Pentax’s new pancake lens falls flat

Thursday June 07 2012

Pentax’s new pancake lens falls flat

The new lightweight smc Pentax-DA 40mm f/2.8 XS strives to be a versatile weapon in a photographer’s arsenal of lenses.  But the dainty lens, weighing only 51 grams and measuring a slim 9mm in thickness, needs a little more beef – at least that’s what DxOMark determined after putting the lens’ optics through our rigorous tests.

World renowned industrial designer Marc Newson threw his name and his imagination behind one of Pentax’s latest lenses. Newson’s twist on the exterior of the smc Pentax-DA 40mm f/2.8 XS lens has given it the appearance of a black poker chip.

But Pentax’s gamble with the XS redesign didn’t extend to the optics found inside its new lens. That was our conclusion during our DxOMark testing, where we discovered there was just a marginal improvement in the XS from its eight-year-old predecessor – the smc Pentax DA 40mm f/2.8 Limited.

Analysis: smc Pentax-DA 40mm f/2.8 XS lens performance using Pentax K-5

The ultra-compact and circular XS lens, weighing a dainty 51 grams and measuring a slim 9mm in thickness, scored only 12 points in our DxOMark scale (see below for full score results) when tested using the Pentax K-5, a 16.3-megapixel digital SLR.

Despite its weak score, the lens succeeded at:

  • Limiting distortion.
  • Vignetting – an effect that darkens or reduces saturation at the edges of a photograph – remained low.

The Pentax-DA 40mm f/2.8 XS struggled with:

  • Visible chromatic aberration – an unflattering effect that creates blurring and color fringing, especially where dark and bright points meet in a picture.
  • Softened sharpness and reduced resolution at the center and corners of images when tested at aperture f/2.8. This defect was mitigated when the aperture was set to f/4 and above – it was here that our scientists observed improved image resolution.
Pentax smc DA 40mm f/2.8 XS: resolution maps
Above are resolution maps for the Pentax smc DA 40mm f/2.8 XS mounted on a Pentax K5.  Tested at 40mm focal length and aperture f/2.8 (left), f/4 (center), and f/5.6 (right) you can observe the lens’ resolution begins to improve at aperture f/4 and higher.

Head-to-Head against the smc Pentax-DA 40mm f/2.8 Limited

The XS lens scored only one-point higher than its predecessor.  This is disappointing when you consider Pentax had about eight years to improve the shortcomings of the smc Pentax DA 40mm f/2.8 Limited.

Pentax smc DA 40mm f2.8 XS vs Pentax DA 40mm f2.8 Limited

When comparing image and optics quality against the Limited, the XS was tested as having slightly better brightness – improving about 0.2 T-stop over its older sibling.

Additional strengths of the XS over the Limited include:

  • The f/2.8 XS is a better value, costing about $250.00 (US).  This is nearly half the price of its older sibling.
  • The XS is more lightweight – weighing just 51-grams, and nearly two times lighter than the Limited.
  • Pentax’s newest 40mm lens is also more compact:  the XS is 9.14mm thick compared to the Limited, which is 15mm.

The one weakness of the XS compared to the Limited is its resolution.

  • The Limited has better resolution in the field at aperture f/2.8.