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10-01-2007, 09:36 AM   #16
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QuoteOriginally posted by JasonS Quote
YEP! I shot the A feature (top 10 qualifiers in own race) of the premier class today. I found that the cars that placed well were also the ones I happened to have the best pics of from the qualifying days. As a photog, I wasn't really aware what the qualifying times were.
Just so happens that the good drivers are also smooth and hit the same lines consistently. Which also makes them easier to shoot!

The results:
RC Pro Series BuggyA - a photoset on Flickr
I can imagine it must be harder with RC cars since they move so fast and are smaller. Nice work.

10-02-2007, 05:57 AM   #17
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QuoteOriginally posted by Toshi Quote
I can imagine it must be harder with RC cars since they move so fast and are smaller. Nice work.
Thanks!
Well, you can get LOTS closer to the whole track without fear of major injury. Although I did get beaned a few times by wrecks that went off track. Luckily, they burn off a lot of energy flipping and tumbling. Would hate to get hit by one full on. 7 pounds at 50 mph would hurt.

This one did:

10-02-2007, 09:53 AM   #18
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QuoteOriginally posted by JasonS Quote
This one did:
Ouch!.....

That looks like a pretty wide angled shot with lots of depth of field
(I downloaded the full-sized and looked at the EXIF info - Focal length = 18mm, f/8, - and was the exposure time really -0.2 sec?)

I have often wondered about "Predictive AF" -
where the camera uses algorithms to predict where the moving subject might be.

Predictive AF is touted to be useful for tracking fast moving subjects,
and could even help minimize moving out of focus during the shutter lag/delay
(eg: at 60mph - a lag of 0.10 sec, means the object would have moved 8.8ft!)
But this works only for linear or "predictable" motion - it doesn't work well for sudden or more random motion - like animals or kids.
(I don't think either the K100D (Super) or K10D has predictive AF).

BUT the point is plenty of sport photographers were very adapt/competent at capturing fast action using manual focus in the days before AF (and even auto exposure) ........

So there's a lot to be said about using pre-focus and adquate depth of field for capturing action.

Pre-focus by either turning the AF off -
or using AF and hold focus on pre-selected points of focus in the scene -
and using one's instincts/muscle memory to trip the shutter at the right time -
ie: the photographer now becomes the "predictive" engine -
and the photographer often is the more reliable "intelligence" over almost any automation.....

Relying on automation blindly without "intelligence" (understanding the limitations) -
would probably result in "unintelligent" results ....
of course, understanding the automation and using it with intelligence -
can be a very powerful combination .
10-02-2007, 10:45 AM   #19
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I have been shooting icehockey several years with Pentax. First *ist D and Tamron SP 180mm and nowadays K10D and Sigma EX 70-200mm f:2.8.

Some occasions I feel myself a bit amused because according some fellow shooters opinions I am doing something almost impossible


Last edited by Harald; 10-02-2007 at 11:01 PM.
10-02-2007, 11:50 AM   #20
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QuoteOriginally posted by UnknownVT Quote
I don't think either the K100D (Super) or K10D has predictive AF.

According to the K100D manual page 125, it does have predictive AF in AF-S and AF-C if the camera determines the subject to be a moving object. So, it probably depends on the type and speed of movement as to whether it works or not. I can't say I've ever noticed it doing it's stuff
10-02-2007, 01:35 PM   #21
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QuoteOriginally posted by SteveB Quote
According to the K100D manual page 125, it does have predictive AF in AF-S and AF-C if the camera determines the subject to be a moving object. So, it probably depends on the type and speed of movement as to whether it works or not. I can't say I've ever noticed it doing it's stuff
I think we might be reading the same thing on page 125 of the manual
- but interpreting it differently.


The manual says "track" and does not say anything about "predictive".

I think tracking means tracking by using multiple focus senors -
whereas "Predictive" uses an algorithm to predict where the object is going to be -
two different things.

Here's a post on another Pentax Forum that discusses Predictive AutoFocus - the section quoted from the PZ-1P (35mm film SLR) manual has very different wording and specifically uses the term "Predictive".

I searched the pdf version of the K100D manual (Download Manual) and could not find any instances of "predictive" or "predict".

So I think the K100D using multiple focus sensors can track an object -
but it does not have predictive autofocus to work out/predict where the object may be next..... does that make sense?
10-02-2007, 04:42 PM   #22
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I use pre-focus on my motocross photos about 75% of the time as I try to get the rider in a certain position, the rest of the time I am tapping the shutter release to allow the camera to tweak the focus as a rider comes towards me. Results? One out of every 10-12 frames ends up being out of focus.

