At 10:07 AM +0000 11/30/06, Peter Hancock wrote:
Henning wrote:
I believe I explained why there's no point and no
advantage to designing telephoto lenses for
smaller senor cameras.
No size advantage. No weight advantage. No cost
advantage. Just a smaller market.
The 'wasting half the light' argument doesn't
fly. All long lenses could cover larger areas,
but are baffled to avoid too much extraneous
light bouncing around. For the smaller sensor
sizes tighter baffels could be installed, but the
EF lenses are already well baffled, so that isn't
going to gain you much.
OK, I guess I simply don't understand the optics. Nevertheless, it's
clear that if you simply compare like for like in terms of equivalent
reach, the small format is lighter, smaller and cheaper:
Sigma 70-210 f2.8, full frame: 1345g; 86.6 x 184mm; filter 77mm; price
620 pounds
Sigma 50-150 f2.8, digital sensor: 770g; 76.3 x 135mm; filter 67mm;
price 450 pounds
I know which I'd rather carry. As I originally said, Pentax have also
announced two new upmarket long zooms for digital. It'll be interesting
to see whether Canon hold their line.
Peter
The difference in size and weight of those two lenses is completely
due to the longest focal lengths of 210mm vs. 150mm.
Look at it this way: a 210mm lens of f/2.8 aperture has to have at
least a 75mm diameter piece of glass in front (210mm/2.8=75mm). A
150mm lens of f/2.8 has to have at least a 54mm diameter piece of
glass.
If the lenses had essentially the same design, the front element
would have 1.4 times the diameter, 2x the area and 2.75 times the
weight, just from simple geometry.
A 150mm lens is less than 3/4 as long as a 210mm lens. Figure it out
- a much bigger piece(s) of glass significantly further out for the
70-210.
No wonder it's a lot bigger, heavier, more expensive etc. Has nothing
to do with coverage.
--
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:[EMAIL PROTECTED]
|[ ]| http://www.archiphoto.com
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