Note: I only review lenses that I own and have used for at least one year. This is not a technical review measuring things such as resolution and distortion; I instead concentrate on how the lens handles in regular, everyday use. Also, because I work primarily in black & white, I will not comment on how the lens renders colors.

In addition to their regular line of lenses, Pentax also offers two premium lens lines: the Star series, and the Limiteds.

The Star lenses feature superb optical performance along with rugged construction that is dustproof and weather-resistant. The Limited lenses, however, are a bit different. They have excellent optical performance that can often rival that of the Star lenses, but their primary emphasis is on compact size and unusual focal lengths. This makes the Limiteds unique and distinctive lenses.

Note that the name "Limited" does not refer to the availability of the lens. The Limited lenses have normal production runs and are always readily available.

The SMC Pentax DA 15mm f/4 Ltd is quite a compact lens. The chart below compares the 15mm with four other currently available lenses of similar focal lengths. As you can see, the 15mm is much smaller and lighter than any of these other lenses, and it uses the relatively tiny 49mm filters rather than the large 77mm filters. (The Samyang 14mm's highly curved front element precludes the use of normal screw-in filters.) None of the lenses on this chart are weather-sealed, and none of them have built-in autofocus motors (the Samyangs are manual focus only).

This small size provides a couple of significant benefits. First, you can almost always find room in your camera bag for this lens, so you can always have a wide-angle lens with you. Second, this diminutive lens is non-intimidating. With it you can shoot candids at events such as parties or street fairs without drawing much attention to yourself; try the same thing with a big lens and people can quickly become apprehensive. And, of course, a small, lightweight lens will be easier to handle than a bigger, full size lens.

This lens has excellent center sharpness. The corners, however, are not quite as sharp, which is the only real weakness of this lens. It also has outstanding flare control: if you like to include the sun in your images, this is your lens.

With a 15mm focal length (equivalent to 23mm in full-frame) this lens can be used for street photography, although personally I find it a little bit too wide for this. Pentax has another Limited, a 21mm f/3.2 (equivalent to 32mm in full-frame) which is even smaller than this 15mm that would probably work better for street photography.

You can override the autofocus at any time just by turning the focusing ring; there is no need to switch the camera body back to manual focus mode. The autofocus mechanism is driven by a motor in the camera body itself, rather than by a motor built into the lens. Using the camera's autofocus motor is slower and louder than using a built-in motor, but because this tiny lens has such a short focus throw the autofocus works quite well.

This lens as a built-in, retractable lens hood. This insures that the hood will never get lost, and it takes up no extra room in your camera bag. However, the lens hood does not retract completely, so it will prevent the use of some accessories. Polarizing filters with a knurled ring for rotating the filter, and any accessory that requires a step-up ring, will not work with this lens. A work-around would be to put a 49mm UV filter on the lens and then attach other accessories to that, but you would risk vignetting, and possibly a loss of sharpness from an extra layer of glass.

The lens comes with a metal, screw-in lens cap that protects both the lens and the retracted lens hood. Some people find it too fiddly and replace it with a clip-on lens cap, but it works fine for me.

There are two versions of this lens. The original version (the one I own) with SMC coatings, now discontinued, and the current version with HD coatings and rounded aperture blades. Comments from people who have used both versions indicate that the HD version has slightly better flare control, while the SMC version has better starbursts.

The Pentax 15mm Ltd can be purchased with either the traditional black barrel, or a cool silver barrel. It's an excellent compact wide-angle lens for anyone who doesn't need extreme sharpness in the corners.