When I was shooting Niagara Falls this weekend, I did notice that when focusing on the moving waters of the rapids and such, there were several red lights blinking in the viewfinder at various points on the frame. I think this is the camera trying to "track" the moving object

Last edited by mudnmoto; 10-02-2007 at 04:49 PM.
10-02-2007, 05:27 PM   #23
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QuoteOriginally posted by mudnmoto Quote
I use pre-focus on my motocross photos about 75% of the time as I try to get the rider in a certain position, the rest of the time I am tapping the shutter release to allow the camera to tweak the focus as a rider comes towards me. Results? One out of every 10-12 frames ends up being out of focus.
I have no doubt that there are issues with the Pentax AF system when tracking extremely fast objects moving toward (or away) from the camera. The system seems pretty good at picking out the moving object, even when its not exactly center. It also seems to track focus pretty well while watching through the viewfinder. I noticed that in AF-C you could hear the focusing motor working hard until right when the shutter is released. My theory is that the slight delay that occurs between activating the shutter and the focus motor "stopping" its search is where the problem occurs. Those RC cars were going around 30-50mph at the end of the straight. The "sharp" DOF seemed to be around 1 ft. at the focal length and aperture I was at. Seemed like AF always missed it by around 1 ft or so. At 45mph how many milliseconds is 12 inches? I'd do the math, but my bet is its about exactly the "delay" in the shutter triggering. Maybe a firmware update that would allow a focus offset for this kind of shot?
Nevermind, its easier to just manual focus anyway. Although my miss rate was over 30% on some areas of the track - those were the same areas were the AF was useless.
If the Canon AF system could perform in the RC car environment without added release lag, I'd be really impressed........ IF it was at the Pentax price point.

If Pentax would only open-source its firmware so we could tweak it to our needs.

10-02-2007, 06:21 PM   #24
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QuoteOriginally posted by JasonS Quote
At 45mph how many milliseconds is 12 inches? I'd do the math, but my bet is its about exactly the "delay" in the shutter triggering. Maybe a firmware update that would allow a focus offset for this kind of shot?
45mph is 66ft/sec (mnemonic is 60mph = 88ft/sec) -
so 1ft is traveled in 1/66 sec = 0.015sec.

This almost exactly 10x faster than the shutter delay in either pre-focus (hold AF or manual) as reported by ImagingResource.com review of the Pentax K100D -

Pentax K100D Digital Camera Perform - Full Review - The Imaging Resource!

Shutter response (Lag Time):
Full Autofocus
0.182 second
Time from fully pressing shutter button to image capture
Prefocused
0.149 second
Time to capture, after half-pressing and holding shutter button.
Continuous AF
0.148 second
This mode usually shows no speed increase with our static subject; we have no way to measure performance with moving subjects
Manual focus
0.150 second
For most cameras, shutter lag is less in manual focus than autofocus, but usually not as fast as when the camera is "prefocused"


So even though you missed, I think your reaction/instinct/muscle-memory got it about 90% right
10-02-2007, 07:18 PM   #25
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QuoteOriginally posted by UnknownVT Quote
Ouch!.....

That looks like a pretty wide angled shot with lots of depth of field
(I downloaded the full-sized and looked at the EXIF info - Focal length = 18mm, f/8, - and was the exposure time really -0.2 sec?)

This one really didn't. It hit the black pipe and tumbled into me, and the big rubber tire caught my leg. If the small "bumper" catches you, that hurts.

That pic was right as the sun came over the hill to my back. My exif however shows shutter speed of 1/149 of a second.

I was doing these shots by holding my camera out over the track and guessing at the framing. Thats why its wide and set for good DOF, since I really couldn't be assured of focus. I just tried to hit the shutter at the when they reached the spot that I'd preset. If I could go back in time, I would have stayed in this spot longer. These shots didn't appear to work in the small lcd. I think I could have got some real keepers if I stuck there. I went back later in the day after reviewing them on a computer, but the sun was in the wrong place...... Next time!

Last edited by JasonS; 10-03-2007 at 03:35 PM.
10-18-2007, 03:45 PM   #26
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MudnMoto:

Really? I almost never prefocus anymore, unless it's a particularly difficult shot (down and away). I use continuous AF as well. Very few of my shots are out of focus. Of course, If I KNOW it's gonna' be a difficult shot, I adjust my technique/setttings accordingly. I don't see how you can expect to grab that block pass, or endo, or look back, if you only prefocus? Just wondering.
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