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11-02-2017, 12:10 PM   #1
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Two things I don't like about the K-1 C-AF performance

Lots of people say the C-AF performance in the K-1 is weak. I think I have two specific performance issues I can bring up from my own experience shooting this year's Walk-A-Thon at my kid's elementary school.

1) Lag - slow shutter activation. The K-1 with a D-FA 24-70mm can acquire focus and track subjects decently well. It's the speed of the shutter firing that makes images soft. The kids who ran toward me leaned forward. Their chests were ahead of their feet. In all the images I captured their feet were very sharp but their chests and their faces were soft. Yes, I used SEL9. Yes, I set the focus position point correctly. Yes, I used a very high shutter speed in TAv mode (1/2000). We have to remember that the camera stops focusing when the mirror goes up and the shutter starts to cycle. It's during that time the subject moves forward and is now slightly out of focus. Focus is perfect-perfect for still subjects and even when panning.

Wish : I wish the mirror could go up faster. I wish the shutter could cycle faster.

2) SEL9 seems to pick the furthest subject in its selection area. Given two people side by side with one person standing 3 feet back the K-1 seems to focus on the further back person. It's like the camera wants to focus closer to infinity instead of minimum. I thought Nikon had an option in their menus to let the photographer decide the priority. Where is this in Pextax? Am I missing something very fundamental somewhere?

Wish : Give priority to focusing to closer subjects instead of more distant subjects.

Now, with all that said, I was still able to produce lovely 4"x6" prints from every image captured. The softness we see when pixel peeping at 100% on the screen disappears at that size. Some were good enough for 6"x8". My stills are sharp enough for 9"x12" and beyond to poster sizes if not banners.

11-02-2017, 12:23 PM   #2
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QuoteOriginally posted by 6BQ5 Quote
Lots of people say the C-AF performance in the K-1 is weak. I think I have two specific performance issues I can bring up from my own experience shooting this year's Walk-A-Thon at my kid's elementary school.

1) Lag - slow shutter activation. The K-1 with a D-FA 24-70mm can acquire focus and track subjects decently well. It's the speed of the shutter firing that makes images soft. The kids who ran toward me leaned forward. Their chests were ahead of their feet. In all the images I captured their feet were very sharp but their chests and their faces were soft. Yes, I used SEL9. Yes, I set the focus position point correctly. Yes, I used a very high shutter speed in TAv mode (1/2000). We have to remember that the camera stops focusing when the mirror goes up and the shutter starts to cycle. It's during that time the subject moves forward and is now slightly out of focus. Focus is perfect-perfect for still subjects and even when panning.

Wish : I wish the mirror could go up faster. I wish the shutter could cycle faster.

2) SEL9 seems to pick the furthest subject in its selection area. Given two people side by side with one person standing 3 feet back the K-1 seems to focus on the further back person. It's like the camera wants to focus closer to infinity instead of minimum. I thought Nikon had an option in their menus to let the photographer decide the priority. Where is this in Pextax? Am I missing something very fundamental somewhere?

Wish : Give priority to focusing to closer subjects instead of more distant subjects.

Now, with all that said, I was still able to produce lovely 4"x6" prints from every image captured. The softness we see when pixel peeping at 100% on the screen disappears at that size. Some were good enough for 6"x8". My stills are sharp enough for 9"x12" and beyond to poster sizes if not banners.
Seems like you have a "problem" which is pretty much the same as my current Pentax cameras: K5 and K3.
I don't own a K-1 but I suppose Pentax (Ricoh) hasn't yet improved that much in the AF department, even with the K-1.
My thoughts ... and I also have the same wishes as yours for recent Pentax cameras.
Hopefully, this will get better with the release of future models. In the meantime ... we have to live with it (AF).
11-02-2017, 12:35 PM   #3
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I do better with AF.s. I use AF.c for birds in flight, when they are in the air against a sky so, no confusion with where my subject is, no confusion with multiple moving subjects.

Cameras that are really good at this kind of thing cost a lot more.

Last edited by normhead; 11-02-2017 at 12:42 PM.
11-02-2017, 12:42 PM - 1 Like   #4
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To reduce the “shutter lag” have you tried turning off the shake reduction? When I’m shooting fast shutter speeds I turn it off and the camera becomes more responsive.

