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06-30-2018, 12:29 PM - 1 Like   #1
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The Truth - K-1 II AF-C Final Follow-up (Spot AF)

So I went back to the dog park one more time, It was very hot out but my dogs brother from the same litter came along so more to photograph. This time I left AF Hold to Medium and the AF was set to center spot, 1/4000th sec shutter speed and I remembered to turn SR off.

Sorry I didn't produce the photo streams this time however the format is the same as the first test seen here The Ugly Truth About Pentax AF-C (Cuteness included) - PentaxForums.com and here The Ugly(Cute) Truth about AF-C Follow-up with Auto-9-Point AF - PentaxForums.com

Just a refresher on the rating system

1) Perfect, spot on focus on the face (or sideways on the body)
2) The camera got some part of the dog in focus (This could be subjective as to whether the camera+lens didn't keep up or whether it just chose a different part of the fur ball to track)
3) The camera failed but that could be because the dog got too close, or I couldn't follow the dog and the dog left the AF area (this could be subjective)
4) Total fail, the camera clearly lost focus for no good reason

1st sequence APS-C mode 10 photos in 2-3 seconds, Started towards me but mostly side on
Ratings (4,1,4,2,1,1,1,4,4,4)
40% Perfect, 50% the camera did its job (Combined #1 and #2)
Remove the last 3 as I should have stopped shooting and we get 57.1% Perfect and 71.4% the camera did its job.

2nd sequence APS-C mode 15 photos in 2-3 seconds, the dog ran straight at me, as it got closer the camera couldn't keep up, I really should have stopped shooting
Ratings (1,1,4,1,2,1,1,1,4,4,4,4,4,4)
40% Perfect, 46.6% the camera did its job (Combined #1 and #2)
Again remove the end and we get much higher ratios of 66.7% Perfect and 77.8% the camera did its job. It seems the trend of the camera losing focus, jumping ahead and regaining focus is still occurring.

3rd sequence APS-C mode 21 photos in 3-4 seconds, again the dog running straight for me and of course like always getting too close LOL
Ratings (1,2,2,2,2,1,1,2,2,2,1,1,1,2,4,4,4,4,4,4,4)
Just 28.6% perfect, 66.7% the camera did its job (Combined #1 and #2)
Yet again remove the ending and you get 46.15% perfect and 100% the camera did its job. The camera was tracking, but just not keeping up, here is a case where setting the AF adjustment to front focus may have help... then again maybe not.

4th sequence APS-C mode 20 photos in 3-4 seconds, the usual, the dog runs straight for me then gets too close
Ratings (2,4,2,1,4,1,4,1,1,4,4,2,4,1,2,2,2,1,4,4)
30% perfect, 60% the camera did its job (Combined #1 and #2)
Maybe I should have awarded a few 3's here but it seems that the camera didn't have an ideal grasp on what it was tracking, this could easily be part user error.

5th sequence APS-C mode 20 photos in 3-4 seconds, the dog runs straight or me, gets too close an by then I'm sideways to the dog
Ratings (2,2,4,1,1,4,1,1,1,2,2,4,4,4,4,4,4,4,4,4)
25% perfect, 45% the camera did its job (Combined #1 and #2)
Of course I should have stopped shooting well before the end, so lets consider this more of a 45.5% Perfect and 81.2% the camera did its job.

6th sequence APS-C mode 28 photos in 5-6 seconds, the usual story, straight towards me and gets too close.
Ratings (1,4,1,1,1,1,1,2,4,1,1,4,4,1,2,1,1,4,4,4,4,4,4,4,4,4,4,1)
42.9% perfect, 50% the camera did its job (Combined #1 and #2)
Alright, it seems like user error in this case, toward the end its not that the dog bot bigger but I lost focus on him and the camera didn't reacquire until the very last frame... lets assume I stopped shooting when I noticed the loss and take out the end including the final frame. This gives us a new ratio of 64.7% Perfect and 76.5% the camera did its job.

