Is Tamron 200-400mm f/5.6 LD a worthy upgrade?

photonius wrote:

Actually, the new Tamron 150-600 VC is even cheaper, and has IS (VC), and it is a good lens.

It's IS is best for still shooting at low shutter speeds, though; people often find that it doesn't work as well for panning, especially at low shutter speeds where you want to blur the background, in which case turning off the IS and just using a faster shutter speed may be better.

The tests on FF usually compare it to the Canon 100-400 mark I in quality.

Of course, you really have to compare like to like. Sure, the Tamron is softer at 600mm than the 3 Canon 400/5.6 lenses wide open, but they are
only 400mm, and can not capture detail that the Tamron can capture, albeit at a slightly reduced contrast. The Tamron gets significantly sharper wide open at 500 and lower, peaking to an extremely sharp lens somewhere at or slightly above 300mm. The Tamron is about as sharp as a lens needs to be with 4.2 micron pixels at 400/5.6; the IS and AF work very good at 400mm, as well (AF speed drops off above 500mm or so, especially on f/5.6-AF cameras.)

At 600mm the quality drops , can be compensated a bit to go to f8. It should do quite nice on a 40D, which does not have such a high pixel density.

I see it more as the fact that the lower pixel density throws away real detail, losing much of the ability to appreciate a sharper lens. On my 3.1MP Canon D30, the range of f/6.3 to f/11 looks pretty much equal in sharpness in 100% views. The bigger the pixels, the more advantageous it is to use a TC instead of a crop, if it does not interfere with AF needs.

Alas, still around 1000 $, but probably the least expensive tele lens worth spending money on.

Despite its minor weaknesses, it is a great lens for its price. I would highly recommend it to anyone who can only afford $1100 and needs a long zoom. The 400/5.6 might be a better choice for some shooting, though, like BIFs, and its price (especially used) is probably dropping because of the new 100-400 II, which bests it in just about everything, except weight and possibly bokeh. It would be nice to see some worst-case bokeh comparisons between all of these lenses.