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02-18-2016, 11:16 PM   #1
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K-1 vs K-3 autofocus system - some hardware and other differences

I was curious, so had a look at the Pentax web site to compare the K-3/K-3 II AF system [SAFOX 11] with the K-1 AF system [SAFOX 12].

It was interesting to see that the K-1 appears to share exactly the same AF and metering chips as the K-3/K-3II. (I guess this technology re-use is one factor in keeping the K-1 affordable).

However there are some notable differences between SAFOX 11 and SAFOX 12, as one can see from the infographic I put together below.



From the K-1 AF features page, Pentax expains the new SAFOX 12 features:
QuoteQuote:
The K-1ís AF frame has been widened to optimize the ease of image composition over a larger 35mm full-frame image field. Thanks to the development of a new SAFOX 12 AF sensor module, its autofocus area is approximately 40 percent wider than a conventional AF frame.* In order to contain a longer optical path required for the expanded AF area within a compact housing, the K-1 features an innovative, efficient optical design in which the incoming light is turned back within the AF module. Thanks to the optimization of the condenser lens, it also provides an increased number of AF sensor points (33 in total)...This new AF sensor module features two reflex mirrors. By reflecting the incoming light flux twice on these mirrors, it provides a longer optical path, while its overall size has been kept nearly identical to that of SAFOX 11.
Cleverly, the extra AF points in SAFOX 12 come about as a result of changing the condenser lens in the AF module, not from using a new chip.

Aside from the design changes mentioned above, SAFOX 12 now seems to lack the diffractive lens present in SAFOX 11 AF module, which is interesting. This lens was there to improve AF precision by correcting CA in the AF unit. Not sure of the impact of this.

But whilst the SAFOX 12 module has lost this diffractive lens, it now seems to have gained an IR cut-off filter, placed directly in front of the AF chip, which SAFOX 11 didn't seem to have.

Also notable is how 'color motion detection' in the K-3/K-3 II has changed to 'shape detection' in the K-1 in the Pentax 'Real-time Scene Analysis System', which:

QuoteQuote:
"analyzes such factors as brightness distribution in the image field, the subjectís primary color and its motion with great accuracy and efficiency. In addition, by adopting a breakthrough artificial intelligence technology called deep learning to its image detection algorithm*, this system assesses each individual scene more accurately, while optimizing the accuracy and performance of the light-metering, exposure-control and autofocus systems ...".
However this 'deep learning' intelligence in SAFOX 12 unfortunately only seems to help the AF if the K-1 exposure mode is set to 'Auto' (not Av, P, TAv etc). In contrast, SAFOX 11 was able to benefit from 'color motion detection' in any exposure mode.

There may be other algorithmic and software changes in the K-1 compared to the K-3/K-3II (eg AF-C settings and other AF customizations), but the web site doesn't document these features very well, and the K-1 manual doesn't appear to be available yet.

02-18-2016, 11:52 PM   #2
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I'd say that it is quite logical to have same elements as SAFOX 11 in 12. Otherwise it would be called DAFOX 1.1 or so.

As seen in picture, diffraction lens have been removed, so they can duplicate optical paths and make those optical paths more effective. Maybe it is also the reason for IR cut-off filter. All in all it might be better upgrade than one might think.
02-18-2016, 11:52 PM - 1 Like   #3
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There's a major change in the way the AF system behaves especially during AF.C tracking. In short, the AF system is now able to confirm focus on any combination of points: https://www.pentaxforums.com/forums/190-pentax-k-1/314349-safox-12-autofocus-...nts-focus.html

I simply cannot emphasize enough the importance of this change. This has the potential to dramatically improve AF tracking performance.

Last edited by bwDraco; 02-19-2016 at 12:00 AM.
02-19-2016, 12:30 AM   #4
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QuoteOriginally posted by bwDraco Quote
There's a major change in the way the AF system behaves especially during AF.C tracking. In short, the AF system is now able to confirm focus on any combination of points: https://www.pentaxforums.com/forums/190-pentax-k-1/314349-safox-12-autofocus-...nts-focus.html

I simply cannot emphasize enough the importance of this change. This has the potential to dramatically improve AF tracking performance.
This


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02-19-2016, 01:01 AM   #5
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well at least they reduced the saturation level in the Prime VI advert, that is progress.

I can only assume that is the mask in front of the separator lens?

Last edited by Digitalis; 02-19-2016 at 01:07 AM.
02-20-2016, 05:20 AM   #6
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Rumors and spec sheets cannot answer all questions before the camera really appears... patience
02-20-2016, 07:00 AM   #7
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I don't know if anyone has noticed this in the specs - **During Live View shooting, this mechanism does not compensate for camera shake caused by horizontally and vertical shift.
Most of my shooting is through the viewfinder but it seems strange that 5 axis IS in not possible in Live View.
02-20-2016, 09:42 PM   #8
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QuoteOriginally posted by rawr Quote
SAFOX 12 now seems to lack the diffractive lens present in SAFOX 11 AF module, which is interesting.
The diffractive lens's function was to avoid (front-) focusing errors based on dispersion effects in the AF module in the presence of red / infrared light.
The new approach to combat this problem (from which the K-5 and earlier Pentax DSLRs suffered) is using an IR cut-off filter and the metering chip. The latter is used to determine colour temperature so that it can be used for compensating focusing errors.

I strongly suspect that the K-1's metering chip is also used to obtain information about the actual magnification of the mounted lens.

The translational aspect of five-axis stabilisation only works well in macro shooting scenarios when the magnification of the lens is known. The magnification, however, when close focusing does not only depend on the focal length but also on the subject distance.

As most Pentax lenses only provide very crude information about the subject distance (focus setting), I'm pretty sure that information from the acceleration sensors is used in combination with analysing image shift from the metering sensor to work out the actual magnification so that the SR can compensate accordingly.

QuoteOriginally posted by screwdriver222 Quote
Most of my shooting is through the viewfinder but it seems strange that 5 axis IS in not possible in Live View.
See my above hypothesis.

It would explain why full five-axis stabilisation doesn't work in live view (as the metering chip does not get any information when the mirror is up).

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