7th sequence APS-C mode 15 photos in 2-3 seconds, starts with one dog running toward me with another dog joining the chase mid sequence. And of course both get to close.
Ratings (2,4,4,1,1,2,4,2,1,1,4,4,1,2,1)
40% perfect, 66.7% the camera did its job (Combined #1 and #2)
Not much to say here, just an average run.

In total there are 129 photos in 7 sequences, 34.9% perfect and 55% the camera did its job. However if we leave out those bad endings where I really should have stopped shooting we get 93 photos in 7 sequences, 47.3% perfect and 75.3% the camera did its job. I really can't say spot focus, Auto-9-Point or SEL33 (Expanded Area 33) did any better. I can say Spot leads to errors where you lose the dog from the center so SEL9 or higher would help and so long as Auto-9 grabs the correct subject it will perform just as well. So choose the ideal focus mode for the subject but don't expect much difference. I'd say expect 40-50% ideal (perfect) and 70-75% where there is no focus error its just the camera didn't always choose what the user wanted. That leaves an expectation of 25-30% failure (at least with this subject, camera, situation and lens) of course as always YMMV.

40-50% perfect in this situation, not bad for a camera that isn't supposed to be designed/used for action


Last edited by MightyMike; 06-30-2018 at 05:08 PM.
06-30-2018, 12:51 PM   #2
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First, why "AF Hold to Medium"?

Second, focus failures as the dog gets too close are caused by the lens which must move it's mechanism at ever greater speeds even if the dog is going a constant velocity.
06-30-2018, 01:52 PM   #3
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QuoteOriginally posted by photoptimist Quote
First, why "AF Hold to Medium"?

Second, focus failures as the dog gets too close are caused by the lens which must move it's mechanism at ever greater speeds even if the dog is going a constant velocity.
1) Because when I had it set to low it seemed more than willing to jump targets, however even on medium it will still jump targets pretty quickly

2) The lens isn't as smart as you're trying to give it credit for, it does not have a motor to drive itself, the camera drives the lenses internal mechanisms and quite fast indeed, just not fast enough when things get ridiculous (wouldn't matter if you were using a 1D whatever and the fastest focusing lens in the range, too close is too close)... If you didn't catch it this lens is a screw drive lens, not SDM/HSM/PLM/DC or whatever term you want.

Now I could have got 100% in focus right up to very close to me had I used my Venus 12mm F2.8 and set it to the hyper focal distance but thats not what is being tested nor is it ideal... so in the 100-300mm (150-450mm equiv) range (100mm as the dog gets close) I doubt any camera would be able to maintain focus. Hence the reason for suggesting I should have stopped shooting and that the percentages should be higher if we disregard such foolish shooting behavior.
06-30-2018, 02:58 PM   #4
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QuoteOriginally posted by MightyMike Quote
1) Because when I had it set to low it seemed more than willing to jump targets, however even on medium it will still jump targets pretty quickly

2) The lens isn't as smart as you're trying to give it credit for, it does not have a motor to drive itself, the camera drives the lenses internal mechanisms and quite fast indeed, just not fast enough when things get ridiculous (wouldn't matter if you were using a 1D whatever and the fastest focusing lens in the range, too close is too close)... If you didn't catch it this lens is a screw drive lens, not SDM/HSM/PLM/DC or whatever term you want.
It has nothing to do with lens smartness. And it has nothing to do with the focus is being driven by the lens motor inside the camera or one inside the lens. It is more a problem with the design of focusing systems and how far the lens must move to handle something like a 1 foot change in the subject's location.

I don't know about the SIgma lens but on the Pentax FA-100-300 f/4.7-5.8, the screw drive has to run 10X as fast when the subject is at 8 feet compared to 40 feet. Thus, an object coming at the lens might lose tracking because the motor (where ever it is) simply can't move fast enough. Different lenses require different motor spin rates at different distances but generally require much faster spin at close distances. That's why I said losing focus may be the fault of the lens.

