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04-07-2013, 03:15 AM   #121
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Speed is an illusion. It's the relative changes of size and these are going to be greatest, and thereby more demanding, with direct movement towards or away from the camera.

04-07-2013, 06:35 AM   #122
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QuoteOriginally posted by bullitt_60 Quote
It depends on how fast the subject is moving and what your subject is. "Sideways tracking" is most important in my book.
I'm sorry but that's a wrong headed thought .... focus is dependent on subject distance from the focal plane. Laterally moving subjects don't change that distance. If you look at your photos, you can see that it isn't the camera tracking lateral movement - it is YOU. It's called panning.

I'm not saying that auto-focus doesn't need to be precise and fast. I am saying that in your photos the AF didn't have to work a lot once initial focus was achieved. But you on the other hand had to keep the subject steady within the frame - at least within the limits of your chosen shutter speed.
04-07-2013, 08:06 PM   #123
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QuoteOriginally posted by JimJohnson Quote
I'm sorry but that's a wrong headed thought .... focus is dependent on subject distance from the focal plane. Laterally moving subjects don't change that distance. If you look at your photos, you can see that it isn't the camera tracking lateral movement - it is YOU. It's called panning.

I'm not saying that auto-focus doesn't need to be precise and fast. I am saying that in your photos the AF didn't have to work a lot once initial focus was achieved. But you on the other hand had to keep the subject steady within the frame - at least within the limits of your chosen shutter speed.
With all due respect, this is not correct as the distance to the focal plane is changing and at a high rate of speed. In the case of the photos I posted, the subject was roughly 450 feet down track when I started focusing it and was roughly 75 feet away from me when the photo was taken. Using ye ol' pythagorean theorem, that is a distance of 456 feet from the camera to the subject, making the total closing distance 381 feet. A car moving at 130mph covers the 450 feet of track distance in 2.3 seconds. The 381 feet of closing distance over that 2.3 seconds is 165 fps or roughly a closing speed of 112 mph.

Edit - There is actually a rapid deceleration that takes place right as the object enters the focal plane, for example at 50 feet of track distance the closing speed slows to 40 mph. However, that is over 2 tenths of a second. If you graphed the speed it would look like how a child draws a bird.

Last edited by bullitt_60; 04-07-2013 at 08:33 PM.
04-08-2013, 03:07 AM   #124
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Situations like this are a big part of the reason I learned to MF. I don't think any camera's AF is perfect when it comes to fast moving things. I'd rather just MF my lens and hold it there, old style. That being said I've had very little by way of problems with normal shooting of faster objects with my K-x and it's AF and I've actually shot some stuff of my niece and her soccer team, a local boy's baseball team, et all. Not every shot is crystal clear but I don't really expect that. I think that's asking a lot of any camera when it comes to things moving fast. People shot sports with fast film for generations before I came along. They had the same issues, but more limits. I've got more iso capacity than any of them dreamed of and nearly unlimited storage space. Given that I've usually got time to dicker with my settings, and I don't have to worry about running out of film doing it. The K-x actually does a pretty good job I think besides in AF when I choose to use it. I'm not complaining, shrug.

04-08-2013, 06:51 AM   #125
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Either way, Bullet, those shot are awesome! Focusing like that in the dark? Great stuff...
04-08-2013, 04:01 PM   #126
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An interesting thread that's prompted me to share some pics.

Using my K20 with a DA 55mm-300mm, these were taken almost head on using AF, and as you can see, especially with the Lamborghini, they were coming at me at some speed! Now I know that if I spent an awful lot more money I would get probably better results, but these aren't too bad!





04-08-2013, 04:12 PM   #127
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Decidedly impressive shots. However, I notice that all 3 had almost the same focus point. Where you using the AF to track these vehicles to this point, or had you pre-focused on this spot in the road and waited until the vehicle reached that spot?
04-08-2013, 04:23 PM   #128
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I used AF and followed them until they were in the air...

04-08-2013, 04:56 PM   #129
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I recently purchased a Nikon D7100. I still own and use a K-5. I prefer the K-5 for most things, but the autofocus systems are night and day. The Nikon acquires and holds autofocus tenaciously in continuous mode with 51 autofocus points whereas the Pentax is at best hit or miss under the same circumstances. In the most recent interview with Pentax Japan executives, posted on this forum, they said one of their priorities was to be a "world leader" in autofocus. That is a great goal and one they're far from now.
04-08-2013, 08:29 PM   #130
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QuoteOriginally posted by oeriies Quote
I recently purchased a Nikon D7100. I still own and use a K-5. I prefer the K-5 for most things, but the autofocus systems are night and day. The Nikon acquires and holds autofocus tenaciously in continuous mode with 51 autofocus points whereas the Pentax is at best hit or miss under the same circumstances. In the most recent interview with Pentax Japan executives, posted on this forum, they said one of their priorities was to be a "world leader" in autofocus. That is a great goal and one they're far from now.
Did you hear that many people here are reporting better autofocusing with the K-5ii? You are comparing the wrong two cameras.
04-10-2013, 08:51 AM   #131
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QuoteOriginally posted by IchabodCrane Quote
Did you hear that many people here are reporting better autofocusing with the K-5ii? You are comparing the wrong two cameras.
The right two cameras to compare are the ones you have access to. Even if it's not the latest and greatest someone has it can still be interesting to hear first hand impressions.


I'd like to see head to head AF comparisons:

1) Get a nice long rail (like you often see movie cameras on) and mount camera A on one end and camera B on the other end, pointed at each other and each on their own little 'car'
2) Set both to burst mode (both need to use the same fps) and AF.S, tape the shutter button down and send them flying towards one another
3) Salvage SD cards from the wreckage after the cameras collide
4) Most in focus shots wins
5) Losing cameras wreckage gets danced upon by fanboi holding the winning cameras wreckage

There's probably a less destructive way to do this, but this will double in settling the 'camera A has a more solid build than camera B' claim and we all love to multi-task.
04-10-2013, 10:30 AM   #132
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I was throwing a small stone for the dog to fetch and trying to shoot at the exact moment that the dog reached it and stopped abruptly. The dog was running in a direction directly away from me running at full speed and then doing a skid turn to pick it up.
I was using a K-r with a Tamron 18-250 zoom at F7 and 250mm. The K-r is not the fastest focusing Pentax and neither is the Tamron a particularly quick focusing lens (it is screw drive) but nevertheless it managed well enough. I used continuous AF with the centre point.

The cars are shot with the K-30 and the 18-135WR lens. I used the 'expanded area' continuous AF, locking onto the car in the windshield area just as it was coming out of the corner and shooting in continuous mode from that point onwards until the car was past me and receding, while also continuously adjusting the zoom throughout its entire range. About 7 out of 10 photos were perfectly focused. Unfortunately the lens wasn't wide enough to fit the car in the frame when it was side on.
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04-10-2013, 11:20 AM   #133
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QuoteOriginally posted by BrianR Quote
The right two cameras to compare are the ones you have access to. Even if it's not the latest and greatest someone has it can still be interesting to hear first hand impressions.
....
Sure, you can gather some impressions but the post I was responding to was one where more than an impression was made... it seemed to be a conclusion. You can't make a conclusion about Pentax AF performance when what you have in your hand is a camera that's no longer made.
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