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08-14-2018, 10:25 AM   #1
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Which lens focuses faster for action? D-FA 24-70 or D-FA 28-105?

I will be shooting the upcoming annual Walk-a-Thon at my son's school this fall with my K-1 (not a K-1 II). Kids will be approaching/walking/running towards me. The day is usually sunny and bright but there is a section of the field where trees provide shade for the kids. I can choose between the D-FA 24-70 and the D-FA 28-105 lenses. Which lens would focus faster and lock on quicker in order to fire the shutter with less delay? I understand AF speed is a complicated puzzle when considering the amount of light, speed of internal motors, weight of lens elements, etc.

I did see a delay in the D-FA 24-70 focusing last year. Focus point would be the head or upper torso. The system response was so slow that the kids moved forward enough so that the head / upper torso was soft but the lower body and feet were sharper. Stationary portraits or group shots were spot-on sharp so no front/back focusing issues.


(Side note : I am considering sending in my K-1 for the upgrade but I'm also thinking if that $500-ish is better spent on something like the K-1 II successor, an Oly M-1 Mk II, etc)

Thanks!

08-14-2018, 10:36 AM   #2
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QuoteOriginally posted by 6BQ5 Quote
(Side note : I am considering sending in my K-1 for the upgrade but I'm also thinking if that $500-ish is better spent on something like the K-1 II successor, an Oly M-1 Mk II, etc)
u4/3 gets people into thinking af is better because DoF tolerate more af lag, but high shutter speed often require high iso which is not the strong point of u4/3. D500 would get the job done, and for keeping full frame image quality the AF upgrade for the K1 would be a Sony A9, D850, D5, 1Dx II. I would highly recommend the 1Dx II, this is a great camera for shooting moving subjects.

Last edited by biz-engineer; 08-14-2018 at 10:41 AM.
08-14-2018, 11:02 AM   #3
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QuoteOriginally posted by 6BQ5 Quote
I will be shooting the upcoming annual Walk-a-Thon at my son's school this fall with my K-1 (not a K-1 II). Kids will be approaching/walking/running towards me. The day is usually sunny and bright but there is a section of the field where trees provide shade for the kids. I can choose between the D-FA 24-70 and the D-FA 28-105 lenses. Which lens would focus faster and lock on quicker in order to fire the shutter with less delay? I understand AF speed is a complicated puzzle when considering the amount of light, speed of internal motors, weight of lens elements, etc.

I did see a delay in the D-FA 24-70 focusing last year. Focus point would be the head or upper torso. The system response was so slow that the kids moved forward enough so that the head / upper torso was soft but the lower body and feet were sharper. Stationary portraits or group shots were spot-on sharp so no front/back focusing issues.


(Side note : I am considering sending in my K-1 for the upgrade but I'm also thinking if that $500-ish is better spent on something like the K-1 II successor, an Oly M-1 Mk II, etc)

Thanks!

I have taken pictures of races with people running straight at me with the K1 and DFA 24-70 and had no issues with focus.


https://www.flickr.com/gp/pearsaab/0BS81N


---------- Post added 08-14-18 at 01:04 PM ----------

QuoteOriginally posted by biz-engineer Quote
u4/3 gets people into thinking af is better because DoF tolerate more af lag, but high shutter speed often require high iso which is not the strong point of u4/3. D500 would get the job done, and for keeping full frame image quality the AF upgrade for the K1 would be a Sony A9, D850, D5, 1Dx II. I would highly recommend the 1Dx II, this is a great camera for shooting moving subjects.
Sony A7 Riii also great
08-14-2018, 11:47 AM   #4
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Can you prefocus on a given location and/or increase your f stop to get better results?

08-14-2018, 12:17 PM   #5
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@pearsaab : I took a look at your photos and clicked on a few to get some info on them. Our shooting style is very different. It looks like you were zoomed in to the max of 70mm and you set the lens to f/7.1. I usually shoot somewhere in the 40mm to 50mm range, vertically, with the runner taking up ~70% of the frame. My runners are much closer to me. The lens is at f/6.3, just a little faster than f/7.1.

In my case the only thing that helps me a little bit is setting the focus back manually to the minimum distance between shots (if possible). When AF is activated the focusing mechanism moves toward infinity while the runner is moving toward minimum focus. Both meet in the middle and *click* goes the camera.


@UncleVanya : I don't think prefocusing and waiting for a runner to hit a spot would work in my case. The kids run around the field in a counter clockwise direction. I walk around it clockwise. That lets us see each other. The kids love this because when they see me coming toward them they are ready to jump, wave their arms in the air, smile, etc. In most cases I can't predict what they will do or in which direction they go. It's like photographing bees. Prediction is hard.

