Pentax 55mm f/1.4 SDM SMC DA*

SLRgear Review
March 2, 2009
by Andrew Alexander

Released near the end of 2008, the Pentax 55mm ƒ/1.4 SDM SMC DA* utilizes Pentax's ultrasonic autofocus SDM (''supersonic drive motor'') system. SMC stands for ''super multi-coating,'' a longstanding technology used by Pentax to reduce flare and ghosting as well as improve light transmission through the optical elements of the lens. The 55mm ƒ/1.4 DA* goes one step further by adding ''a newly developed Aero Bright Coating'' which ''enhances image-description performance by effectively reducing reflections over a wider wavelength range.''

The 55mm ƒ/1.4 operates with an effective field of view of 80mm on a Pentax digital SLR camera body. The lens ships with a substantial bowl-shaped lens hood, and is available now for around $700.

Sharpness
The 55mm ƒ/1.4 is one of the sharper Pentax lenses we've had the opportunity to test. One of the hallmarks of this lens is its wide ƒ/1.4 maximum aperture; happily, sharpness performance at this setting is very good, just about 2 blur units across the frame. Stopping down to ƒ/2 improves the central area of the frame (~1-1.5 blur units) while leaving the corners at around 2 blur units. By ƒ/2.8, the lens is sharp all over and stays this way until ƒ/16, where diffraction limiting starts to become noticeable. Even then, image sharpness is excellent, at 1.5 blur units across the frame. Fully stopped down at ƒ/22, sharpness still doesn't exceed 2 blur units.

In short, just excellent performance from this lens at all aperture settings. If Pentax had a full-frame dSLR for us to test on, it might be a different story, but on their reduced-frame bodies this lens delivers nothing but sharpness.

Chromatic Aberration
When you buy a fast prime lens, you probably buy it to shoot at those wide apertures. It makes sense then that Pentax has optimized the lens towards the wider end of the aperture spectrum, and its resistance to chromatic aberration is at its best at ƒ/1.4. It shows slightly more CA both generally and in the corners as the lens is stopped down, but it doesn't exceed 6/100ths of a percent of frame height, even at ƒ/22. You can see some very slight magenta CA in images taken, but usually only in high-contrast situations; you can examine our sample photos to see if the results are objectionable to you.

Shading (''Vignetting'')
Corner shading isn't really a factor for this lens. The only time it's ever an issue is when shooting the lens wide open at ƒ/1.4, where the corners are 1/3EV darker than the center. At any other aperture, light falloff disappears.

Distortion
The 55mm ƒ/1.4 shows very slight barrel distortion, at +0.25% in the corners. The distortion is linear and is easily corrected in post-processing software, if you need your straight lines to be absolutely straight.

Autofocus Operation
Pentax's SDM focus system is both fast and quiet; the lens takes about a second to do a full rack through its focus range, but is seemingly faster in point-to-point focusing (it's hard to quantify this one, so you'll just have to take that one with a grain of salt). The 55mm ƒ/1.4 uses Pentax's quick-shift system, allowing you to override autofocus results by just turning the focus ring at any time.

It's worth noting that older Pentax bodies (such as our test platform, the K10D) require a firmware upgrade to enable autofocus on SDM lenses. Our upgrade occurred easily and without incident.

Macro
The 55mm ƒ/1.4 isn't a macro lens, with a reproduction ratio of only 1:5.9 (0.17x). The minimum close-focusing distance is 45 cm (around 18 inches).

Build Quality and Handling
The Pentax 55mm ƒ/1.4 SDM SMC DA* is solidly constructed: there was no flexing or rattling to be found. As well the lens features a gasket to add weather and dust resistance. The lens sports a black finish with a very light semi-roughed texture. At 375 grams (just over 13 ounces) it has a nice weight to it, balancing well on our K10D.

The lens features 9 rounded diaphragm blades to produce a smooth circular aperture. There is a recessed, windowed distance scale, showing the focus distance in feet and meters. A depth-of-field scale is provided but only shows indicators for ƒ/8 and ƒ/22. There is no infrared index marker. The only control other than the focus ring is a switch on the side of the lens which allows you to disable autofocus operation on the lens.

The focus ring is made of a softer rubber texture, using a pattern of repeating ribs which provides excellent traction for focusing manually. The ring is 3/4'' wide and turns about 120 degrees through its focus range. The range is limited by hard stops on either end. The lens will not focus past infinity. As the lens focuses the front element does move, but it never protrudes past the front part of the shell. As well, the element does not rotate. The lens uses 58mm filters.

The lens uses the PH-RBH lens hood, a bayonet-mounted, circular lens hood which adds an extra 1 3/4 inches to the overall length of the lens (it's relatively long for this lens). The hood features a flocked interior finish and a removable section which provides quick and easy access to rotate a polarizing filter. The hood reverses and attaches to the lens for storage.

Alternatives

Pentax 50mm ƒ/1.4 SMC P-FA ~$200
If you don't need the SDM ultrasonic motor, you can save a fair amount of money going with Pentax's previous offering in this category. We haven't yet tested this lens.

Sigma 50mm ƒ/1.4 EX DG HSM ~$500
Sigma's 50mm ƒ/1.4 is available in the Pentax mount, and should autofocus properly on Pentax bodies which support SDM lenses. Unfortunately, we haven't yet tested this lens, either.

Conclusion
There isn't much to add that we haven't already covered: excellent results for sharpness, great resistance to CA, little to no corner shading or distortion. Quick and silent autofocus; rounded aperture blades; and to top it all off, a great lens hood that you probably won't even need given the lens' shrouded design. Pentax has produced a fantastic lens with the 55mm ƒ/1.4 DA*, however the only sticking point could be its high price point: at over $700, it's one of the most expensive 50mm-style lenses of any manufacturer. Based on our test results however, you definitely get your money's worth.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.