Lens or body problem?

mercphoto

I originally bought my 300/2.8 to shoot football with my 20D. I found the shots soft, as if focus wasn't spot-on. But for motocross and karts its been exceptional. That sport I usually shoot at f/8-10. I recently did a bike race, shooting the 300, mostly wide-open. Once again, soft on focus.

This is not apples-to-apples comparison. I do notice the 20D has the worst time with AI-Servo when the subject is moving nearly straight at me, as is case with the bikes and football. That may be part of it. Or, the lens is a touch off and the wide aperture lets this show. Or, when wide-open on a 2.8 the depth of field is just plain tiny and its operator error.

How to tell what the issue is?

wxwax

Take a static shot of something with the aperature set at 2.8.

Mine's fine at 2.8, no softness. But even on the 1DmkII, the autofocus can miss shots. It's very common, in my experience. If the 20D's autofocus is slower, then that might well be the issue.

Bob Bell

mercphoto wrote:

I originally bought my 300/2.8 to shoot football with my 20D. I found the shots soft, as if focus wasn't spot-on. But for motocross and karts its been exceptional. That sport I usually shoot at f/8-10. I recently did a bike race, shooting the 300, mostly wide-open. Once again, soft on focus.

This is not apples-to-apples comparison. I do notice the 20D has the worst time with AI-Servo when the subject is moving nearly straight at me, as is case with the bikes and football. That may be part of it. Or, the lens is a touch off and the wide aperture lets this show. Or, when wide-open on a 2.8 the depth of field is just plain tiny and its operator error.

How to tell what the issue is?

The 20D has a known AF issue with fast moving items coming straight at the camera. I was having problems with motorcycle drags at the 60 foot timer and there are issues with birds.

1DmkII and N are 100x better at targets moving right at you.

mercphoto

Bob Bell wrote:

1DmkII and N are 100x better at targets moving right at you.

Sigh.... $$$$$
Thanks for the insight just the same.

cmason

Bob Bell wrote:

The 20D has a known AF issue with fast moving items coming straight at the camera. I was having problems with motorcycle drags at the 60 foot timer and there are issues with birds.

1DmkII and N are 100x better at targets moving right at you.

A known problem??? I am not sure it is a problem as much as a limitation of how the camera is designed. A 20D has a 9 point focusing system, whereas a 1DsMkII has 45. A 5D has that same 9pt focus btw. So if an object moves out of a focus sensor, it has a good chance it will be out of focus. I have also found, as have others, that AI focusing makes some poor choices. This doesnt mean there is a problem with the camera, it just doesnt know what you really wanted to focus on. Instead, it basically picks the object moving more. For a single bird flying across the view, this is perfect. For 10 motorcycles jockeying for position, this can lead to the camera focusing on the wrong rider.

I prefer single pt focus, and then I make sure the focus indicator is on my subject before taking the shot. Sure, some pics are out of focus if the subject moves too much, but at least I know why.

By the way, this problem existed before autofocus cameras too, you know.

Bob Bell

cmason wrote:

A known problem??? I am not sure it is a problem as much as a limitation of how the camera is designed. A 20D has a 9 point focusing system, whereas a 1DsMkII has 45. A 5D has that same 9pt focus btw. So if an object moves out of a focus sensor, it has a good chance it will be out of focus. I have also found, as have others, that AI focusing makes some poor choices. This doesnt mean there is a problem with the camera, it just doesnt know what you really wanted to focus on. Instead, it basically picks the object moving more. For a single bird flying across the view, this is perfect. For 10 motorcycles jockeying for position, this can lead to the camera focusing on the wrong rider.

I prefer single pt focus, and then I make sure the focus indicator is on my subject before taking the shot. Sure, some pics are out of focus if the subject moves too much, but at least I know why.

By the way, this problem existed before autofocus cameras too, you know.

Cmason, Thx for your explanation. A single object, whether its a bird, football player, motorcycle coming straight at you, the camera will not focus correctly the majority of the time, even a duck swiming towards you is an issue. I use center point AI Servo 99% of the time. These same shots are captured at a lot higher rate with a 1DmkII.

This does mean there is a problem with the camera because functionally it should be able to focus using center point and 2.8 lenses. Denile is a river just accept it and stop trying to explain around it to people that use their cameras a lot.

Bill, I feel your pain. All I hear is how great the N is over the 1DmkII and I really can't justify the price at this time since I am trying to pick up a 500/4 IS later this year. I just end up working around it by pushing the angles. I'm not sure if you have that luxury at a track when you need publishable action shots. All of the guys I ran into at the track were shooting with 1D bodies so I am not sure if the 30D addresses this or not. Here is a 20D+70-200/2.8 hand held shot to cheer you up http://members.cox.net/b-bell/SEP318.jpg

mercphoto

cmason wrote:

A known problem??? I am not sure it is a problem as much as a limitation of how the camera is designed.

