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Old Oct 2, 2007, 2:16 PM   #21
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So even though I think the 51 AF point on the D300 is great, I also believe the double cross center AF point on the A700 shows a lot of potential depending on what you're shooting
If it's as fast as the Maxxum/Dynax/Alpha 7 film camera, I can't see where most shooters would need more. We're becoming spoiled. :-)

Here's a quote from a 7 year old description. I don't think KM will mind me posting it, since it's no longer being made, and they're no longer in the camera business:

http://ca.konicaminolta.com/products...eatures.html#b

High Performance AF Control The Maxxum 7's advanced AF system has greater processing power and improved AF software which allows it to analyze metered data and compute the speed and direction of a moving subject. The World's Fastest AF Control* The autofocus control's twin high-speed 16 bit CPU have a computation speed that is approximately 5 times faster than that of previous models. In addition, the predictive focus control's accuracy has almost doubled when compared to prior models.
*As of August 25, 2000. When using a 50mm f/1.4 lens under Konica Minolta's standard test conditions. 4 frames per second Continuous Drive The high-speed built-in motor drive allows continuous shooting of moving objects at 4 frames per second in MF mode*.
*3.7 frames per second in continuous AF drive.
(Without the aid of an external booster).
Predictive Focus Control Multi-Dimentional Predictive Focus Control System is capable of tracking abrupt changes in speed and direction, such as U-turns, while maintaining accurate focus.
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Old Oct 2, 2007, 4:20 PM   #22
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Personally, I program the * button to stop AF. So I don't have to move my shutter finger at all to stop AI-Servo focus (similar to your pumping the shutter to get it to "Track" the subject.) I use AI-Servo almost all the time to quite good success on both stationary subjects and moving subjects. If I don't like what it chose for focus (because the part I want is smaller than the AF point or - as you rightly point out - it can bit a little off), I can release * or fix it manually (since my hand is already on the focus ring - proper long lens technique helps here.)

But to me this is the same thing as it being a little off in one-shot and having to correct. You are right, though, that a truly stationary subject will get a miss-focus because AI-Servo thinks it will move and anticipates it. It will be right, then wrong, then right, then wrong and it keeps trying to anticipate the movement. I've gotten good at pressing "*" when its right.

Now, the reality is that most of my subjects are not stationary. A good number of birds don't sit still (a good number do. Herons, egrets, raptors can - but also move their head a lot,...) so I believe having it in AI Servo helps me.

What bugs me about AI-Servo and hunting when the AF is off the subject is how it *does* work, but only part of the time. I've tracked short-eared owls in flight with a distracting background. My 20D would very consitently lock on the background when I slid off the bird. The 1Dmk II N is much better in this regard. I've had my subject fly behind branches and it didn't shift to the branches (it tracked the bird) just as it's supposed to. And I've had it screw up royally and lock on the branches. Now, I can normally see the bird still so tracking it isn't hard and it locks back on correctly when it comes out from behind the tree. But its the inconsistency that I don't get. It *does* work. Even a fair amount. But it still (too often) doesn't.

Eric
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Old Oct 4, 2007, 5:00 PM   #23
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eric s wrote:
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Personally, I program the * button to stop AF. So I don't have to move my shutter finger at all to stop AI-Servo focus (similar to your pumping the shutter to get it to "Track" the subject.)
True but doesn't that involve more dexterity since you're using two fingers in place of one? Beside if you use * button how do you control the exposure if you want to lock the reading (i.e. black/white bird or dark/bright background) with partial metering? IMO exposure lock is as critical as AF especially when the * button is programmed to quickly overide the normal exposure with center or spot

BTW I also program the other button to the left of the * (i.e. WB) to quickly overide the 45 AF points for single center AF point only. This way my index finger is always controlling the AF/shutter, while my thumb can move between the other two buttons for AF selection and exposure controls (or even pressing on both at once by straddling them with my thumb)! :-)




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But to me this is the same thing as it being a little off in one-shot and having to correct. You are right, though, that a truly stationary subject will get a miss-focus because AI-Servo thinks it will move and anticipates it. It will be right, then wrong, then right, then wrong and it keeps trying to anticipate the movement. I've gotten good at pressing "*" when its right.
Why do you think the camera movements only apply to stationary object?

See JimC "Predictive Focus Control Multi-Dimentional Predictive Focus Control System is capable of tracking abrupt changes in speed and direction, such as U-turns, while maintaining accurate focus."

-> Most modern SLRs can detect rate of change (i.e. acceleration) and not just speed which is constant. For subject with varying speeds this is great, but it can also work against you when camera shakes are involved: for example a bird flying across at constant speed but if the unintended camera displacement is ahead it can also fool the prediction algorithm into thinking the bird into flying faster placing the focusing plane to be forward of it actual location, or behind if the prediction program thinks it's slowing down because of the camera shaking the other way - IMO you can get AF predicting error either way (fixed or moving object) when a camera is not held fixed correct? Actually with moving subjects don't you have the tendency to move the camera more than if a subject is standing still?

Don't get me wrong, in many cases AI-servo work great. I tried and use both but have more success with single-shot AF when the targets are smaller. It's a lot easier to track visually this way (i.e. see through the lens). beside in single shot AF you also have a visual confirmation of AF-lock by the lighting up (or sound) of the AF point(s) aligning on your subject which you don't get in AI-servo...


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Old Oct 4, 2007, 7:38 PM   #24
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NHL wrote:
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eric s wrote:
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Personally, I program the * button to stop AF. So I don't have to move my shutter finger at all to stop AI-Servo focus (similar to your pumping the shutter to get it to "Track" the subject.)
True but doesn't that involve more dexterity since you're using two fingers in place of one? Beside if you use * button how do you control the exposure if you want to lock the reading (i.e. black/white bird or dark/bright background) with partial metering?
Fortunately Canon has corrected that little snafu. They now have a dedicated back focus button on the mkIII. Also, the ai-servo performs MUCH better on stationary subjects - it operates like ai-focus mode was always supposed to. So that was another little improvement.

