I've said it before and I'll say it again: When it comes to making exceptional prime lenses for SLR cameras, few companies rival the quality of Pentax. Not only has Pentax long been famous for making some of the best prime lenses money can buy, but this company consistently makes lenses that most hard-working photographers can afford. One of Pentax's most anticipated new prime lenses is the Pentax DA 15mm F4ED AL Limited.
For those photographers using Pentax cameras and lenses (often referred to as Pentaxians) the arrival of the DA 15mm f/4 Limited lens seemed like only a matter of time. Sure, Pentax already has a 14mm f/2.8 lens, but there's just something special about the DA Limited series of prime lenses with their all-metal construction and compact size. In fact, the new 15mm lens is almost half the size of the older 14mm lens ... making it much easier to carry with you while traveling. When Pentax announced the DA 15mm f/4 Limited lens, I was eager to get my hands on one.
The Pentax DA 15mm f/4 Limited prime is offered only in the Pentax KAF2 lens mount, a modernization of the long-lasting Pentax K mount. With a crop factor of 1.5x on DSLR cameras, the lens has a 35mm equivalent range of 23mm.
What separates the KAF2 mount from earlier versions is the addition of a contact for new lenses with a built-in Supersonic Motor (SDM), which the DA 15mm (like all other Limited lenses) does not employ.
Design and Build Quality
The new Pentax 15mm is a mainly intended as a compact prime lens for landscapes, designed to cover the extreme wide angle focal length similar to an old 20mm lens on a film camera. The filter thread is 49mm and does not rotate on autofocus, which is good for polarizer or gradient filter users.
While we're on the topic of the front filter thread, it's worth taking some time to talk about the unusual lens cap that comes with this lens. Like several of the other "Limited" lenses in the Pentax lineup, the 15mm lens includes a screw-in aluminum lens cap that is lined with felt to protect the front lens element. While screw-in lens caps certainly look cool and give the lens a retro appeal, this type of lens cap is impractical (if not extremely aggravating) to use since you have to unscrew the lens cap every time you want to take a photo.
The DA 15mm Limited isn't some $100 "kit lens" intended for general use. This compact lens has a rugged, all-metal build quality and a price tag to go with it ($649.95). Fit and finish are first rate with the same metal alloy construction found on all Limited series lenses.
The built-in, pullout type lens hood helps shade the front lens element and prevent flare, but I personally would have preferred a fixed lens hood since the hood doesn't make the lens that much larger and does a fantastic job of shielding the front lens element.
Markings (distance scale in both feet and meters) are clear and easy to read and include a basic depth of field scale.
One feature that's worth mentioning is that the DA 15mm Limited lens uses fully automatic diaphragm control: you can't manually select the aperture by turning the diaphragm collar on the lens because there is no diaphragm collar.
Optical construction is all-glass with 8 elements in 6 groups, with Pentax's new Super Protect (SP) lens coating which protects the exposed lens elements. The 7-bladed aperture diaphragm does a fine job for controlling Depth of Field (DOF).
As noted, APS-C style sensors in Pentax cameras have a 1.5x crop factor, so this 15mm lens performs like a 23mm lens. The shorter focal length range makes this prime absolutely perfect as a "landscape" lens for general use or for group shots, indoor photos, or close-up portraits with a unique perspective.
The Pentax 15mm Limited lens is driven by Pentax's traditional in-body focus rather than the in-lens focus system. This typically means focus is a little slower than lenses with their own built-in focus motors, but the DA 15mm Limited is so small and light weight that it still focuses reasonably fast. Considering that the full focus range is from 0.59 feet (0.18 meters) to infinity, the focus ring only has to rotate about 80 degrees ... meaning it doesn't take long to lock auto focus even if the lens hunts for focus.
Focusing manually with the Pentax DA 15mm Limited lens is much easier than with older Pentax lenses. As with all lenses in the DA family, there is no need to flip the MF/AF switch on the lens barrel or camera body because this lens features "quick-shift focus" (full-time autofocus override).
All you have to is point the camera at your subject and turn the MF ring until the subject snaps into focus. You never have to turn off autofocus again in order to adjust manual focus. The manual focusing provides just the right amount of resistance when turning.
The default "bright" color tone setting on the latest generation of Pentax DSLRs produces quite a bit of image contrast, but the DA 15mm f/4 Limited is a little more average in terms of sharpness wide open at f/4. When stopped down past f/5.6 the lens is as sharp as anything in this class. Considering that most photographers will use this lens for landscapes it's safe to assume that stopping down to f/8 won't be a problem.
At the widest aperture of f/4, the DA 15mm isn't quite as sharp but sharpness (or softness) from one edge of the frame to the other is pretty consistent, so you won't have to worry about corner softness with this lens when it's stopped down. The biggest surprise, however, was the virtually nonexistent distortion. Most extreme wide angle lenses suffer from horrible barrel distortion (a type of distortion that causes straight lines to "bend" outward) but the Pentax 15mm lens is virtually distortion free. Again, I cannot stress this enough ... this lens is virtually free of all distortion!
This is an extreme level of quality we're starting to see on a regular basis from Pentax DA Limited primes. The Pentax DA 15mm renders colors that are hue accurate, bright, and nicely saturated. This glass should be more than capable of resolving any detail needed for high resolution digital image sensors such as the newer CMOS image sensors in Pentax DSLRs.
Flare and internal reflections are very well controlled. Chromatic aberration (color fringe around high contrast lines) is also well controlled; we didn't find any color fringing on high contrast edge demarcation areas in our images and had to go out and intentionally "try" to create color fringing in order to see any. Bottom line, this lens has excellent optical design.
Vignetting (dark corners) was negligible at all apertures with and without the hood. The only potentially negative issue with the DA 15mm Limited lens (other than softness wide open) is that the maximum aperture of f/4 doesn't offer much in the way of shallow depth of field. Granted, most people using a wide angle lens want more DOF and not less, but it would have been nice if this lens could have opened up to at least f/3.5 for better DOF control and low light performance.
Although I use multiple camera brands and lenses, I have a special place in my heart for prime lenses from Pentax. Sure, there are modern zoom lenses that cover extreme wide angle, such as Pentax's own 12-24mm F4 zoom or Sigma's 10-20mm zoom, but you will never find a zoom lens that is as distortion-free as the Pentax DA 15mm Limited. The excellent wide angle focal length, resistance to flare and fantastic control over distortion make this a must have for landscape photographers. The 15mm focal length also works well as a portrait lens if you're looking for an interesting perspective on your subjects. As long as you're willing to stop down the lens to a higher aperture you will be extremely happy with the sharpness this lens can provide.
In short, the new 15mm Limited is a fantastic wide angle lens with outstanding control over distortion, great edge-to-edge sharpness when stopped down past f/5.6, and exceptional build quality common to the Limited series lenses. If you're in the market for a wide angle lens, this is a great option.