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Pentax SMC DA 40mm f/2.8 Limited Pancake Lens Review

Gary Wolstenholme reviews the Pentax SMC DA 40mm f/2.8 Limited pancake lens.

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Handling and features
Smc Pentax 40mm Limited
This compact 40mm pancake lens is part of the Pentax Limited range, which signifies that it is one of their top-end optics. It has a bright maximum aperture of f/2.8, costs around £380 and only protrudes from the lens mount by 15mm. On a Pentax DSLR this lens provides an angle of view equivalent to a 60mm lens used on a 35mm camera.

Pentax recently introduced another 40mm pancake lens with their K-01 camera, so it will be interesting to see whether this lens is still worth the extra cost.
Smc Pentax 40mm Limited

Pentax SMC DA 40mm F/2.8 Limited Pancake Lens Handling and features

The slender lens body of this 40mm pancake lens is constructed from high quality plastics and protrudes just 15mm from the camera when focused to infinity. The lens only weighs 90g, but even so this is nearly 40g more than the newer XS lens. The quality of materials and workmanship is excellent, with this lens feeling much more solid than the XS lens. When fitted to the Pentax K-5 body used for testing, this lens makes quite a compact system, at least for an SLR.

Focusing isn't performed internally, which is par for the course with pancake lenses, but the filter thread does not rotate, making it perfect for use with polarising and graduated filters. The 49mm filter thread size is standard for Pentax, so it shouldn't be too difficult to pick up accessories to fit. A thin manual focusing ring rotates during auto-focus, but it is adequately recessed to prevent it accidentally catching your fingers during operation. Manual focusing action is smooth, but not particularly well damped. A distance scale is provided, but no hyperfocal scale has been marked on the lens barrel, which is a shame. The Pentax 'Quick Shift' focusing system has been implemented on this lens, which means manual adjustments can be applied once the lens has focused automatically.

Although focusing is screw-driven, it locks onto subjects very quickly. The older screw-driven system does generate more noise than newer silent focusing lenses do though.

The minimum focus distance of 40cm is fairly typical for pancake lenses. A maximum magnification of 0.13x is possible, which may not be best suited for frame filling close ups images of small subjects.
Smc Pentax 40mm Limited


Pentax SMC DA 40mm F/2.8 Limited Pancake Lens Performance

At maximum aperture, sharpness in the centre of the frame is already excellent, although the clarity towards the edges of the frame lags behind somewhat. Stopping down the aperture improves sharpness across the frame, with the largest gains being seen towards the edges of the frame. Good sharpness across the frame is achieved at f/4 and excellent sharpness is realised at f/8.

Resolution at 40mm

How to read our charts

The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column.

The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple.

For this review, the lens was tested on a Pentax K-5 using Imatest.

Chromatic aberrations are well controlled, with fringing remaining around half a pixel width between f/2.8 and f/8. Stopping down further increases CA levels towards the edges of the frame, but as it only just exceeds 0.75 pixel widths, this level should pose few issues, even in large prints, or harsh crops from the edges of the frame.

Chromatic aberration at 40mm

How to read our charts

Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.

Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

For this review, the lens was tested on a Pentax K-5 using Imatest.

Falloff of illumination is reasonably controlled for a lens with an f/2.8 maximum aperture. At f/2.8 the corners of the frame are 1.11 stops darker than the image centre and visually uniform illumination is achieved with the lens stopped down to f/5.6 or beyond.

Only a very slight amount of barrel distortion is present in images taken with this lens. Imatest detected 0.586% barrel distortion, which will be very hard to spot, unless straight lines very near the edges of the frame run absolutely parallel with the frame border. The distortion pattern is uniform across the frame, so if you require absolutely straight lines, this low level of distortion should be relatively easy to correct.

During testing, this lens proved itself quite resistant to flare and contrast levels remain good, even when shooting into the light.

Pentax SMC P-DA 40mm f/2.8 Limited Sample Photos

Value for money

With this lens being one of the 'Limited' line from Pentax, it carries a slight price premium. This lens is available for around £380. The newer XS 40mm pancake lens is slightly cheaper at around £290, and although this lens is slimmer, it doesn't sport the quick shift focusing system.

Pentax SMC DA 40mm F/2.8 Limited Pancake Lens Verdict

With this lens being very similarly specified to the newer XS lens, it can make the price premium difficult to justify, especially as the newer lens is sharper towards the edges of the frame at maximum aperture.

Areas where this Limited lens holds its own include its resistance to flare, build quality and handling. The materials used in the construction and focusing speeds are both superior to the newer lens. The materials used in this lens' construction feel of a higher grade and the design of the manual focusing ring makes the lens easier to use.

It seems that as there is so little to choose between this and the XS lens, those looking for the best build quality and handling will appreciate the difference. Those just after a pancake lens sporting high levels of sharpness across the frame may not.


The Pentax SMC DA 40mm F/2.8 Limited lens is thin and lightweight, with excellent image sharpness

Pentax SMC DA 40mm F/2.8 Limited Pancake Lens Pros

Excellent sharpness from maximum aperture
Thin and lightweight
Good build quality and handling
Fast focusing

Pentax SMC DA 40mm F/2.8 Limited Pancake Lens Cons

Not as sharp as the newer XS lens towards the edges of the frame at maximum aperture



Pentax SMC P-DA 40mm f/2.8 Limited Specifications

Lens Mounts
  • Pentax K SMC-DA
Focal Length40mm
Angle of View0 - 39
Max Aperturef/2.8
Min Aperturef/22
Filter Size49mm
35mm equivalent60mm
Internal focusingNo
Maximum magnificationNo Data
Min Focus40cm
Box Contents
Box ContentsNo Data

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