06-30-2018, 03:57 PM   #5
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Spot AF for AF-C? I suppose that might work well for a train on a track coming straight on. Oh! Sorry! I took the thread title to be descriptive of what is being done. Silly me for not reading the detail of the original post.

This thread titled "The Truth - K-1 II AF-C Final Follow-up (Spot AF)" must be referring to the name of the dog! More appropriately, it might be:
Some Tests - K-1 II AF-C Final Follow-up (9-point Auto)



Steve
06-30-2018, 04:12 PM   #6
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QuoteOriginally posted by photoptimist Quote
It has nothing to do with lens smartness. And it has nothing to do with the focus is being driven by the lens motor inside the camera or one inside the lens. It is more a problem with the design of focusing systems and how far the lens must move to handle something like a 1 foot change in the subject's location.

I don't know about the SIgma lens but on the Pentax FA-100-300 f/4.7-5.8, the screw drive has to run 10X as fast when the subject is at 8 feet compared to 40 feet. Thus, an object coming at the lens might lose tracking because the motor (where ever it is) simply can't move fast enough. Different lenses require different motor spin rates at different distances but generally require much faster spin at close distances. That's why I said losing focus may be the fault of the lens.
Yes you worded it wrong in your original post. All lenses will have this problem, the reason is if you make the movement more linear it would take forever to reach infinity so a balance is struck that allows the lens to focus from near to infinity relatively quickly at the cost of not moving fast enough at close range. Given this is the case there really isn't fault, its simply a fact of life.

Just for facts sake, on the Sigma 100-300mm F4.0 EX DG the distance between 6 and 10ft on the distance scale is just over double the distance between 20 and 50ft

---------- Post added 06-30-18 at 07:17 PM ----------

QuoteOriginally posted by stevebrot Quote
Spot AF for AF-C? I suppose that might work well for a train on a track coming straight on. Oh! Sorry! I took the thread title to be descriptive of what is being done. Silly me for not reading the detail of the original post.

This thread titled "The Truth - K-1 II AF-C Final Follow-up (Spot AF)" must be referring to the name of the dog! More appropriately, it might be:
Some Tests - K-1 II AF-C Final Follow-up (9-point Auto)



Steve
Ok you're comment is confusing... This is the 3rd in the line of tests with different AF choices, SEL33 (Expanded Area 33), Auto9 and Spot... Yes Spot AF for AF-C not that hard to do, and you don't need a train. If you go back to the first thread on the topic you'll see a clear suggestion that skill plays a big role in results even when using AF-C, heck if you can't keep the center point on the dog while he is running straight at you then maybe you have bigger issues than the capability of Pentax AF-C.

BTW the dogs name is Bandit
06-30-2018, 05:03 PM   #7
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QuoteOriginally posted by MightyMike Quote
Ok you're comment is confusing...
The original post is confusing. Unless it has been edited, it says:

QuoteOriginally posted by MightyMike Quote
This time I left AF Hold to Medium and the AF was set to Auto-9-Point, 1/4000th sec shutter speed and I remembered to turn SR off.
Got it...The test is Spot AF.

Center point on dog butt...in focus!
Center point on dog ear...not
Center point on dangling tongue...in focus!
Center point on grass...gong!
Center point on dog eye? Dog eye? Get real! I can't track brown eye on brown dog at 10 meters? (GONG!)

Edit: I actually get it. Since the actual point is not important, what is being measured is the ability of the AF system (sensor/motor/coupling/lens) to accommodate unpredictable Z-axis shifts, sometimes as little as a few centimeters in a few milliseconds time. Intended point of focus is easy since it is always center of frame. Genius.

Steve

Last edited by stevebrot; 06-30-2018 at 05:19 PM. Reason: Sanity
06-30-2018, 05:14 PM   #8
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QuoteOriginally posted by stevebrot Quote
The original post is confusing. Unless it has been edited, it says:
Ah! I see the mistake thanks, its been edited now

QuoteOriginally posted by stevebrot Quote
Got it...The test is Spot AF.