11-02-2017, 12:45 PM   #5
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By comparison to the K3, the K1 AF sensing is weaker due to some adaption made for full frame, but tracking algorithm of K1 is smarter, but there is some additional lag that K3 did not have. K1 AF tracking is a bit better, but K3 was more zippy. Anyway, tracking with a short lens doesn't work well. Tracking with DFA70-200 works better thanks to more separation between sharp and out of focus areas, and tracking with DFA150450 works even better.
11-02-2017, 01:54 PM   #6
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This seems like an area where predictive focus would be helpful - camera "sees" moving subject, camera knows how long before shutter release, predicts where to adjust focus and does so. This is what I understand is how Nikon and Canon work better than Pentax in some conditions (like the coming right at you examples).

This takes good predictive computations and may be more than we can ask with the cost of this camera.
11-02-2017, 02:04 PM   #7
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QuoteOriginally posted by UncleVanya Quote
This seems like an area where predictive focus would be helpful - camera "sees" moving subject, camera knows how long before shutter release, predicts where to adjust focus and does so. This is what I understand is how Nikon and Canon work better than Pentax in some conditions (like the coming right at you examples).

This takes good predictive computations and may be more than we can ask with the cost of this camera.
I'm pretty sure similar cameras like the D7200 do it.
11-02-2017, 02:14 PM   #8
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QuoteOriginally posted by normhead Quote
I'm pretty sure similar cameras like the D7200 do it.
I agree - but I think that's trickle down tech - I think they developed it for the big guns first. That initial cost of developing and proving out the tech will not be cheap.

11-02-2017, 03:29 PM - 2 Likes   #9
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Concepts like depth-of-field and plane of focus are surprisingly absent from this discussion ...

QuoteOriginally posted by 6BQ5 Quote
I thought Nikon had an option in their menus to let the photographer decide the priority.
Nikon doesn't (that I am aware of). Perhaps you were thinking of this diagram that Nikon includes in many of it's camera manuals, like this from the D4 manual:

11-02-2017, 04:24 PM - 1 Like   #10
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QuoteOriginally posted by rawr Quote
Nikon doesn't (that I am aware of). Perhaps you were thinking of this diagram that Nikon includes in many of it's camera manuals, like this from the D4 manual:
Ohhhh...I do wish that Pentax would add something like this to their manuals.


Steve
11-02-2017, 06:14 PM - 1 Like   #11
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QuoteOriginally posted by stevebrot Quote
Ohhhh...I do wish that Pentax would add something like this to their manuals.
Even something like this brief explanation of AF usage scenarios from the D750 manual would be nice to see in the K-1 manual. Most of the AF behaviours are very similar to the AF options of most Pentaxes from K-3 onwards with SAFOX 11 or 12.

11-02-2017, 09:35 PM   #12
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I have the most success with AF-C, SEL-9 or SEL-25, and auto focus hold low. Keeping the subject on the center autofocus point while acquiring focus and keeping the subject within the 9 or 25 points while tracking is critical. If anything my K-1 has less shutter lag than my K-3 which is good since with the lower frame rate I can't use the press and pray method to get a good shot. I settled on these settings using football, softball, volleyball, basketball, soccer, kung fu, and gymnastics to hone my skills.
11-02-2017, 09:55 PM   #13
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QuoteOriginally posted by 6BQ5 Quote
Lots of people say the C-AF performance in the K-1 is weak. I think I have two specific performance issues I can bring up from my own experience shooting this year's Walk-A-Thon at my kid's elementary school.

1) Lag - slow shutter activation. The K-1 with a D-FA 24-70mm can acquire focus and track subjects decently well. It's the speed of the shutter firing that makes images soft. The kids who ran toward me leaned forward. Their chests were ahead of their feet. In all the images I captured their feet were very sharp but their chests and their faces were soft. Yes, I used SEL9. Yes, I set the focus position point correctly. Yes, I used a very high shutter speed in TAv mode (1/2000). We have to remember that the camera stops focusing when the mirror goes up and the shutter starts to cycle. It's during that time the subject moves forward and is now slightly out of focus. Focus is perfect-perfect for still subjects and even when panning.

