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04-06-2014, 11:29 AM   #1
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K-3 AF Speed, SDM, and Burst FPS Rate

RE: K-3 and K-5, DA* 16-50, 50-135, and 300.

Just some thoughts on using SDM lenses, AF speed, and burst rate. I've been testing my SDM lenses on my K-5 and K-3 and I've noticed that when set to AF.S the AF speed is very quick and the burst rate is very high, especially on the K-3. However, in AF.C mode both the AF and burst rate slow way down. I wonder if the drain on the battery (I'm using a grip so I have two batteries although they're not in series) is causing the slow down. In any case trying to shoot a moving target becomes problematic in AF.C mode.

I've also read the interview with the CEO of Sigma and his remarks that Pentax is using a mechanical method of AF which is why they are not producing many lenses in the K mount. Now I'm wondering if this is why the Pentax's AF seems slower than the competition and if this is contributing to a higher failure rate in SDM lenses. Is Pentax's desire to keep backward compatibility with its legacy AF lenses preventing it from improving AF speed and lens reliability?

Any thoughts?

04-06-2014, 11:47 AM   #2
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First off, depending on the settings, your AF-C mode can be set for focus priority, meaning it will not fire unless it has focus, this can bring the camera to far less than 1 FPS. Also the AF-S can be set for the opposite which is FPS priority. Check your settings.

And the comment from the sigma CEO was regarding aperture coupling being mechanical, not AF system. But it has to be taken with a grain of salt since almost all lens mount still use mechanical aperture coupling. But Pentax ONLY offers mechanical coupling on K mount, where others support both mechanical and electrical.

Pentax AF system is slower than others and it's a combination of factors, different focussing engine, painfully slow SDM lenses and often lenses not optimized for AF. My fastest AF lens is a Sigma rebrand (quantaray), this thing is blazing fast on AF but manual focus suffers a lot, from close focus to infinity, there is barely 70 degrees movement of the focus ring, making manual focus pretty much useless.

But regarding focus speed, where Pentax falls behind IMO is on tracking objects. I'm not software engineer or camera expert but this is more software and processor related than actual physical equipment. Pentax screw drive lenses move just as fast as any other. Focus and tracking calculation are slower.

Last edited by fgaudet; 04-06-2014 at 11:52 AM.
04-06-2014, 11:57 AM   #3
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QuoteOriginally posted by fgaudet Quote
I'm not software engineer or camera expert but this is more software and processor related
...that and patents. Pentax is not the only brand that is not up to the same performance one might get from the Nikon product.


Steve
04-06-2014, 01:15 PM   #4
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I have been trying to photograph birds flying around and sometimes the tracking is spot on and the keeper rate is pretty high but if the DA*300 misses it takes ages to get the subject back in focus if ever. Doing the same with cars the keeper rate is much higher, larger subjects i guess. I have set the AF-C to focus priority so the frame rate follows the focusing i.e slower with birds than with cars. I have not felt that the SDM slows down in AF-C

What I have noticed is that sometimes the AF-C stops after a while and blinks "out of focus" but it still keeps on shooting and won't retarget and I have to press the button again to "start it up". Is this only me or am I missing a setting? C-18 set to OFF or High does not matter.

EDIT:

Also It starts shooting even if focus priority for first frame is choosen and if out of focus. I now tested this and find that when way out of focus in AF-C you can't just press all the way. First find focus, then shoot. In AF-S you can push all the way and it starts shooting when in focus for the first shot.


Last edited by Tjompen1968; 04-06-2014 at 01:25 PM.
04-06-2014, 03:48 PM   #5
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AF-C is slower than AF-S, in my cameras too. K5-K5IIs. And SDM is slower than Sigma HSM, for sure. So, this behavior is normal. Anyway, no AF system from any manufacturer is 100% full proof, not at the price you pay for a Pentax. You have to learn this behavior, to know what to do in the future. And, maybe to change from SDM lenses, to other, faster lenses.
04-06-2014, 03:51 PM   #6
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QuoteOriginally posted by wtlwdwgn Quote
RE: K-3 and K-5, DA* 16-50, 50-135, and 300.

