I was out testing the Canon 40D on difficult moving subjects - feeding ducks, walking 100 yards up the river, feeding them again and making them keeping taking off and landing. I took my Alpha 100 along fitted with the 70-210mm 'beercan' f4, the Canon was fitted with the 70-200mm f4 IS USM L. Both cameras were set to ISO 400, program, continuous focus, motordrive (Canon at 6.5fps, Sony at 3 fps). I didn't have much luck framing and getting sharp focus with the Canon, and didn't use the Sony until I had finished. To my considerable surprise, the A100 hardly had any missed focus shots by comparison. I was just trying to catch the birds in the finder (usually only a single shot was framed right) and fire. From the Sony shots, this one came out which I really like - the best shot of the lot. It has been cropped because a third duck's tail was sticking into the frame in front of the pair. I've warmed up the colour in raw conversion to look more like the evening light it was.

I am surprised. The 70-200mm f4 from 1985 seems to be able to follow focus and lock dead on most of the time. It was less prone to hunt than my 70-200mm f2.8 SSM lens - it never once tracked back to 1.1 metres, though it did focus on the river instead of the bird a few times. It was also very sharp indeed. I do not use this lens at all. I may reconsider. I thought it was old and slow, but it doesn't seem that way.