D50[?] 70-200 focus issues .

[Desmond]

I may be answering my own question here . When I first got my 70-200 F2.8 VR lens I ended up sending my D80 and the lens to the agents for callibration due to "back-focus" issues . This weekend I used the D50 and 70-200 in darkish conditions at quite a distance .....

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Notice how the subject is not in focus ? This was not a once off , every picture with people in it ended up with me having to auto-focus on an object about 5 metres in front of the subject to get things in focus , even at F6.3 .
Today I did some more tests ....
It didn't seem to like the bright white peg at F2.8 and the cable behind the peg is in focus .

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But close up with good light was ok

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and I had thought it was a distance issue because within about 20 metres it was ok but on this shot it focused on the pole behind the one I was aiming at .

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But then I chose a subject further away with good contrast and it focused ok

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So is this an expected outcome for the conditions I was shooting in - am I expecting too much from the lens - or should it be performing better ?

 

[keko]

I think you're seeing motion blur... the exif of #1 and #2 show 1/100 and 1/160 @ 200mm. Remember the 1/focal length rule for shutter speed. So, you should be shooting at 1/350 or faster on a crop body. #3 is shot at 1/640.
Were you focusing and reocmposing your shot? What AF mode where you in?

Try faster shutter speed, no focus and recompose and test again....

 

[Desmond]

I think you're seeing motion blur... the exif of #1 and #2 show 1/100 and 1/160 @ 200mm. Remember the 1/focal length rule for shutter speed. So, you should be shooting at 1/350 or faster on a crop body. #3 is shot at 1/640.
Were you focusing and reocmposing your shot? What AF mode where you in?

Try faster shutter speed, no focus and recompose and test again....

I ended up having to focus on the heads of people 3 rows before the platform single servo mode focus with the AE/Af button set to focus lock as well , and point it at the stage to get clear shots . I know there would be some motion blur involved at those speeds but I was eventually at 1/250th iso 1600 with the same results .
Look at #4 , the pole in the centre of the frame is out of focus while the one to the left of it is in focus - unless the focus point is quite badly out of the centre of the focus square to the left .
Even at higher speeds the people were out of focus and the boards behind them were sharp .
In #2 motion blur does not affect the fact that the cable behind the peg is sharper than the peg itself .

 

[keko]

What I'd do is shoot on a tripod, two different lenses at the same focal length and f-stop with the same body and see waht happens to focus.
This should tell you where the problem is. I think you could use the 70-300G and /or the 18-200 for that. However, you won't be able to compare at f 2.8...
Does this happen with you r D40 and D70s as well?

 

[Desmond]

What I'd do is shoot on a tripod, two different lenses at the same focal length and f-stop with the same body and see waht happens to focus.
This should tell you where the problem is. I think you could use the 70-300G and /or the 18-200 for that. However, you won't be able to compare at f 2.8...
Does this happen with you r D40 and D70s as well?

My next step will be to try it on the D70S . I noticed a trend yesterday , bright light , close subject and high contrast no problem - soon as the subject lost a bit of contrast it lost-the-plot . I used the lens with a 2X converter at the surfing beach in bright sunlight with no real problems on the D50 . This weekend I'll connect it to the D70S . Thanks for the input .

 

[Desmond]

Today I did some more tests at shutter speeds over 1000th sec .

The boat in the background is more in focus , though it is closer the the centre of the frame .

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This bird provided some good contrast to focus on but since it was moving it can't really be counted .

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In this shot the centre is not focused properly while the one on the right is .

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With good contrast the focus looked right .

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The close up tests I dreaded doing provided a surprising result in that the high contrast area foused in front of the centre point for a change . I'll have to do some tripod tests tomorrow .

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