Tell me why... Focus Issue

[BuS_RiDeR]

I use auto focus almost exclusively. Mainly because I have bad eyes and I don't trust what I see as in focus through the viewfinder to be correct...

However, when I opened up this image in Gimp, I notice that the doll's face was in good focus, while my niece is a bit soft. Now I know for a fact that I focused in her eyes....

My method: Used single focus point (middle), focused on her eyes, holding the shutter button halfway I recomposed... And this was the result...

EXIF Data:
Camera: Canon
Model: Canon EOS 50D
ISO: 100
Exposure: 1/1000 sec
Aperture: 2.8
Focal Length: 50mm
Flash Used: No

Lems used: Canon EF 50mm 1.8

Can anyone explain why the doll's face appears more clear than my niece's? Did I make a mistake? How can I correct it?

 

[Kerbouchard]

Well, for one thing, the dolls face is plastic. It's features are a lot more defined than your niece's. For another, at 2.8, shooting a subject that is that close, it may be that the focus and recompose was enough to move the focus plane enough to be noticable. Assuming you were within about 5 ft of her, your DOF is only about 2 inches.

If you are tilting the camera when you do your 'recompose', the shift in the plane of focus may have been more than your DOF could allow.

 

[BuS_RiDeR]

Well, for one thing, the dolls face is plastic. It's features are a lot more defined than your niece's. For another, at 2.8, shooting a subject that is that close, it may be that the focus and recompose was enough to move the focus plane enough to be noticable. Assuming you were within about 5 ft of her, your DOF is only about 2 inches.

This makes sense... I was quite close to her...

If you are tilting the camera when you do your 'recompose', the shift in the plane of focus may have been more than your DOF could allow

I did not rotate or tilt the camera after re-composing... But this is a good point that I will try to remember.

So, if I used a lens with a longer focal length I might avoid this?

Thanks for the quick reply.

 

[Overread15 3]

With a 50D I would instead use the outer AF points to lock the focus and compose the shot using them; the outer points on midrange bodies like the 50D are generally pretty reliable (not sure which positions but I'm certain the 50D has cross type outer points as well as the cross type middle point).

That at least means you don't have to use focus and recompose, which often requires refocusing a little after the re-composition.

 

[BuS_RiDeR]

With a 50D I would instead use the outer AF points to lock the focus and compose the shot using them; the outer points on midrange bodies like the 50D are generally pretty reliable (not sure which positions but I'm certain the 50D has cross type outer points as well as the cross type middle point).

That at least means you don't have to use focus and recompose, which often requires refocusing a little after the re-composition.

Hmmm... I see what you're saying. Thanks, I think I'll try that.