What is the best m43 for focus tracking?

Started Mar 31, 2013 | Questions thread
Anders W
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Re: what is the best m43 for focus tracking?
In reply to amtberg, Apr 4, 2013

amtberg wrote:

Anders W wrote:

amtberg wrote:

Anders W wrote:

Second, I have excluded the results for the Olympus E-PM2 and E-M5 since the results indicate that the lab made the mistake of shooting both cameras in high-speed burst mode where they won't even try to AF between shots. The buffer has then filled rapidly, which explains the slow rate at the end of the series.

Seems like you disregard the bad result for two  cameras while ignoring a related problem in this whole test.  It wasn't just the EM5 and EPM2 where bad settings/buffer size affected the results.  Many of the cameras apparently ran out of buffer before closest approach.

What would the examples be and how do you deduce that they did?

I think that is giving some of the DSLR's artificially bad results.  And in general, the results are not as fine-grained as the numbers suggest insofar as there seems to be a +/- difference of at least 3-4m depending on when the burst was started and thus when the last exposure was snapped in relation to the object distance.

Again, on what basis do you draw that conclusion? Just want to hear how you reason before saying what I think about it.

More generally, there may well be a margin of error of the kind you suggest (although I'd say it is hard to tell how big it is) which is why I suggest looking at the broader pattern and not pay too much attention to the results for each individual camera. Preferrably, they should have run this test a number of times per camera and reported the mean as well as standard deviations.

But this is about the only systematic AF-C test that I have been able to come up with and I think that, if interpreted in terms of broader patterns, it does tell us something. Let me know if you or anyone else has a better data source.

I'm just looking at their diagrams showing when the photos were taken in relation to the proximity of the approaching focus target.  In many cases, especially with the DSLRs, the buffer seems to have filled up before the target got very close, so the frequency of pics slowed down.  If the last pic in the series was snapped at 20m, that's obviously not going to be an accurate reflection of that camera's C-AF performance.  Look at the Sony A77, for example.  The buffer ran out at about 19m, then one more pic was taken at about 15'.  Could it have AFd at 5'?  Who knows?  In the case of the 5D, the closest shot attempted was at about 8.5m.  With the 600D no pics were taken inside of 11m.

First, note that the reason why I excluded the results for the E-M5 and the E-PM2 was not that their buffers filled. As I pointed out from the outset, the reason that I excluded them is that they were shot in a burst mode where they won't even attempt to AF except for the first shot in the burst. This in turn means that the test doesn't, for these two cameras, test what it purports to test.

Second, note that the test is a joint test of AF-C and burst-mode (including buffer) capabilities, and that the outcome is measured in two different regards: Number of sharp shots and subject distance for the last sharp shot. These preconditions are the same for all cameras tested, whether mirrorless or DSLR. Further, if some of them do worse when it comes to subject distance because their buffer filled as a result of high fps, they are likely to do better with regard to the number of sharp shots fired than they would if the fps had been lower and the buffer never filled.

Third, I went through the entire set of cameras looking for instances where it seemed likely that the camera had been hampered at the end due to the buffer being fill. I found only two likely candidates: the Samsung NX1000 on the mirrorless side and the A77 on the DSLR side.

Fourth, you cannot assume, as you seem to do, that a lower fps at the very end is always due to a buffer-full condition being reached. As you approach the end of the test, it gets more and more difficult for the AF system to keep up, i.e., keep the subject in focus. As you know, the distance the AF mechanism has to travel for every meter the subject distance shortens is much, much larger at the end of the test than at the beginning. There are two different ways for the camera to handle that predicament: It can keep up the fps at the risk of the shots being unsharp or it can try firing at a slower rate or stop firing alltogether when it finds that it doesn't make sense to do so. As the results show, different cameras are programmed to behave in different ways here: Some keep firing but fire unsharp shots and others slow down or stop firing altogether.

In every case the closest attempt depends entirely on the timing of the burst.  So, for example, with the Nikon D800 the last pic was snapped at 4.5m and the second to last at 8m.  What if the last shot had been at 6m instead of 4.5m?  Might it have been in focus?  Maybe....

While there might well be a stochastic element involved here, which is why I prefer to look at these data in a statistical way, you strongly exaggerate that element when you claim that the closest attempt depends entirely on the timing of the burst. What we know in the case of the D800 is that its true result is somewhere between 8 and 4.5 m. I prefer to record, for this camera as for others, the last sharp shot. In this case, the result of 8 m is still sufficiently good to place the D800 towards the top end of the distribution. If all cameras had reacted by firing one or more unsharp photos at the end, an alternative method would have been to record a point mid-way between the last sharp shot and the next one. But since some cameras quit firing instead of firing unsharp shots, that method cannot be used across the board.

If the GX1's buffer had been started a hair later might not have taken that list pic and it could have scored an 8 instead of a 2.

The remarkable thing about the GX1 shot at two meters is not that it was fired but that it was sharp. The D4, D800, and D600 fire at pretty short distances too, but the shots they fire are no longer sharp.

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