70-300 VR Back Focusing??

[seknsak]

I enjoy shooting my daughter's sports but I notice that some of my shots are out of focus and was wondering whether this is:

1) a back focus issue with the lens. Can some one explain technically what back focus is?
2) the AF-S on my D50 was not fast enough
3) a result of shooting wide open and DoF issue

I have the D50 focus setting at center focus. Below are two examples of shots that I would have expected to be in focus.





Don't get me wrong, I love this lens and 90% of the captures are like the one below. Are my expectations too high?

 

[goofball404797]

Do you have this problem when shooting static subjects?

 

[KhanhNg]

The lens is probably not back-focusing; rather, it's focusing on the background. Sometimes when the contrast between object and background is low, the camera can get confused and the lens can focus on something that is not intended. Your lens is fine.

khanh

 

[seknsak]

Do you have this problem when shooting static subjects?

No - only in low light when the AF-S hunts a bit but this is a given.

 

[seknsak]

The lens is probably not back-focusing; rather, it's focusing on the
background. Sometimes when the contrast between object and background
is low, the camera can get confused and the lens can focus on
something that is not intended. Your lens is fine.

khanh

Thanks! Your point makes sense.

 

[mibadt]

Hi,

It might be caused by using a too slow shutter seeped. For sports I'd recommend 1/500 or faster. AS already has been mentioned, you may verify it by shooting static object.
--
Regards,

Michael Badt

Photos gallery: http://www.flickr.com/photos/mibadt/

Nikon D80
Nikkor 18-135mm f/3.5-5.6G ED-IF AF-S DX
Nikkor 70-300mm f/4.5-5.6G IF-ED AF-S VR
Nikkor 50mm f/1.8D
Sigma 30mm f/1.4 EX DC HSM
Sigma 10-20mm f/4-5.6 EX DC HSM
Nikon SB800 flash

 

[seknsak]

Hi,
It might be caused by using a too slow shutter seeped. For sports I'd
recommend 1/500 or faster. AS already has been mentioned, you may
verify it by shooting static object.

I agree but EXIF on the pics above a 1/500, 1/640 and 1/1000 respectively. I had lots of sun on this day.

 

[Snapshott]

As mentioned already I believe the problem is what the camera is focusing on. In the first picture it appears that the focus point was the right side of the goal. You may want to play with your AF setting between closesed object and dynamic where you can choose the focus point.
--
Snapshott