Helios68 said:
Canon's f/4 familly is really wide: 70-200mm, 300mm, 400mm, 500mm, 600mm
The f/2.8 is not to bad: 70-200mm, 300mm, 400mm.
Stopping at 400mm f/2.8 makes sense : price and weight are not really interesting anymore for longer focal.
But the f/5.6 is not well represented: 400mm then 800mm. There is a lack in 500mm and 600mm
This is not really the best way to think of it. A 200 mm f/2.8 is a fairly ordinary lens, but a 400/2.8 is a dream supertele and a 600/2.8 would be gigantic. Putting all the f/2.8 lenses into one category doesn't work.
A more useful split is this:
- 70-200/4, and also the 70-300L which you didn't mention, are the smallest both physically and optically.
- Next category up includes the 70-200/2.8, 300/4, 100-400/4.5-5.6, and 400/5.6. All broadly in the same size/weight/optical size and price bracket. We probably ought to include the 200/2.8 prime, which is an old lens and unusually cheap.
- Then the 200/2, 300/2.8, 400/4 and 500/4. The 400/4 is slightly expensive for its size, because it's a DO lens, but we can include it in the same group. These are the slightly more affordable of the 'big whites'.
- Finally two monsters, the 600/4 and 800/5.6.
If you work out the entrance pupil size, which is basically the same as the front element size for a long lens, you'll find they are clustered together. The first group is 50-54 mm; the second is 72-75 mm; the third is 100-125 mm; and lastly140-150 mm.
I think this is a very sensible structure, giving us a choice of small, medium, large and huge.
So where does a 500/5.6 fit into this? It doesn't really, it falls between two stools. It is neither as affordable and portable as the 300/4 and 400/5.6 lenses, nor is it is powerful as the 300/2.8 and 500/4. I guess it would have to cost around £3000-£3500 which is probably too much for most 100-400L customers, but those who can afford more will mostly want the 300/2.8 or 500/4. I'm generalising of course.
On the other hand, Sigma and Tamron have chosen to drop their lenses right into the gap, and by doing so they have found a sweet spot for birders and other keen amateur wildlife photographers. The burning question is, will Canon ever do the same?