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11-16-2010, 05:14 AM   #31
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QuoteOriginally posted by soalle Quote

Since we are stucked with single tests, maybe a performance indicator considering nearest in-focus distance and 2nd nearest in-focus distance would decrease further the bias.
But the 2nd would typically be 1/fps away, further favouring the faster burst and not helping much. It is exactly as applying NR to an image: you reduce the random variation at the expense of the signal. You just smear. I must say that FNAC seems to have the greatest optical bench for AF measurements but is not exploiting its potential.

QuoteOriginally posted by soalle Quote
Btw, what struck me the most is the same performance for K-r and K-x... very strange since they should have 2 different AF modules...
That's the strongest indicator to date that the Safox IX claim for the K-r may be wrong. The full result looks too similiar, it's not just a measurement alias artefact.

It can be found out though. The AF modules look different if you look at them from within the mirror box, e.g., using a dentist mirror. For K-5 vs. K-7 that is.

11-16-2010, 06:11 AM   #32
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QuoteOriginally posted by falconeye Quote
OTOH, there still is the effect of lens selection which I think is more serious. Using the FA* 80-200/2.8 is an interesting choice. Is it the lens giving the best possible performance for Pentax? Or just some odd accident?
The Samsung GX-20 was tested with an 18-250mm and slightly outperformed the K20D. Of my six DA zooms, I would say the 18-250 has the slowest AF. The K-5 and K-r were tested with a 70-200mm and the K-r tied with the K-x (except more fps). The K-x was tested with the 80-320mm, so perhaps the lens doesn't matter that much for this test.

BTW, when I search under 70-200mm f/2.8 IF ED, the results all come up as Nikon. Could they be using a Nikon lens for the latest Pentax tests?
11-16-2010, 06:37 AM   #33
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Thanks for gathering and sorting all the info.

I saw the thread over at Dpreview : http://forums.**********.com/forums/readflat.asp?forum=1036&thread=36897755

But your run-through is much more thorough
11-16-2010, 08:11 AM   #34
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QuoteOriginally posted by falconeye Quote
JP, I'll give it a try

I assume that AF.C can be characterized by its ability to cope with a change of subject distance. I think that's pretty evident. With a static subject, any AF.C will perform great

Now, assume a 50 km/h vehicle at 1 mile distance: almost static. Next, assume the same vehicle at 10 m distance: dramatic action!

So, counting the number of good images means nothing. As they may all be from the static phase. The moment where the AF.C stops being able to follow the action means everything. And this moment is defined by the nearest sharp image, given that speed, contrast, field of view are all constant.
This is what happens when you are trying to capture a fast moving subject toward you, and the faster it is, the more difficult it is for the AF-C to lock on it.
For instance, BIF ... ! ... or an olympic 100m sprinter.

If you want a measure of the speed which the AF.C can capture, then just take the inverse, like 20m/nearest distance, and you get a relative capturable speed.

What does it mean in practical term?

Well, if I read the graph correctly, in the past Pentax could deal with a speed of "1" where the best managed to deal with "3", three times as fast. Now, it seems the K-5 closed the gap and is in a good average position, like "2". Twice as fast an action as with previous Pentax and in one league with D7000. The best are still 50% faster (at least).
So if the K20D is at 1 and the K5 at 2, does it really mean that the K5 is actually 100% faster?
In practise, an AF.C either follows the action or not. So, in one event the difference may be insignificant where in another, the difference is between win and fail. It really depends on what you shoot. The K-5 can just cope with more situations. And there are still situations no camera of 2010 can deal with.

Moreover, for fast action and long tele, the ability to track the subject (follow a subject with its active focus point) is important too. An ability Pentax still lacks. FNAC did not look into 3D tracking though.
I most often use a DA*300/4 and of course this lens is never quite fast enough, at least with the K7 and certainly not with the K20D. I am hoping this will be better with the K5.
Should we assume that a faster, quality tele/zoom, such as a Sigma or a Tamron 70-200/2.8 would perform better?

Remains that Pentax still does not have a DSLR which can "track" the subject (3D tracking?) and this would mean that they'd have to change their entire AF system, right?

Thanks for your simplified explanation, much appreciated.


11-16-2010, 10:28 AM   #35
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QuoteOriginally posted by audiobomber Quote
The Samsung GX-20 was tested with an 18-250mm
Well spotted

QuoteOriginally posted by audiobomber Quote
The K-5 and K-r were tested with a 70-200mm and the K-r tied with the K-x (except more fps). The K-x was tested with the 80-320mm
That's not true. They are all tested with FA* 80-200/2.8 EF ID (my best guess). Whereever they print 70-200 it is a printing error as it is either is 3rd party (no EF ID) or not 70mm. The copy-paste error of the 70-200mm string is the most likely cause. I don't assume that they changed the lens, except with the GX20. I've seen numerous copy-paste errors, like a reversal of the distance scale

---------- Post added 11-16-10 at 07:40 PM ----------

QuoteOriginally posted by jpzk Quote
So if the K20D is at 1 and the K5 at 2, does it really mean that the K5 is actually 100% faster?
As the lens didn't get faster, the AF measuring part actually would have improved by more than this.

in photome, field 021F AFInfo[7], there is an AF measurement time and you can see rather low values there in good light. I guess this is the AF sensor's exposure time before an AF decision can be computed. Another point is precision: despite the increased exposure time, in low light the sensor delivers inaccurate data and the AF will hunt a little bit.

As for 3D tracking: It basically would require smaller (and more) sensors and an update to the AF prediction algorithm. That's not a complete overhaul of the AF module. I think the actual AF sensors are just a mask and very last CCD chip. To replace this "end part" for another one with smaller and more areas may not be that big a change actually. Of course, you would have to update the AF overlay in the prism housing too.

Last edited by falconeye; 11-16-2010 at 10:41 AM.

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