Just some thoughts on using SDM lenses, AF speed, and burst rate. I've been testing my SDM lenses on my K-5 and K-3 and I've noticed that when set to AF.S the AF speed is very quick and the burst rate is very high, especially on the K-3. However, in AF.C mode both the AF and burst rate slow way down. I wonder if the drain on the battery (I'm using a grip so I have two batteries although they're not in series) is causing the slow down. In any case trying to shoot a moving target becomes problematic in AF.C mode.

I've also read the interview with the CEO of Sigma and his remarks that Pentax is using a mechanical method of AF which is why they are not producing many lenses in the K mount. Now I'm wondering if this is why the Pentax's AF seems slower than the competition and if this is contributing to a higher failure rate in SDM lenses. Is Pentax's desire to keep backward compatibility with its legacy AF lenses preventing it from improving AF speed and lens reliability?

Any thoughts?
Set your body up to back button focus. You press the AF button to focus, not the half shutter. This allows you to have AFS in AFC mode; you just let go of the button. Same when you have focus on a subject, you just shoot without the constant refocus calculations and time.

It took me a couple weeks to train my hand to press the AF button to focus rather than the shutter.
04-06-2014, 04:13 PM   #7
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Some good thoughts. Thanks for the feedback and suggestions.
04-06-2014, 05:02 PM   #8
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I haven't noticed any AF-C slowdown. Using a fast focusing lens like the Sigma 70-200 HSM II (in combination with fast UHS-1 SD cards) I'd be hard pressed to notice any difference between using AF-S or AF-C.

AF area settings, and focus priority settings will likely have a great impact on AF-C speed. Not to mention always be aware of the relatively small size of the whole AF frame of the K-3 when tracking moving targets. If the subject isn't in the box, the AF will not be able to do it's job efficiently. Pic below related.

It would certainly be nice for AF-C tracking purposes to have those AF points spread out further to cover more of the frame. Which would, in turn, probably require more AF points in the camera too



04-06-2014, 05:09 PM   #9
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QuoteOriginally posted by rawr Quote
It would certainly be nice for AF-C tracking purposes to have those AF points spread out to cover more of the frame.
And have customizable grouping options for the auto-focus points

---------- Post added 04-06-14 at 20:15 ----------

QuoteOriginally posted by rawr Quote
It would certainly be nice for AF-C tracking purposes to have those AF points spread out to cover more of the frame.
And have customizable grouping options for the auto-focus points
04-07-2014, 04:48 AM   #10
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QuoteOriginally posted by Tjompen1968 Quote
I have been trying to photograph birds flying around and sometimes the tracking is spot on and the keeper rate is pretty high but if the DA*300 misses it takes ages to get the subject back in focus if ever. Doing the same with cars the keeper rate is much higher, larger subjects i guess. I have set the AF-C to focus priority so the frame rate follows the focusing i.e slower with birds than with cars. I have not felt that the SDM slows down in AF-C

What I have noticed is that sometimes the AF-C stops after a while and blinks "out of focus" but it still keeps on shooting and won't retarget and I have to press the button again to "start it up". Is this only me or am I missing a setting? C-18 set to OFF or High does not matter.

EDIT:

Also It starts shooting even if focus priority for first frame is choosen and if out of focus. I now tested this and find that when way out of focus in AF-C you can't just press all the way. First find focus, then shoot. In AF-S you can push all the way and it starts shooting when in focus for the first shot.
Sounds like you have 'hold AF' enabled
or shutter priority set , as to your observations Focus or shutter are not black and white they are fuzzy logic preferences focus priority will not guarantee in focus before shutter fires but favor it.

---------- Post added 07-04-14 at 12:51 PM ----------

QuoteOriginally posted by fgaudet Quote
And have customizable grouping options for the auto-focus points

---------- Post added 04-06-14 at 20:15 ----------



And have customizable grouping options for the auto-focus points
Could you explain what you mean?

the k3 allows
single point at any position in focus frame
9 point grouping anywhere within focus frame
25 point grouping anywhere within focus frame
27 point grouping

It difficult to see what other options would be sensible for a 27 point af frame, or indeed what advantage.