Also of benefit is the focus assist points - no longer do you need to choose 1 or all - you can choose to activate just the points on either side of the focus point. The system gives preference to the main point but it will use the assist points if it can't detect with the main point. Wonderful for that instant where you let the point slip a bit - this way the camera doesn't slip to the background. Again another nice improvement.

So, it isn't always about the number but refinements in approach that provide benefit.

The only thing I don't like is you can't use the joystick to select all of the 19 points - point selection works on two circles so you need to use the wheel to change which circle (outer or inner) you're working with. Still, all in all, Canon listened to the pros and made some very good tweaks.
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Old Oct 4, 2007, 10:38 PM   #25
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JohnG wrote:
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Also, the ai-servo performs MUCH better on stationary subjects - it operates like ai-focus mode was always supposed to. So that was another little improvement.
John - If you hold the shutter release on the MrkIII half way down does the lens still jitter back and forth on a stationary object?

My MrkII dither the lens focusing ring back and forth even when mounted on a tripod...
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Old Oct 5, 2007, 7:27 AM   #26
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John - If you hold the shutter release on the MrkIII half way down does the lens still jitter back and forth on a stationary object?
No - or if it does it is MUCH less noticable than the way my 20d behaved. On my 20d it was always a toss up on whether or not I'd keep focus on a stationary subject. That became less of a problem when I started using the * button for focus - once I got good focus I could simply remove my thumb and not worry about the camera losing focus.

But according to the white paper on the mk III, ai-servo behaves like ai-focus is supposed to - (i.e. if the camera detects the subject is stationary focus will not keep trying to fine tune) - that has been my experience as well.
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Old Oct 5, 2007, 8:35 AM   #27
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JohnG wrote:
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That became less of a problem when I started using the * button for focus - once I got good focus I could simply remove my thumb and not worry about the camera losing focus.
Isn't this the same as using one-shot AF (AF lock and stop) but using the index finger only while freeing the * button for exposure lock or partial metering?

-> I guess it's a trade off since what you guys gain here is be able to fire the shutter at will even when the AF hasn't been acquired. One-shot AF wouldn't have let you take the shot until at least one of the AF point has locked




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No - or if it does it is MUCH less noticable than the way my 20d behaved.
If it does - Isn't that what Rob Galbraith observed?
http://www.robgalbraith.com/bins/mul...8740-9068-9093

-> Check the lens focusing ring jitters. Clearly one of the lens position is not correct - Agree? Specially when in AI-servo the shutter has priority over AF?
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Old Oct 5, 2007, 8:44 AM   #28
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NHL wrote:
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JohnG wrote:
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That became less of a problem when I started using the * button for focus - once I got good focus I could simply remove my thumb and not worry about the camera losing focus.
Isn't this the same as using one-shot AF (AF lock and stop) but using the index finger only while freeing the * button for exposure lock or partial metering?
Yes - FOR THAT SHOT. That's the beauty of having a separate focus button. I don't have to switch modes when I want to get the benefit of one-shot. Let's say you're shooting an owl perched and facing toward you. You're happily shooting in one-shot mode and the owl takes off flying in your direction. If your in one shot mode - too bad, your out of luck.

But, by using AI-Servo and the separate focus button - you can lock, remove your thumb and take shots of him on the branch. When he takes off you can immediately engage ai-servo by putting your thumb back on. Sure one shot could get the take off but you can't track him coming toward you and get another shot when the time is right.

For sports it's even more critical since the dof is much shallower (typically shooting at 2.8 with distances less than 40 yards). Take baseball - assume I'm shooting from third base with a runner on first. I pre-focus on 2nd base and remove my thumb. If there's a play at 2nd I'm ready for it and don't have to focus at the last second. But if the player rounds 2nd (no play) I can track him and fire of 4 or 5 shots of him coming right toward me. I then get to choose which shot offers the best expression and stride. No way single shot is going to provide that for me.
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Old Oct 5, 2007, 8:58 AM   #29
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JohnG wrote:
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But, by using AI-Servo and the separate focus button - you can lock, remove your thumb and take shots of him on the branch. When he takes off you can immediately engage ai-servo by putting your thumb back on. Sure one shot could get the take off but you can't track him coming toward you and get another shot when the time is right.
Exactly, but that's where we differ...

When he takes off, like you, I can also re-engage one-shot AF by 1/2 press the shutter release again but the difference is I "pump" the shutter release when the AF point is on the bird. This is not sport and the target is smaller and not keeping the smaller AF point in AI-servo on the (smaller) bird will kick the lens into focusing the background where it'll take for ever to get the lens to focus back on - That is provided you can still see the bird (as you said because of the razor thin DOF)

-> Almost all my BIF pictures are single-shot AF :-)
BTW in sport - you guys have the benefit of constant lighting (and players for one do not change jersey in the middle of a game) which nature photographer don't so the * button is quite critical...
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Old Oct 5, 2007, 9:27 AM   #30
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If it does - Isn't that what Rob Galbraith observed?
http://www.robgalbraith.com/bins/mul...8740-9068-9093

-> Check the lens focusing ring jitters. Clearly one of the lens position is not correct - Agree? Specially when in AI-servo the shutter has priority over AF?
I can't explain it -but I just don't see the same problems RG sees. Obviously he's more experienced than I am, but there are other MkIII users that, like me, aren't seeing the problems he sees.
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