The preference for zoom lenses is partly due to the convenience of not having to carry and change lenses, and the ability to rapidly change focal length for opportunistic shots, which is a boon for photojournalists.
Photographers graduating from compact digital cameras with built in zoom lenses have an expectation of zooming rather than planning and working around a fixed focal length. However there are disadvantages using a zoom, particularly an all in one super zoom lens, of greater size, weight , cost, and poorer optical performance.
But how much poorer? Initially early zooms had a poor reputation for optical performance before computer aided design helped produce quality zooms such as the original Vivitar Series 1 70-210 lens back in the1970s.
Courtesy of DxOMark here is three way comparison of a 50mm prime, or single focal length lens and two zoom lenses. all are Nikon and were tested on a Nikon D300 digital SLR camera.
The overall DxOMark scores reinforce the belief that primes are better optically than zooms. They also illustrate the relationship between image quality and zoom range. The greater the range of focal lengths covered by a zoom the greater are the optical design challenges.
Low Light King
Of course the DxOMark scores are heavily influenced by the wide maximum aperture of the 50mm prime lens. As a class of lenses the fast fifties are often the first choice of photographer’s in low light conditions.
Resolution
Looking at the field map representation of the resolution test results shown below, all were conducted at 50mm and with a similar aperture, the results indicate the prime 50 is sharper, particularly in the center of the image.
Distortion
The Nikkor 18-200m super zoom lens shows distinct signs of pincushion distortion at 50mm focal length, much more than the other two Nikon lenses. Referring to the full DxOMark tests for this lens, they show that this is at the focal length where pin cushion distortion is greatest.
Chromic Aberration
Surprisingly, considering the overall results trends, the Nikon 50mm prime comes out worst for Chromic Aberration at the same f5.6 aperture as the two Nikon zoom lenses. Once again looking a the full DxOMark tests shows the Nikon 50mm prime lens suffers least from Chromic Aberration when the aperture is at f5.6 or wide open. It seems the Nikon designers have optimized their Nikkor 50mm prime for low light photography where photographers will take full advantage of the extra large apertures.
In this case and a this foal length /aperture combination the Nikkor 16-85mm mid range zoom comes out best and still beating the Nikkor 18-200mm super zoom lens.
Price
One of the arguments for the super zoom lenses is that photographers save money buying only one lens to cover all their needs. Depending on the type and amount of photography undertaken it often ends up that only a small number of focal lengths are actually used. The 18mm end of the super zoom zoom is very useful for landscapes and for portraits in crowded places or large groups. At the other end of the scale, 200mm is handy for sports and wildlife. Somewhere in the middle 50mm is ideal for general work, and is a mild telephoto on a dSLR with an APS-C size sensor.
Looking at the comparative prices of the three lenses in the summary table below, the super zoom lens is clearly the most expensive. Depending upon usage requirements, the super zoom lens could be more expensive as photographers are paying for focal lengths they never need.
Convenience
Much is made of the convenience of not having to carry extra lenses, but this can be offset by the size and weight of the super zoom lens. It is double the weight of the 50mm prime and is twice as long.
Flexibility
Here the super zoom lens obviously comes out on top for those occasions where it is an advantage where photographers need to change focal length over a wide range and do it quickly.
One example is photographing horse racing, where all the action happens in the run to the finish post and for many races are less than lap of the course so the horses only race past the photographer once. Here the technique is to use maximum zoom as the horses approach and then zoom out as they get closer, shooting all the time.
The Verdict
The DxOMark tests show the 50mm prime lens is the best optically , particularly in low light situations. It is also easier to carry than the larger and heavier zoom lenses. However, the prime does lack the flexibility of instant changes of focal length required in some situations.
Sitting in between the two extremes of a fixed focal length and the super zoom lens is the Nikkor 16-85mm zoom. as a general purpose lens it outperforms the super zoom lens optically as well as on price and convenience. Its focal range covers most of the popular wide angle for landscapes and groups to short telephoto making it a good choice for general photography.
Of course the advantage of the dSLR system is that for the occasions when you do need something outside the range of the general purpose lens, it is easy to change the lens. This is why serious photographers end up with a collection lenses to suit different situations.
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