Wish : I wish the mirror could go up faster. I wish the shutter could cycle faster.
Yup the K-1 has some Lag but you can change some settings and reduce this.
I started my chronicles with the focusing lag issue with this post: Forum Pos 74 in K1 Autofocust

I found settings that work pretty well and some other considerations to take and listed them in this post: Post 111 in K1 Autofocus

At best I could get about 40% accuracy with moving subjects and a tight DOF. The issue wasn't the Lag for me anymore, but the K1's autofocus algorithm. It uses a hunting style with catch-in-focus to fire it when you set it to Focus-Priority. This hunting style can cause some complications. I am sure that with a fast focusing motor in a good lens you might go much higher than my 40%.

QuoteOriginally posted by 6BQ5 Quote
2) SEL9 seems to pick the furthest subject in its selection area. Given two people side by side with one person standing 3 feet back the K-1 seems to focus on the further back person. It's like the camera wants to focus closer to infinity instead of minimum. I thought Nikon had an option in their menus to let the photographer decide the priority. Where is this in Pextax? Am I missing something very fundamental somewhere?

Wish : Give priority to focusing to closer subjects instead of more distant subjects.
The best suggestion I have for this is to use a single focus point. Make sure your camera is set to allow you to select which focus point to use and set it up that way. But if you are going this way, it is a good idea to map out your actual location of your focus spots. Just so that you know where they really are.

In the end here are things that will help with action shots in the Z-axis with the K-1:
1) Increase your DOF a bit more than what you would think. (Sucks, I know!) In my case I used a DOF calculator for a while just to get a feel for how large it really is, since you cannot properly evaluate it on the back screen.
2) Fine tune your lenses. I used the Dot-Tune method
3) Planning - take your time and decide where the shot is going to be and set up for this. (Pre-focus to that area) In sports, this is where knowing the game and where it is going to go, helps a lot!
4) Practice with your lens to find the range where your lens is the most dead on target. Some lenses have a small throw for a large focus range, this can cause some hunting before the lens lands on the spot, using the K-1 algorithm. Lenses have a sweet spot when it comes to this and it is important to know this for the K-1. The K-1 brings these flaws out in shining colors!

There is quite a bit of woo-woo out there, it is going to be up to you to dial in your style with the K-1 when it comes to Z-axis action. It isn't the best action camera available, not even close. Many professional photographers have commented on this when they reviewed the camera. In some cases they skim over this topic and in others they shine a beaming light on it, but it is a common issue listed in most reviews. But with practice: you could get your action accuracy up there; as long as you manage the DOF well, and plan your shots, you should be able to hit 20-40% consistently. If you know your subject well and know where they will be, as well as get that subject when they are at the slowest in their Z-axis travel, you might even get up to 60% accuracy.

Contrasting lines are important for the focus system in the K-1 so lower light situations will have an affect on the accuracy as well. In a forest situation my accuracy fell to 10% with a moving target on a path. My subject didn't have well defined lines in the dim light and it played havoc on the focus system.

If you are planning on doing a lot more Z-Axis action, consider a second camera. 2351HD expressed his experience in this post: Post 113 in K1 Autofocus
Quote: "You buy a system for what you need it for, so when its great for somebody else if may not be the case for you, but thats fine too." by 2351HD

At the moment I don't do too much Z-axis action. If I suspect there is going to be some, then I bring the Nikon D3000 along (its small) with the K-1 for all the scenic shots. If I do have a greater need for action; I might get a D500, since I have access to existing Nikon glass.

Good Luck!
11-02-2017, 10:24 PM   #14
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Without optical stabilization, when the subject is moving who knows where the subject was when the focus happened. I was shooting ice skating, when the skater come close to the lens, the motion relative to camera frame is huge, and the DoF become very thin , no camera can keep up. Anyway, predictive AF is a causal process, there must be existence of prio subject position for the camera to be able to predict something. I wonder what people think with regards to what AF servo should do. If Pentax AF isn't good enough in such situation I would suggest to use another camera to see if that's a user issue or a camera issue.
11-03-2017, 02:55 AM   #15
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Are you using live view? I have found the camera seems to slow down when using live view, almost as though it's using a slower shutter speed or there is some sort of delay. Could be my settings but when I am hand holding shots I switch LV off.
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