inquiry.

[nism]

hi all,
still very new to dslr territory and i have this (hopefully) quick question:
i've noticed that in some of my shots, especially those of people that they aren't as clear as i hoped they would be.
1. here we have a shot at 25%, i've got the AF points, basic exif. things look a little dark, but details look fine
http://img182.imageshack.us/img182/3965/t1yi5.jpg
2. at 100%, again over an AF point
http://img182.imageshack.us/img182/3812/t2ad0.jpg
is that quality i should be expecting? or is that an issue with the AF missing? the lens not doing something? or the settings of ISO100 and shutter of 1/250 (he wasn't exactly charging at me. it was late afternoon). i think i should have bumped up the iso

thanks for your time,
blake

[JMWallace]

Ok...lets see.

First off, try using ONLY the center focus point. It is dramatically more accurate. It looks like the bottom AF point hit is collar and the far right one hit his shoulder. Those locations are probably about 2 inches off the cheek where the center point hit. At 70mm with the 40D you were really reaching about 112 mm. At an aperture of 3.2, you would have a pretty narrow margin of error. And if he was moving...even more of a chance of error.

Looks like it was overcast enough to have popped it up to ISO 200...maybe even 400 to get some really fast shutter speeds and help to stop motion.

Also, if you know you are going to be shooting movng targets, set your camera from "ONE SHOT" to "AI SERVO".

Also, looks like the 40D may have the same affliction at the 30D in Av mode. Set your exposure comp to be +1/3.

hope that helps.

[Honest Gaza]

In order to calculate the DOF in focus for the 70mm focal length....don't we also need an idea of how far away the subject was ?

I also thought that the DOF was calulated on the actual Focal Length of the lens which in this case was 70mm (not Focal Length x Crop Factor)......but I'm happy to be corrected.

[nism]

ah i see, i see. thanks for the reply jmw. i'll keep it in mind for next time.

[JTL]

In order to calculate the DOF in focus for the 70mm focal length....don't we also need an idea of how far away the subject was ?

I also thought that the DOF was calulated on the actual Focal Length of the lens which in this case was 70mm (not Focal Length x Crop Factor)......but I'm happy to be corrected.Nope. The crop factor DOES affect the apparent DOF. There is more apparent DOF for the same lens on a crop camera verses it used on a FF camera. But, you need to keep in mind that a focal length's apparent effect on DOF is actually an optical illusion...

[nism]

yea in following this up, i found this DOF calc to be very interesting to me. kinda taught me a few things too
http://www.dofmaster.com/dofjs.html