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Old Jan 16, 2007, 11:00 AM   #1
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In the never ending struggle to get better/sharper focus in challenging light for sports photography, I have been experimenting with the custom function 04 settings.

For background, I have a Canon 20D and use a 70-200mm f2.8 lens shooting high school sports.

I have found a link that gives a good explanation of the four different settings for custom function 4--http://doug.kerr.home.att.net/pumpkin/20D_CF04_chart.pdf--

Also several posters have suggested that improved focus response might be achieved by shooting in manual mode and setting a custom white balance using an 18% gray card. The rationale for doing this, I believe, is that the camera ( a Canon 20D) does not have to do exposure calculations and in effect is dedicated to performing auto focus and therefore should focus "faster".

My Question:
If I am shooting in manual mode for shutter speed and aperture AND have selected a Custom Function 04 setting # 03, in which focus is now controlled by the *button and exposure is supposedly set when the shutter is fired. However, since I have pre-determined the "proper" exposure (and a custom white balance) with my manual settings for shutter speed and aperture, the camera is not really setting the exposure when the shutter is released.

Is this a correct conclusion and can I expect faster/better auto focus by doing this?

An alternative procedure is to set the Custom function 04 to the #1 setting. In this mode, focus is again achieved by pressing the * button and exposure is locked with a half press of the shutter button (in AI Servo mode). Again since I am setting exposure manually and using custom white balance, there appears to be no difference in this situation than the one previously described.

I realize this is pretty confusing and hopefully someone will understand and shed some light on this subject for me.

Thanks in advance.

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Old Jan 16, 2007, 11:41 AM   #2
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Well, I've never heard the argument that saving metering time will improve focus issues.

First of all, I'm not sure how setting a wb makes any difference to focus - wb is determined, I believe, after the image is captured. So whether you set a custom wb, select a preset one or use auto - that should all happen after the image is captured not when the camera is focusing.

Now, on to CFn 4:

CFn 4 has 2 benefits -

1, it separates focus from metering

2. It allows you to stop ai servo from continuous focusing

If you'r setting exosure manually there should be no difference in how mode 1 and mode 2 work (although I have no idea about what processing logic the chip actually goes through but those are decision steps shouldn't have any bearing on focus speed or accuracy).

If you're not metering manually the difference is whether each shot in a burst will have it's own meter reading or whether all shots in a burst use the meter reading of the half-press.

I haven't seen anything in forums or write-ups that indicates that one mode or the other impacts focus speed. It's an interesting thought but I've never heard it from a reliable pro before. Where did you get that tidbit from?

So, where does CF-4 help someone who is metering manually? It helps when you want to stop the constant re-focus of AI-Servo. For instance, say you want to pre-focus on the rim of a basket and wait for the ball or player to get there - Cfn 4 allows you to set focus and wait (of course you need enough DOF in this instance to be sure the player is still in focus or is going to be in the same focus plane). Or you may want a photo of the player shooting a free throw. It's unlikely their face is going to move forward or back much so you might focus while they are eyeing up the shot and then release the * button - that way when you fire the shutter the camera doesn't have to re-focus and you don't have to worry about the face moving off the focus point and ai-servo switching to something behind the player. The other argument is that you can simply stop focusing if another object moves into the frame in front of the object you're tracking. This one I don't buy as much - if you're not using Cfn-4 you can simply release the shutter button and have the same affect - the lens still stays focused at the same distance.

So, there are certain situations where Cfn 4 will help. But in general if you have a player dribbling towards you without another player in the frame, Cfn-4 will not give you faster/more accurate focusing on that single player.

Low light sports work is TOUGH - it's also why the 1-series canon cameras use a separate chip whose sole job is focus control.

JohnG is offline   Reply With Quote
Old Jan 16, 2007, 1:12 PM   #3
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Thanks for your response.

In a thread I posted back on 4/17/06 about improving focus there were several responses including one by jlacasci on 4/18/06 that made mention of setting exposure manually and using custom white balance to obtain better shots...I may have misconstrued the reponse.
Below is the post from jlacasci I'm referring to.

On 4/18/06 jlacasci wrote:
Here's a couple more suggestions... I shoot sports/post shots on my site to sell. I use a Mark II N and a 20D.

For situations where the light doesn't change much (indoors). I use a 18% gray card and set a custom my white balance, select a shutter speed and f/stop and leave it. This allows the camera to just focus and not have to do any AE processing every time you press the shutter. This is more important on the 20D! (The Mark II N has multiple processors for AE/focusing and the 20D just can't compete with this camera IMHO).

I reprogram the '*' button to do focusing and the shutter to just fire the camera.

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Old Jan 17, 2007, 8:20 PM   #4
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even in auto mode theres no noticable lag in the cameras ability to set the exposure compared to the time it takes to auto focus. if you want to shave off time you should try tv with af on manual. prefocus your shots, set the shutter to a faster speed. unless you need the af for the speed it has over manual focus. if the subjects are more or less around the same focus area and you absolutly need the fastest shot to shot then manual is the way to go. Iftheres just no way to get around using the af then i wouldnt worry about the camera setting the exposure, it can do that in a milli second.
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