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04-04-2021, 10:59 AM   #1
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K-3 Mark III - Autofocus at f/8

The K-3 Mark III introduces a greatly-improved autofocus system, SAFOX 13, with a high-density grid and wider frame coverage. But with certain lenses, some or all of the outer points are disabled. Among the lenses affected is the DA 560mm f/5.6, with which only the center grid is available.

But what about autofocus at f/8, e.g. with the DA 1.4x teleconverter attached? Previous Pentax cameras did not disable or limit autofocus functionality in any way with lens/teleconverter combinations slower than f/6.3 (outside of the oddball 1.7x autofocus converter), so I'm wondering if there are limitations with or specific support for autofocus at f/8. Autofocus performance at slower than f/6.3 is, of course, not guaranteed on any Pentax camera thus far, but given that the list of lenses with limited autofocus functionality in the manual (page 117) is subject to change, will we see this with firmware updates (e.g. center point only)?

Draco


Last edited by bwDraco; 04-04-2021 at 02:15 PM.
04-04-2021, 12:39 PM   #2
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Are the outer points actively disabled? Or do they just not work well?

I’ve used lens combos (including the F1.7x converter) that were in the book as “doesn’t work” on other cameras, and they generally don’t work well, but usually they still work if there’s enough light...

If they are actively disabled, I wonder what the threshold is...

-Eric
04-04-2021, 12:55 PM   #3
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The manual says the points are disabled. This is the first time Pentax has done this and it's probably a consequence of the wider coverage of the AF array. This isn't unusual for these sorts of high-density AF systems, but given how Canon does it, I wouldn't be surprised if f/8 autofocus would be impacted in the same manner, possibly in a future firmware version.

Draco

Last edited by bwDraco; 04-04-2021 at 02:15 PM.
04-05-2021, 01:25 AM   #4
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This is not related to a specific camera.
What is the advantage -if any - of an increased number of focus points.? Some writers blame Pentax for having too little a number of focus points- Every time I have used other than singlepoint i have been cofused over the wandering red dot. Is the precision of PDAF the same regardless og brand? I should like to have a narrower mesuring angle on KP spotmetering, the precision isnot overly impressive

04-05-2021, 07:12 AM   #5
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QuoteOriginally posted by niels hansen Quote
This is not related to a specific camera.
What is the advantage -if any - of an increased number of focus points.? Some writers blame Pentax for having too little a number of focus points- Every time I have used other than singlepoint i have been cofused over the wandering red dot. Is the precision of PDAF the same regardless og brand? I should like to have a narrower mesuring angle on KP spotmetering, the precision isnot overly impressive
You've got more data to track moving subjects with.

The AF algorithms did see a significant update in SAFOX 12 (K-1), where an arbitrary combination of points can be indicated as in focus rather than no more than two. Assuming that this remains the case for the K-3 Mark III, the extra points will provide a lot more data, increasing the accuracy of predictive focusing.

Pentax engineers did note that they've essentially redone the AF algorithms in SAFOX 13. Among other things, the AF system retains a longer history of tracking data in memory, and can better cope with erratic motion and sudden changes in velocity. We can't say for sure until more users have had experience with the camera, but I would be very surprised if AF.C performance did not improve significantly.

As for AF at f/8, I don't think the size or number of AF points really matters here.

Draco
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