Thanks for your explanation, and you are of course correct -- it is a limitation of the camera. However its a rather surprising limitation. I have (had to) become rather good at keeping the center point on the subject, so that's not the issue - the camera knows what I am trying to focus on. And even then the camera does not track subjects coming nearly at me all that well. Its made me do two things: shoot more profile, or shoot f/8 and higher. I'll get a 1-series but only if I can find a way to substantially boost sales.

wxwax

mercphoto wrote:

Thanks for your explanation, and you are of course correct -- it is a limitation of the camera. However its a rather surprising limitation.

I reckon it would be unreasonable to expect a $1000 camera to have identical features to a $4000 camera, no?

mercphoto

wxwax wrote:

I reckon it would be unreasonable to expect a $1000 camera to have identical features to a $4000 camera, no?

Can't ya tell I'm trying to save $$$ ?

mercphoto

wxwax wrote:

I reckon it would be unreasonable to expect a $1000 camera to have identical features to a $4000 camera, no?

Let me clarify about my "surprising limitiation" comment. Would you expect a 20D to be able to accurately focus-track a bicycle coming at you at roughly 15 mph, at a distance of about 70 yards, with a rider wearing a decorative jersey (read that as: this jersey has lots of sharp lines to acquire focus on) ?

wxwax

mercphoto wrote:

Let me clarify about my "surprising limitiation" comment. Would you expect a 20D to be able to accurately focus-track a bicycle coming at you at roughly 15 mph, at a distance of about 70 yards, with a rider wearing a decorative jersey (read that as: this jersey has lots of sharp lines to acquire focus on) ?

I dunno. What I do know is that it apparently can't, and you have to spend an additional $3000 to get a body that can. If this put Canon at a competitive disadvantage, I'm sure they'd change things. I guess it doesn't.

cmason

wxwax wrote:

I dunno. What I do know is that it apparently can't, and you have to spend an additional $3000 to get a body that can. If this put Canon at a competitive disadvantage, I'm sure they'd change things. I guess it doesn't.

So doing the math (a bit rusty, I admit), it looks like you have a subject that is changing its focal pt by 22ft every second (15mph), or 1/4in per millisecond. So lets say it takes (500 milliesecond) half a second between you locking focus and taking the picture. Your subject has moved 11 ft in that half second.

Lets say that you can do it even faster: running 5 fps in burst mode: each frame captures the subject at 200 millisecond intervals, which means they have moved 4.4 ft between shots. I don't know the focus speed here, but the chances are good that the subject has moved considerably between each shot even in burst mode.

Not sure what you were expecting your camera to be able to do? There is a lot of focal range between focus and taking the shot, when done head on.

Anybody have info on the focus speed of these cameras?

Bob Bell

cmason wrote:

So doing the math (a bit rusty, I admit), it looks like you have a subject that is changing its focal pt by 22ft every second (15mph), or 1/4in per millisecond. So lets say it takes (500 milliesecond) half a second between you locking focus and taking the picture. Your subject has moved 11 ft in that half second.

Lets say that you can do it even faster: running 5 fps in burst mode: each frame captures the subject at 200 millisecond intervals, which means they have moved 4.4 ft between shots. I don't know the focus speed here, but the chances are good that the subject has moved considerably between each shot even in burst mode.

Not sure what you were expecting your camera to be able to do? There is a lot of focal range between focus and taking the shot, when done head on. I

Anybody have info on the focus speed of these cameras?

Cmason, that is a very good point. But if you change your angle by 10 degrees or so, the camera can now track just fine. So instead of 22 feet a second it might only be 18 feet. (Im very rusty as well). Is that such a huge difference?

mercphoto

cmason wrote:

So doing the math (a bit rusty, I admit), it looks like you have a subject that is changing its focal pt by 22ft every second (15mph), or 1/4in per millisecond. So lets say it takes (500 milliesecond) half a second between you locking focus and taking the picture. Your subject has moved 11 ft in that half second.

Lets say that you can do it even faster: running 5 fps in burst mode: each frame captures the subject at 200 millisecond intervals, which means they have moved 4.4 ft between shots. I don't know the focus speed here, but the chances are good that the subject has moved considerably between each shot even in burst mode.

Not sure what you were expecting your camera to be able to do? There is a lot of focal range between focus and taking the shot, when done head on.

