The Pentax smc DA 55-300mm f/4.0-5.8 ED is an impressive tele-photo zoom with much to admire about it
Most notable is the 5.5x zoom range, which covers the same angles-of-view as a full-frame 82-450mm lens. The maximum aperture drops from f/4.0 to f/5.8 as the focal-length increases but this is not an unreasonable contraction. In fact f/4.0 is maintained down to 100mm and the camera only just indicates a decline from f/4.5 to f/5.6 at 200mm. Similarly, the minimum aperture is f/22 down to 100mm and f/32 thereafter.
The lens barrel is dominated by a very wide and prominently textured zoom ring, in front of which sits a much narrower manual-focussing ring. The MF ring rotates in AF mode but is fairly-easily avoided yet at the same time is within reach to make any manual adjustments, which can be applied in AF mode. The MF ring has a distance scale but there are no depth-of-field markings.
A cylindrical lens hood is provided together with a soft carrying pouch. The hood has a removable section that allows polarising filters to be rotated in-situ. Reversing the hood for storage hides the MF ring completely but leaves enough of the zoom ring exposed for emergency use so that unexpected pictures can be grabbed with a minimum of delay.
The AF system is somewhat noisy but that is the only disappointing aspect of this lens. Audibility aside, focussing in AF mode is quick and accurate.
Technical testing revealed a good set of MTF curves that not only bettered the important 0.25 cycles-per-pixel threshold but also reached or exceeded 0.3 cycles-per-pixel for all four focal-lengths tested. There was some unwelcome chromatic aberration at the wider end of the zoom range and again at the maximum setting but at 200mm the image quality was exceptional clean. Bearing in mind that this is an affordable lens with a greater than 5x zoom range, those results are very good indeed.
There are some obvious omissions from the 55-300mm lens, such as full-frame coverage (for film-camera compatibility), internal focussing and image stabilisation but the first is acceptable, the second is not critical owing to the zooms overall design and the third can be provided through Shake Reduction on the host body. Balancing these wants, Pentax claims that its new and exclusive Super protect (SP) coating provides even greater protection than previously for the front element against dirt.