The Pentax SMC DA 40mm F2.8 Limited, which came out in 2004, is still made by the Nippone company. Ultra-compact and light-weight — 15mm for 90g, this is a true pancake. Thus we find in a very confined space five glass elements and a 9-bladed diaphragm for better rendering of blurry backgrounds.

Note that this is not Pentax’s first try at producing pancake lenses: it’s been doing so since 1976 for its analog cameras. While we wait for the results of its new version, the Pentax smc DA 40mm f2.8 XS, let’s take a look at the optical performance results of the first 40mm pancake designed for Pentax digital cameras.

This 40mm is the full-field equivalent of a 60mm, making it an “all-terrain” general-purpose lens. And as with all lenses in the “limited” category, this Pentax 40mm was carefully built.

Measurements

Pentax smc DA 40mm F2.8 Limited mounted on a Pentax K5

A DxOMark score of 11 is not very good. (The score was derived at f/4 because the resolution over the field drops significantly at f/2.8.) Its best compromise between light and resolution is f/4.

The good points of the Pentax smc DA 40mm F2.8 Limited:

  • Decent resolution starting at f/5.6.
  • Well-corrected distortion.
  • Vignetting “correct” for this kind of lens.
  • Invisible or barely-visible chromatic aberrations.
  • Remarkable compactness.
  • Very light-weight.

The “debatable” points of the Pentax smc DA 40mm F2.8 Limited:

  • The resolution at f/4 and f/2.8 is quite disappointing both over the field and in the center.
  • Lack of brightness.

Comparison

Pentax smc DA 40mm F2.8 Limited mounted on a Pentax K5 vs Nikon AF Nikkor 35mm f/2D mounted on a Nikon D7000

The two lenses have close scores for nearly all the metrics, but with a DxOMark score of 16, the Nikon AF Nikkor 35mm f/2D mounted on a Nikon D7000 is 5 points ahead of the Pentax smc DA 40mm F2.8 Limited mounted on a Pentax K5. The difference in scores is largely explained by the resolution at wide aperture. Whereas the Nikon 35mm f/2.0 maintains decent resolution at f/2.8, the Pentax drops like a stone. The comparison is especially relevant, given that both cameras make use of the same Sony sensor.

The advantages of the Pentax smc DA 40mm F2.8 Limited:

  • More compact.
  • Lighter.

The advantages of the Nikon AF Nikkor 35mm f/2D:

  • Brighter (around 1.12EV).
  • Slightly less vignetting.

See also Nikon AF-D lens reviews

Conclusion

The SMC DA 40mm F2.8 Limited is an extremely light-weight and compact pancake lens that masters distortion and chromatic aberrations well. Nevertheless, its compactness comes at the price of only so-so brightness and a resolution at wide aperture that really could stand some real improvement.

We are very much looking forward having the chance to compare it with the new Pentax smc DA 40mm f2.8 XS, whose measurements on a Pentax K 01 will be available in the not-too-distant future. In the meantime, we can at least compare the specs for both these 40mm lenses:

Pentax smc DA 40mm f2.8 XS vs Pentax SMC DA 40mm F2.8 Limited

We see that Pentax certainly managed the feat of not only of reducing the weight of its 40 mm lens by more than 40g (the weight is nearly divisible by 2), but also in significantly reducing its size (9.14mm for the XS vs. 15mm for the limited). We hope that our upcoming tests will reveal that Pentax will have succeeded in improving its resolution at wide apertures.