Pentax SMC DA 18-250mm f/3.5-6.3 ED AL [IF] - Review / Lab Test Report
Lens Reviews - Pentax
Monday, 04 February 2008 05:09
Article Index
Introduction
Analysis

Lens kindly provided by Norbert Warncke!

It is an open secret that the Pentax SMC DA 18-250mm f/3.5-6.3 ED AL [IF] is not a native design by Pentax but licensed from Tamron. The move isn't even unprecedented - Sony did the same - and it is actually a good idea. The tests of the Tamron version in Nikon and Canon mount were promising enough for sure. It is unknown in how far Pentax has added his own spices to its sibling - it is probably based on Pentax SMC glass elements and it uses, naturally, a localized finish to match the Pentax way of life.
Typical for DA lenses it covers the APS-C image circle only. The field-of-view is equivalent to a whopping 28-388mm on full format cameras - that's a 14x zoom ratio and an industry record at the moment although it'ssurely only an intermediate step to an inevitable 18-300mm incarnation. Interestingly Pentax managed to keep the price tag fairly close to the "original" Tamron lens at around 450€/US$ vs 400&euro/US$. The Sony 18-250mm is far more expensive for instance.

In terms of build quality the 18-250mm is a fairly typical Pentax DA lens based on a combination of plastic and metal parts. The zoom and focus control rings are not the smoothest around but Ok regarding the target market. The lens uses a duo-cam mechanism (two inner lens tubes) which extends when zooming towards to long end of the zoom range. At 250mm the lens is about twice as long as fully retracted (@ 18mm). Surprisingly the duo-cams show only a marginal tendency of wobbling despite the extreme extension - the question may be whether or how much this will change over time. The tested sample did not suffer from zoom creeping but Pentax implemented a transport lock (18mm only) just in case.

The lens has no internal AF motor and relies on a slotted drive screw operated by the camera. This generates some noise during AF operations and the AF speed is comparatively slow although reasonably accurate on the K10D. The lens does not feature a Quick-Shift system like some of the other Pentax zoom lenses.

Specifications
Equiv. focal length27-375 mm (full format equivalent)
Equiv. aperturef/5.3-f/9.5 (full format equivalent, in terms of depth-of-field)
Optical construction16 elements in 13 groups inc. 1x ED and 2x aspherical elements
Number of aperture blades7
min. focus distance0.45 m (max. magnification ratio ~1:3.6)
Dimensions86 x 75 mm
Weight455 g
Filter size62 mm (non-rotating)
Hoodsupplied, petal-shaped, snap-on type
Other features-




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