At 10:35 3/10/02, Joel Wilcox wrote:
Make sure you focus at the long end and then zoom out. It is not meant to
be constant going in the other direction, as I understand it.
Joel W.
It's been my experience limited by the two zooms I've owned (and only have
one of them now):
The most accurate method for checking focus shift on a zoom is critically
focusing at the longest focal length and then pulling back to the shortest
length. It is inherently easier to focus at long end with the reduced
depth of field.
In going the other direction, from shorter to longer lengths, any
evaluation is confounded with greater difficulty in focusing as accurately
at the short end. Minor errors due to this and the greater depth of field
will be magnified when the lens is zoomed to its longest length. The
greater the magnification range of the zoom, the greater the potential for
this confounding effect.
-- John
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