D50[?] 70-200 focus issues .

Joined
Sep 17, 2006
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Ashburton , New Zealand
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 .....

Drama003.jpg
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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 .

focus009.jpg
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But close up with good light was ok

focus011.jpg
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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 .

focus020.jpg
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But then I chose a subject further away with good contrast and it focused ok

focus029.jpg
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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 ?
 
Joined
Jul 20, 2007
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143
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Barcelona
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....
 
Joined
Sep 17, 2006
Messages
12,773
Location
Ashburton , New Zealand
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 .
 
Joined
Jul 20, 2007
Messages
143
Location
Barcelona
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?
 
Joined
Sep 17, 2006
Messages
12,773
Location
Ashburton , New Zealand
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 .
 
Joined
Sep 17, 2006
Messages
12,773
Location
Ashburton , New Zealand
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 .
f28test001.jpg
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This bird provided some good contrast to focus on but since it was moving it can't really be counted .
f28test008.jpg
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In this shot the centre is not focused properly while the one on the right is .
f28test016.jpg
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With good contrast the focus looked right .
f28test031.jpg
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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 .

f28test029.jpg
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