SLR Gear, an offshoot website of the Imaging Resource, one of the web's most-trusted resources for all things digital photography, has just posted an in-depth review of the Pentax 20-40 f2.8-4 Limited lens, which is the company's first Limited Series zoom optic.
So, does the 20-40 live up to the high expectations brought about by its Limited billing? Short answer: yes and no.
Optically, the lens is a bit of a mixed bag. In terms of sharpness, the lens is a bit soft in the 20mm focal lengths when shot wide open. To correct this, stop down two clicks to get good corner to corner performance. Moving into the 30-40 range, the lens sharpens up nicely, with decent wide open performance and even better sharpness closed down a stop. As for vignetting and distortion, both are very well controlled and should not present any real problems in real-life shooting. Chromatic aberration? It's present, but not overly obnoxious. The worst CA occurs on the wide end of the zoom range when shot wide open.
Mechanically, the lens is top-tier, being of all metal construction. All markings on the lens are engraved and then filled with paint. The zoom ring has a retro, knobbed look and both the zoom and focus rings move easily but without slop. The lens also features a 9-bladed, rounded diaphragm. As a final touch, the lens is fully weather-sealed, employing 8 gaskets in all to keep out junk. Don't forget to partner this lens with an equally protected camera, though!
As for focus, AF is by way of a built-in motor, unlike many other Limited Series lenses, which operate by the old-fashioned slotted screw drive. Result: focus is quieter and faster than the screw drive lenses but not anything to write home about in absolute terms. Unfortunately, the lens is not inner focusing and the MF ring spins when in AF mode. The 20-40 Limited also employs the Pentax exclusive Quick Shift Focus System for instant manual override.
Overall conclusion? Lukewarm.
In all, the 20-40 Limited isn't a bad lens, but there's a problem: the price, which runs around $1000. If this lens were $750, it would be a great buy but, at a grand, one has reasonable expectations of better wide-open optics and the zoom range itself is rather limited. For $200-300 more, you can get the 16-50 f2.8 DA*, which has wider zoom range, constant f2.8, weather sealing, and a sonic drive AF. If you can live with a constant f4 and no weather sealing, there's the 16-45 f4, which sells for around $600.
In all, the 20-40 f2.8-4 Limited is a good lens, but one with some good competition, too.
For more info:
The Full Test
Hit the 'subscribe' button for automatic email updates when I write something new!