One exception for the prediction - girls are more likely to stop and pose with their friends or an adult/teacher/parent whereas boys are more likely to ham it up and do something heroic and action oriented. Girls are more likely to pile into one huge gaggle but boys will pick one to three friends for their group shot.
08-14-2018, 12:28 PM - 1 Like   #6
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You'd probably get better results standing back further and using a longer lens for more depth of field. Shooting at 50mm, as the kids get closer to the camera, the lens has to move a long way to keep the kids in focus. The distance of focus movement is probably the same for infinity to 10 feet as it is from 10 feet to minimum focusing distance. As the kids get close to the camera it's much harder for the lens to keep up.

For FF, the 28-105 might do it, but the 70-200 at a longer distance would be ideal. You may be suffering from some counter productive technique.

Last edited by normhead; 08-14-2018 at 01:02 PM.
08-14-2018, 12:32 PM   #7
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Do you use back button AF? If not could doing that and using quickshift help? Or just manual focus after you are close with the initial back button press?
08-14-2018, 02:07 PM   #8
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I saw a video of those camera guys comparing the K-1 + DFA 24-70mm with Canon and Nikon equivalents, shooting an oncoming dirt bike, and the Pentax outfit won! I cannot comment regarding these two lenses on the K-1. Maybe someone besides pearsaab, whose comments must be taken very seriously, has personal experience to offer.

08-14-2018, 02:22 PM   #9
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QuoteOriginally posted by mikesbike Quote
I saw a video of those camera guys comparing the K-1 + DFA 24-70mm with Canon and Nikon equivalents, shooting an oncoming dirt bike, and the Pentax outfit won! I cannot comment regarding these two lenses on the K-1. Maybe someone besides pearsaab, whose comments must be taken very seriously, has personal experience to offer.
You think that will convince anyone maybe they should stop complaining about Pentax AF and start working on their technique? Or to put it more bluntly, it wasn't Pentax AF that was the problem, it was the guy holding the camera.
08-14-2018, 05:17 PM - 1 Like   #10
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If you're shooting wide open and close the danger is your depth of field won't cover enough of the body, just stop down, Boris … and have you ever seen diagrams of a camera's AF module?

The camera doesn't focus on a spot, it focuses on a vertical or horizontal line.

That's your challenge as a photographer.

I like shooting sports because the uniforms often feature clearer lines than a face can. Especially in shade!
08-14-2018, 09:45 PM - 1 Like   #11
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Prefocusing doesnt consist of waiting for the runner to hit the spot. Prefocus is used in combination with burst mode. The burst starts before the runner is in focus zone and ends after the runner has crossed that zone. In that case K1 crop mode offers higher burst rate and deeper buffer as much as 50 frames containing at least 1 frame in perfect focus and 3 frames with acceptable focus.

Last edited by biz-engineer; 08-14-2018 at 09:54 PM.
08-14-2018, 10:08 PM   #12
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I took this wide open with the Tamron 70-200 f2.8 on the K-1, tracking the riders and firing off a frame whenever they lifted their head (no point taking pictures of uninteresting or awkward body positions).





Pre-focusing is a very good strategy when you're not panning, you've got the background the way you want it to be and you wait for a subject to briefly appear. A bit of guessing is involved. DA20-40 Limited in FF mode.


08-14-2018, 11:54 PM - 9 Likes   #13
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Example of how pre-focusing works:
08-15-2018, 03:03 AM   #14
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QuoteOriginally posted by biz-engineer Quote
Example of how pre-focusing works:
Absolutely ripping photo! Should be on a magazine cover or part of the Apple TV screensaver.
08-15-2018, 09:11 AM   #15
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QuoteOriginally posted by normhead Quote
You'd probably get better results standing back further and using a longer lens for more depth of field. Shooting at 50mm, as the kids get closer to the camera, the lens has to move a long way to keep the kids in focus. The distance of focus movement is probably the same for infinity to 10 feet as it is from 10 feet to minimum focusing distance. As the kids get close to the camera it's much harder for the lens to keep up.

For FF, the 28-105 might do it, but the 70-200 at a longer distance would be ideal. You may be suffering from some counter productive technique.
Hmmm! I never thought about it like this. The focus throw between 70ft and 80ft on a long lens is probably much less than 10ft and 20ft on a shorter lens. I'm going to experiment with this before the Walk-a-Thon.

QuoteOriginally posted by biz-engineer Quote
Prefocusing doesnt consist of waiting for the runner to hit the spot. Prefocus is used in combination with burst mode. The burst starts before the runner is in focus zone and ends after the runner has crossed that zone. In that case K1 crop mode offers higher burst rate and deeper buffer as much as 50 frames containing at least 1 frame in perfect focus and 3 frames with acceptable focus.
Hmmm again! I get it but I'm not sure this would work in my scenario. Knowing my luck the kids will be smiling and looking at me outside the focus zone and looking elsewhere or blinking in the zone. They aren't going to know where the zone is or even that it exists.

QuoteOriginally posted by biz-engineer Quote
Example of how pre-focusing works:
That is wickedly cool!
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