Conclusion - Pros
- Compact and lightweight
- High quality aluminium construction
- Quick shift manual focus system
- Built-in sliding hood (but see below)
- Good flare resistance
- Almost no distortion
- Small 49mm thread, doesn't require slim filters
Conclusion - Cons
- Rather soft at F4 - F5.6
- Hood design causes problems with filter use (particularly square systems)
The Pentax smc DA 15mm F4 ED AL Limited is a unique lens in the current market, a small, lightweight wideangle prime for APS-C cameras. And let's make it clear from the outset that Pentax should be applauded for producing such a lens, to provide a genuine alternative to the wideangle zooms which are the only option in other manufacturers' lineups. This is indeed typical of the company's attitude towards primes in general; it makes arguably the best APS-C optimized set currently on the market, which counts as something of a selling point for the K system as a whole.
The 15mm is not a bad performer, either. Chromatic aberration is reasonably under control (and easy to correct if necessary), falloff is low at just 1.3 stops wide open, and rectilinear distortion is essentially absent. Also important in real-world shooting is the fact that the lens is very resistant to flare when shooting into the light, an especially desirable characteristic for a wideangle optic. Unfortunately though it's rather soft wide open, and even when stopped down is never breathtakingly sharp in the fashion we'd hope for from a premium prime. This is a little disappointing, especially considering the price and relatively slow maximum aperture; but then again you rarely have to shoot a lens this wide at F4 anyway (especially with the in-body stabilization in all current and recent Pentax DSLRs).
One positive aspect not to be overlooked though is Pentax's signature 'Limited' build quality, which is excellent. The machined aluminium barrel, engraved markings and smooth focus ring may have no effect on the final image, but they certainly make the lens a more desirable object in its own right, and one which is a pleasure to use. The sliding lens hood, of course, will have a genuinely positive impact on image quality, and the fact that it's built-in makes it much more likely to be used as a matter of course. Thankfully the metal construction doesn't result in excess weight, and the lens is eminently portable, making it ideal if you don't want to deal with the bulk of a wideangle zoom.
There are some issues with filter usage, which is something of a double-edged sword. On the plus side, polarizer fans can use standard 49mm filters, rather than the 77mm slimline types required by most wideangle zooms. This can easily amount to $100 difference in price, which is not to be overlooked. However filters can have something of a tendency to bind in place on the lens (presumably due to its aluminium thread), at which point removing them can become a frustrating battle, as the retracting hood impedes your grip. If you do use a polarizer you'll also find yourself spending a lot of time sliding the hood to and fro, to gain access to the filter and adjust its angle. The other problem is that the hood protrudes past the thread when fully retracted, which will cause problems with square filter systems and therefore neutral density gradients - the other most useful type when shooting with wideangle lenses.
The real problem for the 15mm F4, though, lies in the competition, and specifically Pentax's own 12-24mm F4 zoom. This has much in common optically with the Tokina AT-X PRO SD 12-24mm F4 (IF) ED, which we tested recently and found to be a superior performer in almost all regards. It's simply much sharper than the 15mm F4, especially wide open, and exhibits lower falloff and equally low distortion (although it does suffer more from chromatic aberration). It's not often a zoom lens can outgun a prime in terms of image quality, but that certainly seems to be the case here, and by a surprising margin too. At current prices at least you also pay relatively little extra for all the flexibility of the zoom (but do bear in mind the 12-24mm is a well-established product, and the 15mm brand new, so its price is likely to fall over time).
So overall we have a lens which is difficult to categorize. Its very uniqueness makes it desirable - if you want something a bit wider than the 18-55mm kit lens, but without the bulk of a wideangle zoom, it's your only choice. Like all of Pentax's Limited series primes, it's also a finely crafted piece of kit which is a delight to use - a somewhat frivolous reason to choose one, perhaps, although still perfectly valid in its own way. Shot carefully stopped-down to its sweet spot, it also delivers very good but not outstanding image quality. So if your priorities lie in keeping your kit small, light and discreet, it's a great option, but for most users we can't help but feel that a wideangle zoom still makes more sense. Ultimately when compared to the alternatives, the 15mm F4 falls just short of offering enough of the expected advantages of a prime (smaller, faster, sharper, and cheaper) to earn our highest recommendation.
Rating (out of 10)
|Ergonomics & handling||8.5|
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