Center point on dog butt...in focus!
Center point on dog ear...not
Center point on dangling tongue...in focus!
Center point on grass...gong!
Center point on dog eye? Dog eye? Get real! I can't track brown eye on brown dog at 10 meters? (GONG!)

Steve
So I know I haven't posted photos this time HOWEVER you've made some silly assumptions, first off the dog is white, secondly the center point is much larger than you might think and more often then not in these photos its as large as the dog is in front view when running towards me. So its not like it will commonly be just a mere part of the dog in focus but a fair portion of the dog.

This is how the focus point size and area coverage actually appear as told to me by a Pentax service tech (I drew this up based on what they explained to me)



06-30-2018, 05:53 PM   #9
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QuoteOriginally posted by MightyMike Quote
So I know I haven't posted photos this time HOWEVER you've made some silly assumptions
The only assumption I made was that the dogs' motion was typical for a dog park (directed at things other than the owner). Thanks for clearing up that Bandit and brother were coming straight on. We crossed paths in our posting and there is an edit on my previous comment. My understanding now is that what you have done is fairly elegant in that user skill (or lack of) is fully controlled for since all points on a fairly large target are game and most are equivalent in value. There was plenty of "silliness" at play, but in the interest of not being dead serious.

Truth be told, my bias is that actual field conditions using a user's usual subjects and kit are the most valid test of a feature. Your tests follow that pattern, though the "truth" aspect is that the results are what you get and for the rest of us, YMVV. Our dogs might be faster or our lenses slower or we might have a slight tremor for which SR might compensate, but which is driving the AF sensor crazy. That is why I brought up the railroad example. With all components fixed and predictable it would be possible to fully profile the system. That would be silly, but would satisfy the physicists. As it is, I don't own a dog, though I might be interested in using AF on a moving train, though in that case, I would...dang! I do think I might use AF-C Spot if it were a fast pan with a short burst.


Steve

(...actually have been thinking of setting up some train shots...)
06-30-2018, 06:07 PM   #10
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QuoteOriginally posted by stevebrot Quote
The only assumption I made was that the dogs' motion was typical for a dog park (directed at things other than the owner). Thanks for clearing up that Bandit and brother were coming straight on. We crossed paths in our posting and there is an edit on my previous comment. My understanding now is that what you have done is fairly elegant in that user skill (or lack of) is fully controlled for since all points on a fairly large target are game and most are equivalent in value. There was plenty of "silliness" at play, but in the interest of not being dead serious.
Its a forum, this and silliness are bound to happen

QuoteOriginally posted by stevebrot Quote
Truth be told, my bias is that actual field conditions using a user's usual subjects and kit are the most valid test of a feature. Your tests follow that pattern, though the "truth" aspect is that the results are what you get and for the rest of us, YMVV. Our dogs might be faster or our lenses slower or we might have a slight tremor for which SR might compensate, but which is driving the AF sensor crazy.
So true the AF sensor really needs its on SR system IMO, however I find it best to shoot action with SR off as SR on while even slightly panning at high shutter speeds has int he past lead to some destroyed results at 100% due to the SR actually doing more than it was supposed to in a very very short period of time.

Yes YMMV in all the reports, however for the sample size its probably safe to say people should be able to achieve similar results as in 40-50% perfect, maybe not all the time and maybe even better some of the time but average it out and I think that evaluation should be fair.

QuoteOriginally posted by stevebrot Quote
That is why I brought up the railroad example. With all components fixed and predictable it would be possible to fully profile the system. That would be silly, but would satisfy the physicists. As it is, I don't own a dog, though I might be interested in using AF on a moving train, though in that case, I would...dang! I do think I might use AF-C Spot if it were a fast pan with a short burst.


