DigitalCameraReview.com
Pentax DA* 55mm f/1.4 SDM Lens Review
by JerryJ -  2/26/2009

Mention the name "Pentax" around photographers and most of them will immediately think of fantastic prime lenses. Pentax has long been famous for making some of the best prime lenses money can buy, and doing so at a reasonable cost. It's no surprise then that one of this year's most anticipated new lenses is the Pentax DA* 55mm f/1.4 SDM.

Pentax DA* 55mm f/1.4 SDM

If there is a single camera and lens manufacturer with a history of building exceptional prime lenses that people can actually afford, it's Pentax. Their FA 50mm f/1.4 prime is widely considered one of the best 50mm primes on the planet and their "Limited" series of FA and DA primes are consistently found on lists of the best lenses for serious photographers. When Pentax announced the DA* 55mm f/1.4 SDM lens, I was eager to see if this lens would be a worthy replacement for the old FA 50mm.


ERGONOMICS
The Pentax DA* 55mm f/1.4 SDM prime is offered only in the Pentax KAF3 lens mount, a modernization of the long-lasting Pentax K mount.

Pentax DA* 55mm f/1.4 SDM

With a crop factor of 1.5x on Pentax's current DSLRs, the lens has a 35mm equivalent range of 82.5mm.

Pentax DA* 55mm f/1.4 SDM

What separates the KAF3 mount from earlier versions is the addition of a contact for new lenses with a built-in Supersonic Drive Motor (SDM), and the removal of the old screw-drive auto focus connection. What this means is that the DA* 55mm is only capable of working in auto focus mode with SDM-capable cameras (K10D, K100D Super, K20D, K200D, and K2000). Older Pentax digital cameras can only use this lens in manual focus mode.

Design and Build Quality
The Pentax 55mm is a fast-aperture prime, designed to cover the moderate telephoto focal length range and deliver sharp, professional-level image quality in any type of lighting environment. On their official website, Pentax describes this lens as being ideal for "portrait, still life, low light photography, [and] weddings."

This isn't a $100 "kit lens" we're talking about. The DA* 55mm is a weather-resistant and dust-resistant lens with rugged build quality that befits its premium price range ($799). Fit and finish are first rate with the same quality construction seen on the DA* 200mm and DA* 300mm lenses.

Pentax DA* 55mm f/1.4 SDM

The included, bayonet style lens hood helps shade the front lens element and prevent flare, but since front lens element is slightly recessed there isn't much difference when using or not using the hood.

Pentax DA* 55mm f/1.4 SDM

Markings (distance scale in both feet and meters) are clear and easy to read and include a basic depth of field scale.

One feature that's worth mentioning is that the DA* 55mm lens uses fully automatic diaphragm control: you can't manually select the aperture by turning the diaphragm collar on the lens because there is no diaphragm collar.

Pentax DA* 55mm f/1.4 SDM

Optical construction is all-glass with nine elements in eight groups, with Pentax's Super Protect (SP) lens coating which protects the exposed lens elements. The filter diameter for this lens is 58mm.

Handling
As noted, APS-C style sensors in Pentax cameras have a 1.5x crop factor, so this 55mm lens performs like an 82.5mm lens. The longer focal length range makes this prime absolutely perfect as a portrait lens for general use, and the nine-bladed aperture diaphragm helps deliver spectacular bokeh to isolate your subject from the background.

The 55mm focal length and f/1.4 aperture also makes this lens a great replacement for photographers who are trying to replicate the look of old 85mm portrait lenses from the 35mm film days.


PERFORMANCE

Auto Focus
The Pentax 55mm lens is driven by Pentax's in-lens focus system. In theory this means focus is a little faster than lenses with the old screw-drive style auto focus, but the DA* 55mm didn't prove to be significantly faster than the old FA 50mm f/1.4 lens. In fact, depending on the lighting environment and subject there were times that the FA 50mm focused faster than the newer 55mm lens. Still, the 55mm is quite fast ... consistently faster than the 18-55mm "kit lens" included with most Pentax DSLRs.

