Prime concern
Zoom lenses aren't the only option. At any given price point, prime (fixed focal length) telephoto lenses often offer wider available apertures, a more compact build, and better overall image quality. The Pentax DA* 200mm is certainly one of the smaller lenses in this test group – and the least expensive, despite having a wide f/2.8 aperture.
By contrast, the Sigma APO 180mm prime is the heaviest and most expensive lens in the group. However, it's a dual-purpose telephoto and macro lens, delivering full 1.0x magnification at its shortest focus distance.
Sensor size and effective focal length
Getting back to the greater convenience and versatility of zoom lenses, 70-200mm is the most popular telephoto range, at least for constant-aperture designs. All five 70-200mm lenses featured in this round up are compatible with full-frame sensors. Being a Micro Four Thirds lens with a 2x focal-length multiplier (or crop factor), the Panasonic 35-100mm has the same effective range as the other zoom lenses when they're mounted on full-frame bodies.
However, when using 70-200mm lenses on cameras with APS-C sensors, you get a boost in effective reach. This is usually 1.5x for most APS-C format cameras, and 1.6x for Canon bodies, resulting in effective zoom ranges of 105-300mm or 112-320mm respectively.
Faster autofocus
All these test lenses have fully internal focus systems, which gives two advantages. First, the front element remains fixed throughout the whole focus travel. It neither rotates nor extends, making it easier to use rotation-specific filters like circular polarisers and ND grads.
Second, because focussing relies on the movement of relatively small inner or rear elements within the lens, autofocus speed tends to be rather faster. This can be a major bonus in sports and action photography, both for rapid acquisition of autofocus and for tracking moving targets in Continuous AF mode.
Features to look for
Prime vs zoom: For sports and wildlife shoots, zoom telephoto lenses do give greater versatility than primes, especially when you're limited to a specific viewing area or taking cover in a hide.
The long view: Constant-aperture 70-200mm lenses have a fairly long physical length of 175-200mm. but wiith internal zoom systems, their overall length stays fixed at any focal length.
Feel the width: For any given focal length, lenses with wider available apertures will have a bigger diameter front element, and a bigger filter size. For 70-200mm f/4 and f/2.8 lenses, it's typically 67mm or 77mm respectively.
Keep it quiet: For wildlife and bird photography, quiet autofocus can be a big help. Ring-type ultrasonic systems tend to be whisper-quiet, whereas stepping motor systems are virtually silent.
Optical stabilization: Nearly all of the lenses on test feature built-in optical stabilization. However, stabilization is omitted in the Pentax 200mm lens and the Sony A-mount edition of the Tamron 70-200mm because they camera's they're designed for have stabilization built into the body.
Included accessories: Every lens in the group comes complete with front and rear caps, carrying pouch and hood. A tripod collar and mounting foot is also supplied with the heavier lenses.
