?

[falconeye]

Nice find and even nicer result! Thanks for sharing.

But really, would it kill a publisher to put the K-5 on the cover if it wins the headline story contest?

Maybe?
As it stands, all Canikon shooters buy the issue to see if they've beaten Nicanon. Only to find out after reading that they all lost against Pentax. Not a bad way to tell the story too. Not bad at all

But to be fair, the winner of the cover story is Panasonic. Pentax was #2 and only winner within the phase AF camp.

BTW, the cover was the result of a user poll on their website:

(the actual cover is on the left side)
cf. ColorFoto Titelwahl - Mitmachen und Gewinnen - colorfoto - Magnus.de

Only two options and both had Canikon on the cover. One title said "AF: 30% blurred". A majority opted for the AF test to be the cover story over the portrait workshop.

[RonHendriks1966]

That is nice. Well it also depends on the lens you use I guess. It locks in good is my experience too.

[Kenn100D]

This would be nice at the back of the front cover. Hopefully Pentax Change this to K-5 and K-r.
"....Other than the Big Two"

[froeschle]

Or maybe froeschle does, as he knows the same (or more) as I do about this.

I can scan it tomorrow and forward it to you . I just had a short look at it. Some findings are imho disputable as well as the final comment is. Canon and Nikon are bottom of the league with Pentax being the leader in the phase AF fraction.

[falconeye]

Maybe, I prepare the discussion by a measurement I posted in the Silver K-5 thread some time ago (comment shortened):

I attach a chart of measured blur (~defocus) vs. AF calibration for the DA70 Ltd. at f/2.4. For two different samples of the K-5 camera and at daylight.

As one can see, one sample needs about -10 while the other about -1.5. However, within an interval [-6, +2], I would have a hard time to prefer any value above another, using visual inspection. The performance is almost the same.

The best values achieved by one sample at 0 AF fine tuning (1.88px remaining edge blur) were almost perfect (1.85px at -2 was the optimum for this lens and aperture, only beaten at smaller apertures, like, e.g., 1.59px). 1.25px is an ideal lens in my setup.

Contrast AF (with the aperture as in the chart) performed worse (about 2.3px) but remained consistent across samples.

So yes, K-5 phase AF can be very accurate but its accuracy is a fragile beast

I'll look into the test with this experience in mind.

[Kenn100D]

@Falk,

Just want to ask regarding K-5 phase AF being very accurate...

Does it mean that Phase AF of K-5 being accurate is dependent on how the lens was calibrated from production?

[froeschle]

To continue, the very first article in the magazine is devoted to Ricoh buying Pentax. The verdict is that this change primarily will have a positive impact.

Lens wise, the DA 16-45 got a recommendation, the DA* 16-50 was criticized.

[falconeye]

Does it mean that Phase AF of K-5 being accurate is dependent on how the lens was calibrated from production?

Frankly, I don't know.
Theoretically, a lens shouldn't have to be calibrated as much as the body. Because the AF module anyway sees any defocus.
But I didn't systematically check it.
From two K-5 bodies and two lenses (FA31 and DA70, i.e., four combinations) I'd say that there is significant sample variation between bodies and some bodies need less AF correction than others. When needing less AF correction, K-5 phase AF often beats contrast AF accuracy. With the lens being the smaller factor. But not always.

The best focus I achieved at 31mm at f/5.0 was 1.35px with contrast AF while the two best phase AF measurements I got were 1.24px (which is a fabulous value) and 1.45px. That's all in one ball park.

I don't have enough data to isolate factors which make phase AF the option to go for. I am sorry.

But let me say this much (which is the safe variant of statement I can make):

With the K-5, phase AF can be more accurate than contrast AF. But the performance is more fragile and in other cases, contrast AF may win because it delivers a more stable accuracy (more stable across bodies, lenses and apertures). OTOH, contrast AF can fail miserably and fortunately by so much that it is visible to the naked eye.

Note that the above is a non trivial statement. Many testers assume that Contrast AF or Manual LV focus is the way to go for tests. Not necessarily so though with the K-5.


Note:
I said several times that I consider mechanical focus precision, in particular a play (or better its absence) between the forward and backward focus direction, to be crucial for accurate focus. At least for focus algorithms which go forth and back. Most contrast AF algorithms do it while it can be avoided in many cases for phase AF. But better contrast AF algorithms (better than Pentax uses) can avoid this too, I worked on them. So, if a lens lacks mechanical precision engineering, it may face some focus accuracy problems for reasons other than optical. So, the build quality may actually pay off here. After all, top notch focus accuracy is much better than the thickness of a hair.

[Class A]

Thanks for sharing Falk!

The numbers look a bit too good in favour of Pentax to be true:

Camera	% sharp	% acceptable	% not sharp
Pentax K5	62,4%	28,9%	8,6%
Sony Alpha 55	62,1%	16,4%	21,4%
Canon 7D	40,2%	29,7%	30%
Nikon D7000	35,2%	40%	24,8%

Source: vordprefect's post @ DFN.

The difference between the K-5 and the D7000 in the above numbers is quite dramatic.

[hawk1500]

Yeah, sorry, I find this a little hard to believe. But whatever, a win is a win. Wonder how many angry letters they'll get from the other camps.

I do like how the cover was STILL of the two usual brands though.

[thibs]

Just curious, those having difficulties to doubt this, do you own a K5 ?
This is really curiosity, I do not own a K5 and I doubt it as well, so really this is no defiance
Just'd like to know...

[froeschle]

They performed about 1300 measurements with 57 lenses on nine cameras.
10 shots using AF were taken in wide/standard/tele position with each lens.
Another picture using manual focus with optimal resolution is the reference.
The ratio of the resolutions of the pictures then serves as a measure.
Lenses used on the cameras:

Canon 7D

Canon 14/2.8
Canon 10-22/3.5-5.6
Sigma 10-20/3.5
Sigma 8-16/4.5-5.6
Tamron 70-300/4-5.6
Sigma 70-300/4-5.6
Canon 70-300/4-5.6
Tamron 70-200/2.8
Canon 70-200/4
Canon 70-200/2.8 (-)
Sigma 18-250/3.5-6.3 (-)
Sigma 85/1.4
Tamron 60/2
Sigma 50/1.4
Canon 24/1.4
Canon 16-35/2.8
Tokina 12-24/4 (-)

Nikon D 7000

Sigma 10-20/3.5
Tamron 70-200/2.8
Nikon 70-200/2.8
Nikon 28-300/3.5-5.6
Sigma 18-250/3.5-6.3
Sigma 70-200/2.8
Sigma 85/1.4
Nikon 85/1.4
Tamron 60/2
Nikon 24-120/4
Tokina 12-24/4

Pentax K5

Pentax 21/3.2
Pentax 15/4
Pentax 14/2.8
Sigma 10-20/3.5
Sigma 70-300/4-5.6
Pentax 50-200/4-5.6
Sigma 18-250/3.5-6.3
Pentax 55/1.4 (The Pentax performs better/more consistent than the Sigma)
Sigma 50/1.4
Pentax 12-24/4

Sony A55

Sony 20/2.8
Sigma 10-20/3.5
Sigma 8-16/4.5-5.6
Sony 70-200/2.8 (-)
Sony 55-200/4-5.6
Tamron 60/2

Contrast AF is the declared winner (and not Pentax within the phase AF group). Furthermore, in the comment, it is proposed to fully skip movable mirrors in digital cameras in the future.

[kanzlr]

A majority opted for the AF test to be the cover story over the portrait workshop.

this quote alone tells you that there is something wrong with a lot of hobbiests priorities.