HD Pentax-DA 20-40mm F2.8-4 Limited

General Image Quality

The focal lengths offered by the 20-40mm lens range from wide-angle at 20mm to long normal at 40mm.  Since the zoom range also includes "normal" focal lengths like 30mm and 35mm (roughly 50mm-equivalent on film/full-frame), the lens is able to offer about the same degree of magnification as what the human eye sees.  This makes it a perfect everyday companion for your DSLR.

Zoom Range

The zoom range is a modest 2x, but still provides for some big variations in the rendering of a scene.

We illustrate the zoom range in two ways: First a scene taken from the same vantage point at 20mm and 40mm, next the same scene at 20mm and 40mm, but this time we moved the vantage point so as to keep the magnification of the truck the same.

Same Vantage Point
20mm	40mm
Same magnification of the truck
20mm	40mm

The 2x zoom range gives you plenty to work with, though the 20-40mm certainly isn't a telephoto lens at the long end, nor is it an all-in-one lens.  Still, it's great zoom range for serious photographers who like to shoot at "normal" focal lengths.

The presence of zoom does allow you to control perspective most easily than with a prime, as you can choose to zoom with your feet to avoid perspective distortion, or simply zoom with the lens when the former is impossible, inconvenient, or undesirable.

Color and Contrast

When pairing the 20-40mm with a Pentax K-3, we found it to produce warm, accurate color tones that were rarely in need of correction.  The contrast was very good except when wide-open; more details on this can be found on the Sharpness page. The HD coating does a great job of reducing aberrations, like on other HD lenses, so ghosting and flare was rarely an issue in practice.

Subjective Remarks

Overall, the 20-40mm Limited delivers very pleasing images and it is fun to use in the field. We found ourselves using focal lengths between 30 and 40mm more often than the wider settings due to the more "normal" field of view that they offer.  Even though vignetting can easily be observed in uncorrected indoor photos and landscapes, in-camera lens corrections do away with it fully in out-of-camera JPEGs.

Because the 20-40mm offers a maximum magnification of 1:5 at the long end, it doubles as a great close-up lens, arguably better than all other Limiteds save the dedicated 35mm Limited Macro.  The high magnification is complemented by beautiful bokeh, so we greatly enjoyed using it for hand-held flower photography.  The lens also works very well for landscapes at 20mm.

Refer to the next 5 pages for more specifics on the optical performance of this lens as well as a host of formal tests.