The smc DA 15mm F4 ED AL Limited is Pentax's latest lens, which was shown in prototype form at Photokina 2008 and formally introduced in March 2009. It's a rare beast indeed: a wide angle fixed focal length ('prime') lens that is purpose-designed for APS-C format digital SLRs. The 15mm focal length gives an angle of view equivalent to a 22.5mm lens on the 35mm format; in essence, this lens is the modern equivalent of old favorites such as the 24mm F2.8 or the 21mm F3.5. The 'Limited' tag denotes premium construction, with the lens barrel made entirely from high-grade aluminium, which comes as a refreshing change from the engineering plastics used almost universally by other manufacturers.

As a fixed focal length lens, the 15mm is much smaller and lighter than zooms with a similar angle of view, and requires rather simpler optics as well. The formula uses 8 elements in 6 groups, including one hybrid aspherical element and one extra-low dispersion (ED) glass element, which combine to minimize distortion and chromatic aberrations. Other key attractions of the design are the 'quick shift' focus system, which allows manual adjustment even when the camera is set to autofocus mode, and a clever built-in sliding petal-shaped hood.

In a market dominated by identikit zooms, it's certainly refreshing to see Pentax offering a genuine alternative, and catering to users who value the advantages of prime lenses over the undoubted flexibility of zooms. However the rapid advance in computer-aided lens design, coupled with manufacturing technologies such as glass-moulding for the inexpensive mass-production of aspheric elements, means that the once-yawning gulf in image quality between primes and zooms has narrowed considerably over the past decade. So the question is, does the 15mm F4 still have enough on offer to make any practical sense?

Headline features

  • 15mm wideangle focal length, F4 maximum aperture
  • 'Quick Shift' system allows manual adjustment of focus in AF mode
  • Built-in sliding petal-shaped lens hood
  • High quality aluminium construction

Angle of view

The picture below illustrates the angle of view (click here for comparison shots with the 18-55mm kit lens):

15mm (APS-C format)

Pentax smc DA 15mm F4 ED AL Limited specifications

Street price • $600 US
• £750 UK
Date introduced March 2009
Maximum format size APS-C
Focal length 15mm
35mm equivalent focal length 22.5mm
Diagonal Angle of view (APS-C) 86º
Maximum aperture F4
Minimum aperture F22
Lens Construction • 8 elements/6 groups
• 1 Hybrid aspherical element
• 1 Extra-low-Dispersion (ED) glass element
Number of diaphragm blades 7
Minimum focus 0.18m
Maximum magnification 0.15x
AF motor type • 'Screw drive' from camera body
• 'Quick shift' manual focus system
Focus method Unit
Image stabilization Via camera body
Filter thread • 49mm
• Does not rotate on focus
Supplied accessories • Front and rear caps
• Soft case
Weight 212g (7.5 oz)
Dimensions 63mm diameter x 39.5mm length
(2.5 x 1.6 in)
Lens Mount Pentax K

* Supplied accessories may differ in each country or area