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Forum: Pentax K-1 & K-1 II 06-23-2018, 06:06 PM  
The Ugly Truth About Pentax AF-C (Cuteness included)
Posted By photoptimist
Replies: 123
Views: 9,152
Interesting. Here's data on average AFIntegrationTime as a function of EV level posted to a DPR thread (Real World AF Speed Data. K20D and K10D: Pentax SLR Talk Forum: Digital Photography Review) by a "MightyMike" from Canada! The 2009 data set comes from 1176 images all made with a Sigma 24mm F1.8 that MightyMike said was one of his slowest-focusing lenses.

These were all from photos that had a near full or very high battery charge
EV0 = 250ms (average AF Integration Time)
EV1 = 197ms
EV2 = 181ms
EV3 = 194ms
EV4 = 164ms
EV5 = 103ms
EV6 = 63ms
EV7 = 27ms
EV8 = 28ms
EV9 = 11ms
EV10 = 17ms
EV11 = 16ms
EV12 = 13ms
EV13 = 0ms
EV14 = 0ms
EV15 = 250ms

these are from photos that had a low battery charge (much lower sampling
EV3 = 219ms (good charge = 194ms)
EV4 = 221ms (good charge = 164ms)
EV5 = 140ms (good charge = 103ms)
EV6 = 92ms (good charge = 63ms)
EV7 = 78ms (good charge = 27ms)
EV8 = 24ms (good charge = 28ms) not a typo
EV9 = 25ms (good charge = 11ms)
There's a strong relationship between EV and AFIntegrationTime but there's also scatter in the data which could reflect "black-dog in sunshine" effects or low-contrast scenes or who knows what.
Forum: Pentax K-1 & K-1 II 06-23-2018, 03:26 PM  
The Ugly Truth About Pentax AF-C (Cuteness included)
Posted By photoptimist
Replies: 123
Views: 9,152
The various online discussions I've seen all suggest that small values occur in bright sun and large values occur in dim light.

The AF module uses a photodiode array and in dim light (or with lenses with narrower wide-open apertures), those photodiodes take a little longer to gather a sufficient signal. You mentioned that the 1/2000 second shutter speed was not fast enough to stop motion of the dogs and that same blurring issue would affect the AF module.
Forum: Pentax K-1 & K-1 II 06-23-2018, 03:02 PM  
The Ugly Truth About Pentax AF-C (Cuteness included)
Posted By photoptimist
Replies: 123
Views: 9,152
It's called AFIntegrationTime and seems to be an 8-bit integer recording the time in msec (although values of less than 2 msec recorded as zero).

See ExifTool | Pentax Tag Reference | AFInfo Tags
Forum: Pentax K-1 & K-1 II 06-23-2018, 01:39 PM  
The Ugly Truth About Pentax AF-C (Cuteness included)
Posted By photoptimist
Replies: 123
Views: 9,152
Interesting test, but......

The AF system also has an operating shutter speed that is linked to the aperture of the lens and brightness of the scene (it's in the EXIF data if you care to look). It's quite possible that AF array readings on the rapidly rippling fur, flying dogs, rapid panning, and rapid zooming were simply too blurry for the AF system to read sufficient detail.

SEL25 AF Mode does not make sense because that's a Live View mode which is a particularly slow way to AF. I assume you meant one of the Expanded Area AF modes but then it's possible that the AF system was locking more often that you thought but locking on to more AF-friendly parts of the scene (i.e., not the blurry dogs).

Finally, normhead is right. Without a side-by-side comparison of keeper rates from another shooter with the same lens but another camera brand, there's no way to tell if Pentax AF is ugly or beautiful.
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