Metering question

[SensePhoto]

My sister was playing around with our dog in the backyard yesterday, i decided to try out the new lens (EF 70-200mm f/2.8L IS). It was snowing and they were running all over the place. I shot in Av mode kept aperture at f4 and switched to auto focus since i didnt have enough time to manualy focus them chasing each other. What i noticed is when the metering was set to evaluate mode and the camera was deciding on its own what focus points to use the pictures came out slightly out focus, but when i manually switched to only use the center focusing point they came out crisp. Could it be because it was snowing heavily? Do you guys generally pick the focus point manually or let the camera decide, when shooting in AF mode that is?

 

[tirediron]

I don't speak enough Canon to comment on how their focusing system, but generally I do prefer to select my focusing point rather than let the camera do, but even when I do "let" the camera choose the points, I make sure I know what it is focusing on.

 

[Overread]

The metering mode should not affect the AF as such - it controls the metering of the scene whilst the AF mode is its own control totally separate. In the softer shots make sure that its not a case that the AF has locked onto somewhere other than your ideal - or that your shutter speed isn't too slow. AF by nature tries to lock onto the closest change in contrast values that it can find. If you leave it open to choose which point to use it might catch a tail - ears - legs - nose etc.. instead of areas you want in focus like the eyes.

Setting to a single AF point allows you to control that element of the AF by at least designating where the shot should be sharp in the scene. Middle point is generally the best in the camera; however higher level models have better outer points and support AF points in some cases so check to see what kind and what positions your AF points are.

 

[SensePhoto]

The metering mode should not affect the AF as such - it controls the metering of the scene whilst the AF mode is its own control totally separate. In the softer shots make sure that its not a case that the AF has locked onto somewhere other than your ideal - or that your shutter speed isn't too slow. AF by nature tries to lock onto the closest change in contrast values that it can find. If you leave it open to choose which point to use it might catch a tail - ears - legs - nose etc.. instead of areas you want in focus like the eyes.

Setting to a single AF point allows you to control that element of the AF by at least designating where the shot should be sharp in the scene. Middle point is generally the best in the camera; however higher level models have better outer points and support AF points in some cases so check to see what kind and what positions your AF points are.

These are specs of AF sensor on my camera:

• 9 cross-type user-addressable AF points (f/2.8 at center)
• Center point additionally sensitive with lenses of F2.8 or faster
• AF working range: -0.5 - 18 EV (at 23°C, ISO 100)

Metering:

TTL full aperture metering with 63 zone Dual Layer (iFCL)
• Metering range: EV 1 - 20 EV

Yeah this one has 9 AF points like 5D Mark II and i set to one in the middle and the pictures came out good. For some reason i though those were also metering points, still have a lot to learn thats why i like this site lol

 

[Overread]

The f2.8 centre point might well be why your middle points came out better focused with the f2.8 lens when in a more difficult lighting situation for the camera. The outer points should be decent enough since they are at least cross points.

Metering wise I think that outside of spot metering the middle point is always the one that the meter bases its work from - which is why some have metering (half press of the shutter button) and auto focus shifted apart so that the AF engage is on the back button of the camera. You can lock the exposure with a half shutter press and then use the AF at a different target point to lock the focus and then shoot.

 

[SensePhoto]

The f2.8 centre point might well be why your middle points came out better focused with the f2.8 lens when in a more difficult lighting situation for the camera. The outer points should be decent enough since they are at least cross points.

Metering wise I think that outside of spot metering the middle point is always the one that the meter bases its work from - which is why some have metering (half press of the shutter button) and auto focus shifted apart so that the AF engage is on the back button of the camera. You can lock the exposure with a half shutter press and then use the AF at a different target point to lock the focus and then shoot.

Oh never thought about that, i'll definitely give that a try, it makes sense.