Ok, here is what is really odd. Shooting karts (faster moving objects) I seem to have little difficulty in focus tracking. Granted my aperture is smaller as well.

So I guess the AI-Servo mode on a 20D with a 2.8 lens is just not able to accurately focus-track a moving object coming at it. Even a relatively slow one.

cmason

Interesting article. Old but likely still accurate:


[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]Sequence Control in the EOS 1 AI Servo AF System [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] The EOS 1 AI Servo AF system performs best with subjects that pass at least the minimum requirements for light level, subject position, subject contrast, camera shake, and subject motion, as outlined above. However, the process of photographing a moving subject goes far beyond simple AF detection. Once the photographer presses the shutter release, a complex chain of events takes place. First, the lens is driven (if necessary) to the correct focusing position. Next, the camera’s reflex mirror begins to rise. Then, the lens diaphragm is actuated to a predetermined setting, the shutter opens and closes, and finally the system is reset for the next exposure. This process is called Sequence Control. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Sequence Control requires the full integration of all EOS 1 systems, including AF, AE, viewfinder and LCD panel display, film transport, lens drive, shutter/mirror charging, self-checking, and others. To a certain extent, all motor-driven 35mm SLR cameras share the same sequence control characteristics. However, the way in which the AI Servo AF function is overlaid on the mechanical functions of the camera is unique to the EOS 1. This uniqueness is most clearly seen in the responses of the camera to various shooting conditions. In the following description, we will outline the possibilities: [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] A. Single Frame Shooting [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Single frame shooting, or the first frame of a continuous sequence, is handled the same way no matter what the conditions are: i.e., regardless of whether the EOS 1 body is used alone or with a booster, whether the subject is readable or not, with any EF lens type, etc. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] In this case, focusing begins when Switch-1 (SW-1) is turned ON. This condition occurs most normally when the shutter release button is partially depressed. Focusing can also be activated by the EOS 1’s AE lock button when Custom Function 4 (CF4) is ON, by partially depressing the switch of Remote Switch 60T3, or by using the Wireless Controller LC-2 Set. For the purposes of discussion, we will simply refer to the focusing being either ON or OFF. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] The photograph is taken when Switch-2 (SW-2) is ON. This occurs when the shutter release button is fully depressed, or through use of the EOS 1 selftimer, the selftimer/intervalometer function of Command Back E1, or various remote control devices. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] At this instant, lens drive immediately stops, the mirror is released, the lens diaphragm is stopped down as required, and the exposure begins. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Because the photographer (rather than the autofocusing system) controls the timing of the shutter release, Canon calls this shooting method release priority. The release priority method enables the photographer to shoot when desired, but it does not guarantee sharp focus. In fact, the first frame of a continuous sequence shot in AI Servo AF is likely to be out of focus, especially with a subject moving either toward or away from the EOS 1. [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] B. Second and Consecutive Frames in Continuous Sequence [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] In continuous sequence AI Servo AF shooting, shutter release timing for the second and consecutive frames in the sequence is controlled by the EOS 1’s autofocusing system. Canon calls this focus priority. However, it is extremely important to note that focus priority shutter release timing does not guarantee sharp focus. It simply means that the EOS 1 camera, rather than the photographer, controls the shutter release timing for these exposures. Here’s how it works: [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 1. Readable Stationary Subject: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] In this case, the focus is set once and remains the same for all consecutive exposures. For this reason, high framing rates (frames per second shooting speeds) are usually achieved. Focus Prediction is not required, and is therefore not used. [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 2. Totally Unreadable Subject: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] A good example of this type of subject is clear sky or any blank, smooth surface. As long as this condition remains unchanged, the EOS 1 will continue shooting at the highest possible framing rate. If you try to autofocus this type of subject before shooting, the lens will go through one search cycle (current lens position to minimum focus, then back to infinity), then lock at infinity and display a rapidly blinking focusing indicator in the viewfinder display. You can shoot as many exposures as you wish under this condition. However, the viewfinder display is extinguished during the shooting sequence. [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 3. Low Contrast Subject: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Many different subjects present this condition, especially human subjects when the focusing frame is positioned on smooth skin or non-patterned clothing. If the contrast level remains too low to read, the camera reverts to condition 2 as outlined above. If, on the other hand, the contrast level becomes readable, then the EOS 1 selects the most appropriate response from the following options: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 4. Adequate Subject with Steady Movement: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] This is the ideal subject type for the Focus Prediction Function of the EOS 1’s AI Servo AF mode. When the subject speed reaches a certain level, the EOS 1 identifies it as a moving subject and begins to use its Focus Prediction capability. In this scenario, the 3 most recent AF measurements are fed through a proprietary algorithm (formula) to determine subject direction, speed, and acceleration or deceleration rate. This information, added to the AF time lag and the release time lag information, results in a calculated focusing position which is input from the camera body to the lens microprocessor through the contacts in the EOS electronic lens mount. Then, the lens is driven to the calculated focusing position and the exposure is made. The scene is re-evaluated before the next exposure, and if the subject movement continues consistently in the same direction, the lens will be driven to the newly calculated position and the next exposure will be made. This process is repeated as long as necessary, subject to available battery power and film capacity. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Sometimes, during the evaluation period between frames, the situation may change suddenly. This can happen if another subject moves in front of the original subject temporarily, or if the photographer is unable to keep the AF frame centered on the original subject. In such a case, the EOS 1 continues to shoot at the most recent “good” focusing position. However, if the situation remains uncorrected for more than 0.5 second, the camera focuses on the new subject if possible, or determines it to be unreadable and then continues to shoot at the same focusing distance. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] The EOS 1 viewfinder indicates that the subject has become unreadable by means of the flashing AF indicator below the picture area, as described in Condition 2. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] There may be times when the photographer simply wishes to suspend focusing but continue shooting at a fixed focusing position (sometimes called AF Lock). The EOS 1 allows for this by the use of Custom Function 4, which makes AF operation independent from shutter release. In the case described, the photographer keeps on shooting by maintaining finger pressure on the shutter release, but suspends focusing at will by releasing thumb pressure from the AE lock button. [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 5. Adequate Subject with Excessive Speed: [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] There are actually two conditions of this type. The first condition occurs with a subject moving toward the camera, so close or so fast that the required focusing movement cannot be executed within a preset time limit. For USM lenses, the time limit has been set at 200 milliseconds (1/5 second). For non-USM lenses, the time limit is 250 milliseconds (1/4 second). If the subject requires more focusing time than the preset limit, the exposure is taken anyway at a focusing position that is as accurate as possible. However, this type of exposure will be out of focus towards the infinity direction. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] The second condition occurs with subjects that are simply moving too fast for the AF system to track. In this case, the subject is for all intents and purposes unreadable, so the camera reverts to Condition 2. This situation can occur when the camera position remains stationary and the subject is moving at a high rate of speed, such as a race car or a downhill skier. [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Condition 6. Adequate Subject with Irregular Movement:[/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]This is the most difficult type of subject for the AI Servo AF system to deal with. A very good example is the stop-and-start, forward-and-backward movement typically seen with a runway-type fashion model. As long as the model is walking towards or away from the camera, everything is fine. But if the model starts moving irregularly, as in certain dance steps, focusing accuracy may suffer. [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] If the subject simply changes direction, so that predictable movement in one direction is simply shifted into predictable movement in another direction, the Focus Prediction Function can usually adjust to the change with little or no loss of accuracy. However, if the subject movement becomes so irregular that it is no longer predictable, then the [/SIZE][/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] EOS 1’s Focus Prediction Function is cancelled. If the subject movement remains unpredictable, then the lens is continually focused to the subject’s most recently detected position. In other words, the focusing position will change if the subject distance changes, but the AI Servo AF system will not execute a false prediction. [/SIZE][/FONT]

