The longer the focal length, the bigger the lens. And if you need a 500mm lens (800mm equivalent when fitted to a digital SLR), you can’t expect it to fit in the average gadget bag.

To its credit, the Tamron 200-500mm is pretty compact for a lens of this range. While it’s quite long at 227mm it's also slim, only flaring out slightly at the front end. Interestingly, Sigma’s 50-500mm is a lot fatter, but a lot shorter. It also remains a good deal shorter when both lenses are zoomed all the way out to 500mm.

The Tamron is a much ‘sweeter’ lens to use, and the focusing movement is light and smooth where the Sigma’s is stiff and variable. The Tamron’s manual focus ring is similarly smooth, though the travel is quite short.

Like all long lenses, this one has a rotating tripod bracket which can be removed, though with this type of lens there’s the constant risk of camera shake if you attempt to shoot handheld. The tripod bracket seems perfectly positioned – with a reasonably lightweight body attached, it’ll sit on a flat surface without overbalancing.

Like other Tamron zooms, this one has a ‘Lock’ switch on the barrel. This stops the barrel moving in and out when the lens is being carried – there’s not much tendency towards zoom creep with this lens, but if you jar it while walking or running, the barrel will slowly work its way out.

The performance of this lens in our resolution tests was higher than we’ve come to expect from long zooms of this type. The resolution holds up very well, even at the maximum focal length. It drops sharply at smaller apertures, but this may be due as much to the difficulties of testing extreme focal lengths like these as it is to any optical fall-off. At these magnifications, people walking along a corridor or even traffic passing outside can introduce vibrations that compromise the sharpness, and with the longer exposures needed for testing at small apertures, external vibration becomes an increasing problem.

There is some noticeable red-green chromatic aberration (colour fringing) at the edges of the frame at maximum focal length, but in lenses of this range something’s got to give eventually, and at least it’s not outright definition. This is where the Tamron really justifies its weight and its price – it maintains high sharpness right across the focal range, which is pretty uncommon in zooms.

There’s no image stabilisation on this lens, but most users are likely to have it fixed to a tripod or a monopod, where this is far less of an issue. The balance is also very nice, and with the tripod bracket removed it is possible to handhold it for ‘panning’ shots and others that need to be taken ‘on the hoof’.

The Sigma 50-500mm zoom offers similar quality and a wider zoom range, but it’s not so nice to handle and a good deal heavier.

The Tamron’s build quality is as good as its optical quality, so the £830 SRP isn’t too big a surprise. However, if you shop around you can get this lens for a lot less, and it undercuts any comparable marque lens from Canon or Nikon.

Final Verdict A super-long lens that maintains a high performance even at full range. Highly recommended for wildlife fans OVERALL

Our lens reviewer, and technical expert, Rod is a veritable photographic encyclopaedia. His illustrious CV has seen him write for many mags, websites and journals.