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09-06-2015, 07:06 PM - 3 Likes   #1
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AF.C behavior of the K-3 II; or, how to make the most of the AF system

After several days of intensive soccer photography, I'd like to provide some notes about the AF.C behavior of the K-3 II.

From what I can tell, the camera uses information from both the 86k pixel RGB metering sensor and the SAFOX 11 AF array. When Expanded Area AF is enabled, autofocus will begin at the selected AF point but distance information from the entire expanded area are used. The camera uses this information to maintain a lock on the subject as it moves, as well as to predict the subject's position at the time the shutter opens (yes, AF.C on the K-3 II is fully predictive!). In the event the lock on the target is lost, it will use this information to make a best-guess determination as to where the correct focus position is and to try to reacquire a lock on the target as quickly as possible. If the lock cannot be reacquired within a certain period of time (determined by the Hold AF Status custom setting—I usually have it set to medium or high), the camera will start over and refocus at the selected point; however, incorrect focus can occur if another subject with similar color patterns appears near the position of the original target within the selected AF area.

As such, if you're dealing with unpredictable fast-moving subjects, using 25-point Expanded Area AF (shown on the top-plate LCD as SEL3) or even 27-point Expanded Area AF (SEL4) allows for fast, reliable focus tracking. However, if the subject is more predictable (eg. swimming, track and field), the 9-point mode (SEL2) is likely to produce better results.

As for the other AF custom settings, I use Auto for both the first and subsequent shots in AF.C continuous shooting (custom functions 16 and 17, respectively). This ensures the camera has a chance to lock onto the target without excessively slowing it down. I get a stable frame rate of about 6.5 fps this way while maintaining reliable focus tracking.

It's a real pleasure to be able to work with Pentax's most advanced AF system. SAFOX 11 and the improved AF.C algorithms in the K-3 II allow for remarkably high keeper rates even for fast, unpredictable subjects like soccer players at high continuous shooting speeds. Ricoh engineers have finally come up with an AF system that is genuinely competitive with C&N. However, there is still much room for improvement: the number and spread of AF points can be increased and the performance of lens AF motors is often lacking. Better concurrent use of all the AF points is still possible, with indication of all of the AF points in focus in the viewfinder.

—DragonLord


Last edited by bwDraco; 09-06-2015 at 09:38 PM.
09-06-2015, 07:21 PM   #2
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What was your hold setting? Update: in the linked article you say 4. Thanks.

There are two situations where I lose shots with the K3. Low contrast subject and or smaller than the focus point. Tracking and shooting high speed continuous, ie. bird in flight, it seems to overwhelm the processing ability and quite a few are out of focus.

I'm curious whether the K3ii is an improvement.
09-06-2015, 08:46 PM   #3
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Thanks for posting this. There seems to be a remarkable lack of real world info on how to use the AF.C options in this camera.
09-07-2015, 02:11 AM   #4
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QuoteOriginally posted by DragonLord Quote
After several days of intensive soccer photography, I'd like to provide some notes about the AF.C behavior of the K-3 II.

From what I can tell, the camera uses information from both the 86k pixel RGB metering sensor and the SAFOX 11 AF array. When Expanded Area AF is enabled, autofocus will begin at the selected AF point but distance information from the entire expanded area are used. The camera uses this information to maintain a lock on the subject as it moves, as well as to predict the subject's position at the time the shutter opens (yes, AF.C on the K-3 II is fully predictive!). In the event the lock on the target is lost, it will use this information to make a best-guess determination as to where the correct focus position is and to try to reacquire a lock on the target as quickly as possible. If the lock cannot be reacquired within a certain period of time (determined by the Hold AF Status custom setting—I usually have it set to medium or high), the camera will start over and refocus at the selected point; however, incorrect focus can occur if another subject with similar color patterns appears near the position of the original target within the selected AF area.

As such, if you're dealing with unpredictable fast-moving subjects, using 25-point Expanded Area AF (shown on the top-plate LCD as SEL3) or even 27-point Expanded Area AF (SEL4) allows for fast, reliable focus tracking. However, if the subject is more predictable (eg. swimming, track and field), the 9-point mode (SEL2) is likely to produce better results.

As for the other AF custom settings, I use Auto for both the first and subsequent shots in AF.C continuous shooting (custom functions 16 and 17, respectively). This ensures the camera has a chance to lock onto the target without excessively slowing it down. I get a stable frame rate of about 6.5 fps this way while maintaining reliable focus tracking.

It's a real pleasure to be able to work with Pentax's most advanced AF system. SAFOX 11 and the improved AF.C algorithms in the K-3 II allow for remarkably high keeper rates even for fast, unpredictable subjects like soccer players at high continuous shooting speeds. Ricoh engineers have finally come up with an AF system that is genuinely competitive with C&N. However, there is still much room for improvement: the number and spread of AF points can be increased and the performance of lens AF motors is often lacking. Better concurrent use of all the AF points is still possible, with indication of all of the AF points in focus in the viewfinder.

—DragonLord
I shoot a lot of swimming and agree with your findings.

It always a trade off Processing power Vs number of point processed

With early low powered Pentaxs (k10d,k20d) only single point was any use and even there often AF-s was more successful
k5 5 point and single point in af-C were very sucsefull
and k3 as you say 9 piont for linear tracking 25/27 for random

I've always found focus point expansion considerably more important when tuning AF-C than hold settings.

Hold settings are useful for known AF misses in linear (in swimming breast stroke ) and also to stop the AF ratcheting when trying to track non linear targets.

In general AF hold setting is more defined by the photographer panning ability when tracking none linear targets than a predefined one size fits all per sport/action

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