One of the two subjects in the photo has a softening effect

[picturisq]

I don't know how this happens, when I shoot two or more people, one of them appears slightly out of focus (more of a softening effect) whereas the other person/people are tack sharp. I contacted a pro regarding this and he couldn't work out why and said I had done everything correctly.

The camera body (Canon EOS 5D Mark II) as well as the lens (Canon EF 70-200mm f2.8 L USM) I am using are new (a month old). So I don;t know if it is to do with the sensor of the camera body. The softening effect is not confined to a specific part of the photo, it is random. When I take a photo of 4 people, 3 of them appear tack sharp whereas 1 will be slightly out of focus. I have played around with depth of field by increasing it to f16 but I still get the same result.

Any suggestions will be greatly appreciated.

[OsmosisStudios]

Sample are gonna be necessary, and full-res is imperative.

[ErikUngerPhotography]

I'm gonna go out on a limb and say it is a depth of field problem. The lower your your aperture, the shallower the depth of field. This means the plain of focus is smaller.

When shooting groups (2 or more people) if they are not all in the same plane of focus, then they will not all be sharp. Only those in the plane of focus will appear sharp.

[zona5101]

following on Erik's thought... the depth of field at a 10 foot camera-to-subject distance 200mm focal length and f16 yields only .68 of a foot depth of field...slightly over 6 inches front to back.

[sk66]

Originally Posted by zona5101

following on Erik's thought... the depth of field at a 10 foot camera-to-subject distance 200mm focal length and f16 yields only .68 of a foot depth of field...slightly over 6 inches front to back.

Yeah, and a horizontal FOV under 2ft....I don't think that's it. If using 70mm @ f/8 from approx. 15ft, or similar combination (~4ft wide FOV) the dof would be ~4ft.

Could be you are focusing too far into the scene..The DOF will fall 1/3 in front of the point of focus and 2/3 behind. If you are focusing too far into the scene the person at the front could be OOF.

Could also be edge softness if one of the individuals is at the edge of the FOV...but if it is bad enough to be a problem above f/5 with that lens; I'd think it was a bad lens.

[ErikUngerPhotography]

Do you happen to zoom in to focus and then zoom out to the wanted focal length? This will also mess up the focus big time.