One of the great things about the Pentax system is that every bayonet mount lens ever made by Pentax (going back to 1975) can still be used with a high degree of functionality on the most modern Pentax SLR. These lenses can be focussed manually, and used in aperture priority automatic exposure. (Nikon is the only other brand which has allowed its older lenses to be used on modern autofocus cameras, but generally with less metering capability then Pentax.) Hence, it is worthwhile keeping track of the tests of the older lenses.
There are many well-known shortcomings to lens tests, but nevertheless they do give a useful indication of the approximate ranking of a lens along the quality scale. Modern Photography magazine used to report resolution tests on several different lenses in almost every issue, and I found a local university library that has a nearly complete collection of these.
In the Modern Photography tests, there were a couple of cases of what had to be either bad test results or serious typos. One of these was for the Pentax-F 50mm f/1.4. The test showed a string of 98's for resolution, while the written comments said that it was "slightly above average.
Pentax autofocus cameras even provide focus confirmation when used with older manual focus lenses: a green diamond lights up in the viewfinder to indicate the point of correct focus. In the first generation autofocus bodies, the SF series, there was even an arrow that showed what direction the focus ring should be turned in manually to attain focus.
Pentax Lens along with Nikon has been a mainstay of the photographic imaging market as long as it has been a consumer market. That trend continues today with the advent of the digital SLR.
As the consumer becomes more informed and want to have better image quality and they yearn for more creative control over the process than they can get from the standard point and shoot cameras they turn towards the SLR, which stands for single lens reflex. A fancy moniker that basically means that the same lens that feed the viewfinder also feed the camera so what comes in and what you see is precisely what you get.
The Pentax Lens has always been an industry standard for quality optics. The bottom line in photography is that your final image is only as good as the glass in the lens. They lens with great quality glass allows a bright image to be rendered with less ambient light so you can get a clearer image with less grain in much lower light than you can if you use an all in one camera.
Another advantage of a Pentax Lens for a digital SLR is that you are not stuck with only one lens that does ok on most things but does not excel at any of them. If you are far away from an object, you can add a larger telephoto lens and be able to zoom right in. If you are looking for a final image that is wider you simply put on a wide-angle lens and there you have it.
Many zooms produce excellent results, nearly indistinguishable from that of prime lenses, at f/8 or f/11.However, this smaller aperture requires either slower shutter speeds, or restricts their use to fast films or bright sunlight.In the table below, the aperture at which the lens reaches its maximum resolution is noted.
Your Pentax Lens is also designed to accept threaded filters. That allows you to enter the realm of special effects that is actually printed right on to the image. Many photographers, even the pros, now shoot without filters and worry about using software programs to add whatever special effect they were after or envisioned.