20D C FN 4 and 16 - understanding exposure metering...

troutstreaming

Hi All,

I just want to check if I understand how the 20D meters in Av or Tv modes. When I half press the shutter button, the 20D measures the light (depending on the meter mode set) and then fires at that setting when the button is fully depressed (only in One Shot Mode and AI Mode?) If I want to premeter on a different source, then I should point the camera at that light source, press the star button with my thumb, then half press the shutter to focus. If I want the camera to resume normal metering then I need to wait for some number of seconds for the camera to reset itself or pick a new metering target and repress the * button.

Now to custom function 16 - safety shift. If the safety shift is on, when does the camera decide to recalculate the exposure? Will it recalucalate continually while the button is half-pressed if lighting changes, or only at the moment of full-shutter press? Will it overide an exposure lock (* thumb button depressed)? Will having custom function 16 on add any time between full-press and shutter actuation?

OR am I better off setting custom function 04 to either setting 2 or 3 where the camera is only going to meter on the full press and shooting in Servo mode using the * button to lock down focus? I am shooting fast moving sports and cannot afford to have any extra lag between when I full press and when the shutter actuates, so want to minimize the likelyhood of additional lag. Is there a negative to having both Custom Function 4 and 16 set to something other than 0? Is there any advantage to it? Why does 16 not come enabled out of the box? And finally which method do others out there use - using one shot mode, prefocusing and relying on the 'safety' function to get the exposure correct at actuation or using AI servo with Custom FN 4 set to 2 or 3 and locking the servo focus at a prefocus spot with the * button. FYI - I seldom premeter and lock AE as in that sort of situation I move to manual mode, so I do not care if I lose the AE prelock function, I just want to miss fewer shots to timing or exposure errors.

The reason for this query - I have had some interesting exposure misses while prefocusing on a target spot this summer and am trying to understand how to minimize them. I have been using 1 Shot Mode, prefocusing on a spot (half-pressing) and then full pressing as the athelete reaches that point (rather than trying to track a moving object with AI servo through a cluttered area or missing my framing of athelete and background by tracking and trying to actuate when everything is in place while panning.) I am guesssing that some of my exposure problems have been due to the exposure getting set at the time of the half-press (if I understand exposure setting correctly) and then the subject differing greatly from that exposure setting at full press, but want to double check that before setting custom functions that I barely understand...

Thanks in advance for your help!

Andy

PS I am also trying to avoid shooting manual, as I am running around following the action and the background and lighting are continually changing. Reframing with the zoom and getting the timing right is chore enough.

troutstreaming

20D C Fn 4 Info

troutstreaming wrote:

Hi All,

I just want to check if I understand how the 20D meters in Av or Tv modes. When I half press the shutter button, the 20D measures the light (depending on the meter mode set) and then fires at that setting when the button is fully depressed (only in One Shot Mode and AI Mode?) If I want to premeter on a different source, then I should point the camera at that light source, press the star button with my thumb, then half press the shutter to focus. If I want the camera to resume normal metering then I need to wait for some number of seconds for the camera to reset itself or pick a new metering target and repress the * button.

Now to custom function 16 - safety shift. If the safety shift is on, when does the camera decide to recalculate the exposure? Will it recalucalate continually while the button is half-pressed if lighting changes, or only at the moment of full-shutter press? Will it overide an exposure lock (* thumb button depressed)? Will having custom function 16 on add any time between full-press and shutter actuation?

OR am I better off setting custom function 04 to either setting 2 or 3 where the camera is only going to meter on the full press and shooting in Servo mode using the * button to lock down focus? I am shooting fast moving sports and cannot afford to have any extra lag between when I full press and when the shutter actuates, so want to minimize the likelyhood of additional lag. Is there a negative to having both Custom Function 4 and 16 set to something other than 0? Is there any advantage to it? Why does 16 not come enabled out of the box? And finally which method do others out there use - using one shot mode, prefocusing and relying on the 'safety' function to get the exposure correct at actuation or using AI servo with Custom FN 4 set to 2 or 3 and locking the servo focus at a prefocus spot with the * button. FYI - I seldom premeter and lock AE as in that sort of situation I move to manual mode, so I do not care if I lose the AE prelock function, I just want to miss fewer shots to timing or exposure errors.

The reason for this query - I have had some interesting exposure misses while prefocusing on a target spot this summer and am trying to understand how to minimize them. I have been using 1 Shot Mode, prefocusing on a spot (half-pressing) and then full pressing as the athelete reaches that point (rather than trying to track a moving object with AI servo through a cluttered area or missing my framing of athelete and background by tracking and trying to actuate when everything is in place while panning.) I am guesssing that some of my exposure problems have been due to the exposure getting set at the time of the half-press (if I understand exposure setting correctly) and then the subject differing greatly from that exposure setting at full press, but want to double check that before setting custom functions that I barely understand...

Thanks in advance for your help!

Andy

PS I am also trying to avoid shooting manual, as I am running around following the action and the background and lighting are continually changing. Reframing with the zoom and getting the timing right is chore enough.

Hi all,

Still looking for thoughts on C Fn 4 - 3 in AI Servo with respect to getting better exposures and quicker shutter actuation times in quick moving sports while prefocus shooting at a set point- Anyone know if C Fn 4 -3 results in any appreciable shutter lag compared ot a pre-metered button press?

I did find several useful resources and discussions that have helped me better understand C Fn 4:

http://doug.kerr.home.att.net/pumpkin/20D_CF04_chart.pdf

and

http://photography-on-the.net/forum/showthread.php?t=46965&page=1

for anyone else interested in this topic.

And now thank that C Fn 16 is for when exposure settings have changed - at the time of metering - such that the camera can't expose properly and still retain the selected shutter or aperature setting (no more Aperature to open or close at a given shutter speed for instance.)

Andy