Frank writes:
<<<Actually, the Sigma 180mm 2.8 macro is also effective 115mm at 1:1
<<<If I may believe the formula I found some time ago ;-).
Wow, more than I would anticipate!
Basically all modern macro lenses indeed do drop focal length when they go to
1:1 but the working distance still much better with the longer FL at lower mag.
The "effective focal length" calculations are very very approximate with a
complex lens,
but give some estimate of the degree of FL shortening. My CV 180/4 in OM
mount goes to 1:4 and does well on extension with good working distance as the
FL shortening is much more modest--typical for primes.
Canon 100 f/2.8L - drops to 75mm
Nikon 105 f/2.8 G VR - drops to 78.5mm (25% drop)
Sony 90 f/2.8 G - drops to 70mm (22% drop)
Leica R 100 f/2.8 APO - drops to 75mm with elpro 1:1 adapter (no drop at 1:2)
Voigtlander 125 f/2.5 APO - drops to 95mm (24% drop)
Voigtlander 110 f/2.5 APO - drops to 87.5 (20% drop)
One advantage of the FL drop is less light is lost as less extension required.
Also the cam is easier to handhold as movement less magnified. As Moose points
out a key thing however is axial stability to stack or get optimal plane of
focus and that is not fixed by image stabilization.
Mike
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|