Last edited by awaldram; 04-07-2014 at 04:54 AM.
04-07-2014, 05:52 AM   #11
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QuoteOriginally posted by awaldram Quote
Sounds like you have 'hold AF' enabled or shutter priority set , as to your observations Focus or shutter are not black and white they are fuzzy logic preferences focus priority will not guarantee in focus before shutter fires but favor it.
I have tested with and without 'Hold AF' also I have Focus Priority set. It seems to be fuzzy logic in play and I will learn to live with it.
04-07-2014, 06:29 AM   #12
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QuoteOriginally posted by awaldram Quote
Could you explain what you mean?
Prioritizing focus groups, i.e. top right corner, top left corner, bottom right, bottom left, center... This would be great when tracking a single bird in a flock... prioritizing only one area would prevent the AF from jumping from one subject to another across the frame. The K-3 (any Pentax and most DSLR) considers every focus point as equal when tracking instead of prioritizing adjacent points. You cannot adjust tracking sensitivity or the tracking logic (fast moving/slow moving) useful when tracking a car driving by while you're panning or not or if the car is approaching facing you or driving by across the frame. You cannot adjust how quickly (or often) the camera will switch AF point instead of try to refocus the current one. This is useful when tracking erratic moving subjects (hockey, soccer, football). This is stuff you find on higher end Canon, granted they pack a lot more AF points but at 27, the K-3 is slowly getting there.

I only have a K5 with 11 points but if I am panning, the camera works much better at tracking when set to 5 points, at 11 it will try to focus on other points too quickly, I can only imagine the K-3 with 27... prioritizing or sensitivity would allow for more flexibility depending on your shooting style and on what you are shooting.
04-07-2014, 06:49 AM   #13
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QuoteOriginally posted by fgaudet Quote
Prioritizing focus groups, i.e. top right corner, top left corner, bottom right, bottom left, center... This would be great when tracking a single bird in a flock... prioritizing only one area would prevent the AF from jumping from one subject to another across the frame. The K-3 (any Pentax and most DSLR) considers every focus point as equal when tracking instead of prioritizing adjacent points. You cannot adjust tracking sensitivity or the tracking logic (fast moving/slow moving) useful when tracking a car driving by while you're panning or not or if the car is approaching facing you or driving by across the frame. You cannot adjust how quickly (or often) the camera will switch AF point instead of try to refocus the current one. This is useful when tracking erratic moving subjects (hockey, soccer, football). This is stuff you find on higher end Canon, granted they pack a lot more AF points but at 27, the K-3 is slowly getting there.

I only have a K5 with 11 points but if I am panning, the camera works much better at tracking when set to 5 points, at 11 it will try to focus on other points too quickly, I can only imagine the K-3 with 27... prioritizing or sensitivity would allow for more flexibility depending on your shooting style and on what you are shooting.
With K-3 you can select to have 9 points to track with and these you can move where you want them i.e upper left corner, center or whatever.
04-07-2014, 08:48 AM   #14
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From the Pentax JP K-3 page:
Feature 2?K-3 | RICOH IMAGING

QuoteQuote:
Zone select
You can choose a set of nine points forming a square, which can be shifted as desired. The PENTAX Real-time Scene Analysis System detects a subject placed within this square, optimizes the focus, and tracks its movement — all automatically.

Select-area expansion*
Choose one of 27 AF points to focus on the subject, and the K-3 automatically tracks the subject and refocuses on it with the help of the neighboring points, even when it moves away from the initial point. You can select the desired expansion area from S (eight points), M (24 points) and L (26 points).
Plus there are 4 AF Hold settings:

QuoteQuote:
AF hold setting
Even when the subject moves away from the in-focus point or the K-3 loses the sight of the subject because of some obstacle, the K-3 retains the in-focus status. Depending on the photographic conditions or your preference, you can choose one of three holding durations.
Plus auto-tracking and many other AF customisation tweaks. There's a lot to explore and learn about the K-3's AF. Unfortunately there is no good guide to it all that I've come across.
04-07-2014, 01:49 PM   #15
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Thanks rawr!
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