Unfortunately, auto focus accuracy was something of a mixed bag with the DA* 55mm lens. For the sake of accuracy we tested the lens on three different Pentax camera bodies: the K10D, K20D, and K2000. The 55mm lens focused perfectly with the K20D and K2000, but we discovered that the older K10D consistently suffered from slight back focus when using this lens. The same K10D body has no back focus problems with any other Pentax lens, including the SDM-equipped DA* 200mm lens, so we can only assume that the K10D may require a firmware adjustment in order to avoid back focus issues with this lens.

To illustrate this back focus issue we setup the K10D and K2000 on the same tripod with the 55mm lens. Both cameras used the center focus point and locked focus on the number "5" on the ruler. The K2000 produced a correctly focused image while the K10D was focused behind the actual focus point.

Pentax DA* 55mm f/1.4 SDM
K2000

Pentax DA* 55mm f/1.4 SDM
K10D

Manual Focus
Focusing manually with the Pentax DA* 55mm lens is much easier than with older Pentax lenses. As with all lenses in the DA family (with the exception of the new 18-55mm DA-L), there is no need to flip the MF/AF switch on the lens barrel or camera body because this lens features "quick-shift focus" (full-time auto focus override).

All you have to is point the camera at your subject and turn the MF ring until the subject snaps into focus. You never have to turn off auto focus again in order to adjust manual focus. The manual focusing provides just the right amount of resistance when turning.

Image Quality
Overall the DA* 55mm f/1.4 is yet another excellent Pentax prime in terms of image quality and takes contrast and sharpness to new extremes.

Pentax DA* 55mm f/1.4 SDM

This lens produces sharp images with good edge-to-edge definition, smooth bokeh, and accurate color.

Pentax DA* 55mm f/1.4 SDM

If this lens has a weak point optically it's chromatic aberration and color fringing at the widest aperture of f/1.4. In fact, although almost every prime lens with a f/1.4 aperture suffers from some color fringing wide open, we were sad to see that the new 55mm lens seems to exhibit worse purple fringing at the center of the frame than the old FA 50mm f/1.4 lens. When stopped down to f/2.8 or more, the color fringing vanishes.  Given the fact that experienced photographers can fix purple fringing during post processing, this probably isn't a major problem for most.

Pentax DA* 55mm f/1.4 SDM

Pentax DA* 55mm f/1.4 SDM
100% crop

Pentax DA* 55mm f/1.4 SDM

Pentax DA* 55mm f/1.4 SDM
100% crop

Despite the color fringing at the widest aperture and focus issue with the older K10D, the new 55mm continues the trend of high quality prime lenses from Pentax. The DA* 55mm f/1.4 renders colors that are hue accurate, bright, and nicely saturated. This glass should be more than capable of resolving any detail needed for high resolution digital image sensors for the foreseeable future.

Pentax DA* 55mm f/1.4 SDM

As expected, the DA* 55mm f/1.4 shows no noticeable barrel or pincushion distortion. Flare and internal reflections are very well controlled, and the included lens hood helps limit lens flare even when shooting toward the sun.

Pentax DA* 55mm f/1.4 SDM

Vignetting (dark corners) was negligible at all apertures with and without the hood. Some very minor vignetting is visible at f/1.4 and f/1.8, but this is visible only to the trained eye under studio lighting conditions.


CONCLUSIONS
As most of our regular readers know, I have a special place in my heart for prime lenses, and for Pentax. Modern zoom lenses provide the most flexibility when composing, but prime lenses offer better low light performance and the ability to isolate your subject with shallow depth of field. The 55mm focal length on Pentax DSLRs works well as a general portrait lens, and the SDM auto focus motor makes this lens much quieter than previous-generation prime lenses.

In short, the new 55mm is an amazing lens with fabulous edge-to-edge sharpness, great bokeh, and exceptional build quality common to the best Pentax prime lenses. However, auto focus inconsistencies and some strong purple fringing wide open at f/1.4 make this lens a questionable value at full MSRP ... at least as long as the old FA 50mm lens is still available.

Pros:

Cons: