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Sigma AF 18-50mm f/2.8 EX DC macro - Review / Lab Test Report |
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Lens Reviews -
Nikon / Nikkor (APS-C)
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Page 1 of 2
Review by Klaus Schroiff, published February 2007
Lens kindly provided for testing purposes by Michael Kaufmann!
Introduction
The Sigma AF 18-50mm f/2.8 EX DC macro is one of the more interesting third-party standard
zooms thanks to a comparatively large max. aperture. It is already the 2nd incarnation
of its kind by Sigma. Besides a change in the optical design the new variant offers a shorter
min. focus distance of just 20cm resulting in a max. magnification of 1:3 @ 50mm -
therefore the new "macro" addition in the lens' name. Nonetheless it is not a "true"
macro lens because the focus group does not feature a floating elements design
(typically found in dedicated macro fix-focal lenses) for improved close up performance.
At a price around 400US$/EUR the penalty on your bank account would remain quite manageable.
The Sigma is a DC ("Digital Camera") lens specifically designed for APS-C DSLRs where its
field-of-view is equivalent to ~27-75mm on classic full format cameras.
The lens is available in all major AF DSLR mounts (tested on the Nikon D200 here).
For whatever reason Sigma did not release any HSM standard zoom to date and the 18-50mm f/2.8 EX DC macro
follows this tradition - on Nikon it relies on a slotted AF drive screw operated by the camera.
Speed-wise there's no need for an ultrasonic drive whatsoever - due to a very short focus path
(~45 degrees) the AF performance is very fast. On the downside this design results in rather
delicate manual focusing and AF accuracy could be better. Thanks to internal focusing (IF)
the front element does not rotate during focusing. Unfortunately the focus ring does rotate in AF mode
which isn't really something to be proud of these days.
Similar to other EX ("Excellence") lenses the build quality is very decent but a little
worse compared to the more pricey EX lenses or pro grade lenses from the genuine manufacturers.
The lens features the typical EX crinkle finish and broad rubberized control rings.
Both the focus and zoom rings operate very smooth. Sigma also implemented a zoom lock
in order to prevent zoom creeping during transportation.
| Specifications |
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| Equiv. focal length | 27-75 mm (full format equivalent) |
| Equiv. aperture | f/4.2 (full format equivalent, in terms of depth-of-field) |
| Optical construction | 15 elements in 13 groups inc. 2x aspherical, 1x SLD and 1x ELD elements |
| Number of aperture blades | 7 |
| min. focus distance | 0.20 m (max. magnification ratio 1:3) |
| Dimensions | 79 x 86 mm |
| Weight | 450 g |
| Filter size | 72 mm (non-rotating) |
| Hood | petal-shaped (snap-on type) |
| Other features | - |
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