Pentax DA 40mm f/2.8 XS Pancake Lens Review

Gary Wolstenhome reviews the Pentax DA 40mm f/2.8 XS pancake lens which was released with the Pentax K-01 camera.

| Pentax DA 40mm f/2.8 XS in Interchangeable Lenses

Handling and features
Pentax DA 40mm f/2.8 XS Pancake Lens Review: Pentax DA 40mm f/2.8 XS

This compact pancake lens, released with the Pentax K-01 camera has a bright maximum aperture of f/2.8 and is currently the thinnest interchangeable fixed focal length lens compatible with an APS-C format camera, being under a centimetre thick.

Pentax also offer another 40mm pancake lens in their limited series. The DA 40mm f/2.8 Limited is a little larger and heavier and can be picked up for around £300.
Pentax DA 40mm f/2.8 XS Pancake Lens Review: Pentax DA 40mm f/2.8 XS

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

The slender lens body of this 40mm pancake lens is constructed from high quality plastics and protrudes just 9.2mm from the lens mount, which is made of metal. At only 52g in weight, it is the perfect accompaniment to either the Pentax K-01 camera, used for testing, or any of the more compact SLRs from their range.

Focusing isn't performed internally (you wouldn't expect this from a lens so thin), but the filter thread does not rotate, making it perfect for use with graduated and polarising filters. The 27mm filter thread size is quite a common size for camcorders, so it shouldn't be too difficult to pick up accessories to fit. A thin manual focusing ring rotates during auto-focus, so care may need to be taken not to catch fingers on it as it spins back and forth. This ring is reasonably well damped and feels smooth to operate.

Auto focus speeds aren't lighting quick, plus as it is a screw-driven focusing mechanism, it makes a fair bit more noise than the newer silent lenses many have become accustomed to. A rubber lens cap is supplied, but as it is only held in place with friction, it tends to fall off easily.

The minimum focus distance of 40cm is fairly typical for pancake lenses. The maximum magnification of 0.13x means this lens isn't best suited for frame filling close-up images.
Pentax DA 40mm f/2.8 XS Pancake Lens Review: Pentax DA 40mm f/2.8 XS

Pentax DA 40mm F/2.8 XS Pancake Lens Performance

Sharpness is excellent in the centre from maximum aperture, and very good towards the edges. Stopping the lens down improves clarity across the frame further, with peak quality across the frame being reached between f/8 and f/11, where sharpness in the centre is outstanding, and approaching excellent levels towards the edges.


Pentax DA 40mm f/2.8 XS Pancake Lens Review: Resolution @ 40mm
Resolution @ 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-01 using Imatest.

Levels of chromatic fringing are within acceptable levels at wider apertures, but the amount of CA towards the edges of the frame increases as the lens is stopped down. At apertures of f/11 and beyond, CA levels exceed one pixel width, which may pose issues for images with high contrast edges towards the outer limits of the frame.

Pentax DA 40mm f/2.8 XS Pancake Lens Review: Chromatic aberration @ 40mm
Chromatic aberration @ 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-01 using Imatest.

Falloff of illumination towards the corners is well controlled for a lens of this type. At f/2.8, the corners are only 1.06 stops darker than the image centre. Visually uniform illumination is achieved with the lens stopped down to f/5.6 or beyond.

Barrel distortion is slightly high for a fixed focal lens. Here Imatest detected 3.56% barrel distortion, which shouldn't pose too many issues for general photography, but may be too strong for work where straight lines are critical. Luckily the distortion pattern is uniform across the frame, so this distortion should be relatively easy to correct in image editing software.

Pentax DA 40mm f/2.8 XS Sample Photos

No lens hood comes supplied with this lens, and for the most part it is reasonably resistant to flare. When shooting in very harsh backlit conditions, flare can be an issue, and image contrast drops off considerably.

Pentax DA 40mm F/2.8 XS Pancake Lens Verdict

Obvious benefits of a pancake lens like this are the compact size and lightweight, but this lens delivers excellent sharpness too.

The issues with flare and high CA levels when stopped down may be off-putting to some, but if care is taken to use this lens within its limits, it can deliver excellent quality images, without the bulk of a normal Pentax K-mount lens.

This basic, but compact lens could be the ideal lens for Pentax shooters wishing to travel as light as possible.


Pentax DA 40mm F/2.8 XS Pancake Lens Pros

Excellent sharpness from maximum aperture
Thin and lightweight
Good build quality
Vignetting is well-controlled

Pentax DA 40mm F/2.8 XS Pancake Lens Cons

High CA levels towards edges of the frame when stopped down
Loss of contrast and flare when shooting into the light
Rubber lens cap falls off easily


Pentax DA 40mm f/2.8 XS Specifications

Lens Mounts
  • Pentax K
Focal Length40mm
Angle of View39°
Max Aperturef/2.8
Min Aperturef/22
Filter Size27mm
35mm equivalent61mm
Internal focusingNo
Maximum magnificationNo Data
Min Focus40cm
Box Contents
Box ContentsLens Caps

View Full Product Details

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morelia Avatar
morelia 14
28 Mar 2012 5:03PM
I wonder how it compares with the excellent Pentax smc DA 40mm f/2.8 Limited lens?
Offertonhatter Avatar
28 Mar 2012 11:22PM
I was thinking the same thing Morelia. What will be interesting will be the street price of the lens (as opposed to the RRP of £300), as Pentax could be onto a winner here by introducing people to the joys of pancake lenses, with the hope of further investment down the line of 21mm and 70mm purchases.
I think it probably has about 80% of the 40mm Limited, missing out on the beautiful metal build, dedicated hood and ability to put 49mm filters or filter adapter ring on the front.
Personally I won't be buying it, as I have just got the 40mm Limited myself (yesterday) and so far it is a stunning lens. If this has the same optics (probably) people who buy it won't be disappointed on the whole.

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