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p.5 #6 · 70-200 F4 IS bad batch | |
RobertLynn wrote:
I thought that lenses were expected to be a little sharper away from their MFD? The only way I could think of it would be a way that I saw the "lens body calibration" explained.
Imagine a "Unit" doesn't matter what, but we will say "canon units". Your camera ships and to be in spec is -1/+1 unit (or 0).
Lenses are calibrated to be at -1/+1 units (or 0). You may try one that is at 0, and your camera is a +/-1, making it seem "softer" at the MFD, but moving it a bit further back and the performance increases. You could try one, and it's at +1/-1 and your camera is the same, and it seems better than another you tested. Then finally, you check another and it's at -1 and your camera is at 0, and it seems better a little before MFD, but sucks at the long/short end of the focal length.
I totally stole the "unit" from another thread, but I imagine it would be applicable to this scenario.
I don't think so, in MFD some of these lenses not only were back/front focus, the subject usually had some sort of haze/halo around it, I think this is a lens diffraction that someone was referring to. I don't think calibration is going to help in this regard at all. 
mfurman wrote:
Today, I tested three 70-200 f/4.0 L IS lenses with the date codes:
UV03, UV12, UW04
and all of them exhibited the problem (UV03 was the sharpest at 135 mm but the least sharp at 200mm - all at MFD). I also tested 70-200 f/4.0 L (UW01) and it was less sharp at 135 mm but also the sharpness was reduced slightly less at 200 mm (but the issue was the same).
I would have probably chosen the lens with date code of UW04 but it already had dust (three specs) inside!
man that's a bummer.....I guess getting a new replacement probably not going to make much difference, either I'll get another one just like this, or the one that is not as soft at 200mm but inferior at 135 or 70mm. Given those options I would rather have a very sharp 70 to 135mm....
Edited on May 07, 2008 at 02:00 AM
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