Pentax, as one of the major single-lens reflex camera manufacturers over the last 60 years, has made a variety of lenses for a variety of uses. Pentax introduced the pentaprism that allowed the creation of the SLR camera by bouncing the incoming image off a mirror into the pentaprism. The pentaprism then corrected the image left to right and turned it right-side up for normal viewing. The innovation led to an expansion of the types of lenses available for the photographer's use.
Basics
Basically, Pentax lenses have ranged from extreme wide-angle, also called fisheye, to extreme telephoto with many focal lengths and zooms in between. There also are special-use lenses such as macro, which allows the photographer to get extreme closeups such as a bee on a flower. Each lens has specific intended uses, but also can be used for all types of photography.
Fish-eye
The smc (super multi-coated) Pentax DA 10-17mm F3.5-4.5 ED (IF) Fish-Eye lens has a 180-degree field of view, meaning from horizon to horizon. While this lens can be used for landscapes, in industrial settings and for artistic reasons, as the company proclaims, the cost to the photographer is distortion. The only way to get that field of view is to distort or bend the lines of reality to make them fit. So while it will get you extraordinary scope, it's not a good lens for portraits because it will take an unflattering and bent image of your subject.
Wide Angle
The smc Pentax DA 12-24mm F4 ED AL (IF) lens is the widest-angle lens available for the Pentax camera line. Since it is intended for use on digital cameras that have a 1.5x multiplication factor, that puts the lens at 18-36mm zoom, but still quite wide. It does not distort the image field like a fish-eye lens, so it is good for shooting large groups of people and room interiors as well as outdoor landscapes. It also can be used in architectural and aerial photography. For a twist, turn the camera vertical next to a tall building. Pentax also has a variety of other wide-angle lenses, including the wide-range smc Pentax DA 18-250mm F3.5-6.3 ED (IF) lens that goes from wide-angle to long telephoto.
Telephoto
Telephoto lenses, such as the smc Pentax DA Star 300mm F4 ED (IF) SDM, is good for shooting at long range, such as at sporting events and concerts. On a digital camera multiplied by 1.5x, that's 450mm. If you add a 2x extender, you can get up to 900mm. There will be considerable light drop off at the focal length, but shooting outside on a sunny day, 900mm will get you right into the action. Pentax also makes the smc Pentax DA 55-300mm F4-5.8 ED telephoto zoom that can still get to long telephoto, but can come back to normal.
Specialty Applications
Short telephoto and macro lenses each have their own specific uses, too. The smc Pentax D FA 100mm F2.8 Macro can serve both of these. You can focus close to get that bee hovering above the flower or the hummingbird at the feeder. You also can use it as a short telephoto for portraits. Short telephotos make good portraits because they allow you to focus on the subject and move everything else into a soft-focus around her. For example, if you position your model in front of bright, red roses, the roses will provide a dreamy, soft focus backdrop to frame her face and features.
Tags: also used, field view, good shooting, lenses such, long telephoto, Pentax also