Steve

(...actually have been thinking of setting up some train shots...)
I've taking a few photos of trains, at a museum, and possibly a few from on trains too but its not something I'll claim to know a lot about.
06-30-2018, 08:15 PM   #11
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I use AF mode AF.C, "Hold AF Status" to "Off', "1st Frame Action in AF.C" to "Release-priority", and "AF Active Area" set to "Spot". My performance tracking as a user determines the outcome of whether I am successful or not. If I am tracking, my shutter speed, aperture (depth of field) and ISO are proper, my metering is set to "Spot" mode, and the light is sufficient for the shot, my AF is successful in getting the images I want. Location type of the subject is not an issue, the AF system focuses on what I am tracking, whether it is from the side, back, or front coming toward me or not. The K-1 II AF has shown excellent consistency for me. That is just my personal experience. I know different users may use different methods and that is user choice.

Last edited by C_Jones; 06-30-2018 at 09:06 PM.
06-30-2018, 09:11 PM   #12
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QuoteOriginally posted by C_Jones Quote
I use AF mode AF.C, "Hold AF Status" to "Off', "1st Frame Action in AF.C" to "Release-priority", and "AF Active Area" to "Spot". My performance tracking as a user determines the outcome of whether I am successful or not. If I am tracking, my shutter speed and aperture (depth of field) are proper, my metering is set to "Spot" mode, and the light is sufficient for the shot, my AF is successful in getting the images I want. Location of the subject is not an issue, the AF system focuses on what I am tracking, whether it is from the side, back, or front coming toward me or not. The K-1 II AF has shown excellent consistency for me. That is just my personal experience. I know different users may use different methods and that is a choice, that is just what has worked for me.
I switch around the AF Hold status and have never found one that works 100% ideally... before they implemented AF hold Status it was a pain when the AF would switch targets in a blink. I've never used release priority however I never have believed focus priority ever worked as advertised. using AF-Spot as I did in this report is only good so long as you can keep that spot on target, as soon as its off target especially with no AF hold it should stop tracking what you want it to track. As for aperture and therefore DOF he camera really should be able to handle 300mm F4.0 at reasonable distances even if that means the DOF is shallow, no point in stress testing the AF tracking if you're going to stop down so much it becomes very forgiving. (not saying I don't do this on occasion, I just don't see it as a tough challenge for the system). I personally never liked spot metering WRT action, far far too variable especially on subjects and scenes that aren't one brightness. I prefer center weighted for its consistency.

I appreciate you sharing your methods, enough people have suggested release priority and no focus hold that maybe the next time I go out for this sort of photography I'll change things up a bit.

Just in case I wasn't clear I am very happy with the results I'm getting but I always want better.
06-30-2018, 10:51 PM   #13
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QuoteOriginally posted by MightyMike Quote
I switch around the AF Hold status and have never found one that works 100% ideally... before they implemented AF hold Status it was a pain when the AF would switch targets in a blink. I've never used release priority however I never have believed focus priority ever worked as advertised. using AF-Spot as I did in this report is only good so long as you can keep that spot on target, as soon as its off target especially with no AF hold it should stop tracking what you want it to track. As for aperture and therefore DOF he camera really should be able to handle 300mm F4.0 at reasonable distances even if that means the DOF is shallow, no point in stress testing the AF tracking if you're going to stop down so much it becomes very forgiving. (not saying I don't do this on occasion, I just don't see it as a tough challenge for the system). I personally never liked spot metering WRT action, far far too variable especially on subjects and scenes that aren't one brightness. I prefer center weighted for its consistency.

I appreciate you sharing your methods, enough people have suggested release priority and no focus hold that maybe the next time I go out for this sort of photography I'll change things up a bit.

Just in case I wasn't clear I am very happy with the results I'm getting but I always want better.
I also have used different ways to actually find what suits me the best for different scenarios/testing. I suppose that is how users learn and develop methods/knowledge along the way.

Have a nice weekend.
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