David Taylor wrote:
On 02/11/2012 13:58, Bruce wrote:

I think the moral of the story is that you could make a more expensive
superzoom that had good optical performance; however, it would not
sell because most people would not recognise its optical superiority
and therefore could not justify the higher price.

.. and many buyers would simply not /need/ the better optical
performance for the (size of) images they were producing. Optical
performance is not only criterion in such lenses and purchasing
decisions - the convenience of avoiding lens changes either for bulk,
speed or environmental reasons also matters.

I have the Tamron/Sony 18-250mm zoom, which I originally got as a
useful Swiss Army Knife of a lens for general carry instead of one of
the usual kit lenses when buying my first DSLR. It was reviewed at the
time of its introduction as having unexpectedly good performance. I
think one reviewer suggested they'd found a way to suspend the laws of
physics in terms of its IQ improvements over the previous 18-200mm
model. So I guess it may class as one of the new optically improved
superzooms.

I was surprised to discover that once I'd learned the importance of
careful manual focusing for critically sharp results that it was hard
to tell the difference between the 18-250mm at f8 and a good prime at
f8 in an A3 print if the light had been good enough to provide enough
post processing latitude for a little extra cosmetic post processing
(such as a little extra sharpening) on the zoom. At F11 diffraction
obscures the difference between its IQ and a prime at any size of
print or pixel-peeping.

Aperture has such a large effect on image IQ, and in different ways on
different lenses, that I have no sympathy with general remarks about
comparative lens IQ rankings which don't specify aperture.

--
Chris Malcolm