How good is YOUR lens?

We chose a lens that has a good reputation and asked the manufacturer to supply one. We then sourced two more lenses of the same mark from ePHOTOzine members (many thanks to them). The lens of choice was the Canon 100-400mm L IS, you know the one, the big white zoom!
We shot a frame at each full aperture stop (Except f/4.5 at 100mm) at each of three focal lengths, 100mm, 250mm and 400mm.

Please note that the figures achieved here are from a 4.2mp camera with a 1.3x crop factor. The same lens on a different camera is likely to produce different results. That is because, unlike in the old days when you could put the same type of film in different cameras, with digital every different camera has a different sensor (See Making Sense of Sensors)

As you can see from the graphs (higher numbers are better), there was considerable variation between the lenses, although they all proved to be better at the short end than at the long end and all peaked in their performance at around the same figures.
Although there would appear to be a clear winner out of the three examples, the one with the best looking figures has consistently caused lock-up problems on at least three different bodies, whereas the other two have not caused any known problems. One has never been serviced and the other has probably been serviced regularly, as it belongs to Canon. The Canon lens, incidentally, has the earliest serial number! In practice, they all produce excellent pictures.

It does, however, show that the variation in equipment reviews is not down to bias by the reviewers, or not entirely anyway. The tolerance range in the manufacturing process is certainly a little larger than we would have expected from a top end lens, so it will be interesting in the future to try comparisons of the same kind on other marques. Watch this space.

Review by Ian Andrews