mercphoto

Good info, cmason. Chalk it up to operator error and trying to get too much out of the camera. What are the options to make a 20D work in this situation then? Would it be better to simply slam the shutter button, rather than go half-shutter for a second and then click? (thus taking the AI-Servo out of the question entirely)

Thanks.

wxwax

How about prefocusing?

mercphoto

wxwax wrote:

How about prefocusing?

Doesn't work if you are trying to react to what you are seeing (such as a steering correction, etc.)

cmason

mercphoto wrote:

Good info, cmason. Chalk it up to operator error and trying to get too much out of the camera. What are the options to make a 20D work in this situation then? Would it be better to simply slam the shutter button, rather than go half-shutter for a second and then click? (thus taking the AI-Servo out of the question entirely)

Thanks.

You know, I am not sure of the solution here (better at math and Google than this :). But given the above, here is what I would try:

Set in AV mode, and put shutter at f/8 or whatever apeture you lens is most clear.
Put camera AI Servo focus mode, and take bursts of shots. At least one should be in focus given the above.

I have had lots of luck with single shot focus mode myself, but of course no experience with subjects moving directly at me head on. I have had little luck with AI Servo period, and refuse to use it. However, my subjects are usually soccer players, and more often than not, AI Servo tends to focus on the wrong subject, since all of them are moving.