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

zorgon wrote:

This is a complex thing to compare. The 55-250 might look sharper in 100% pixel view, but it can not capture the detail of a 400mm lens in focal-length-limited situations, so while the 55-250 might get more detail at shorter focal lengths, 250mm can never get more detail than the 400mm can in optimal situations, unless the 400mm is toy-lens quality

I couldn't agree with you less. Toy lens quality is exactly what you get from 3rd party telephoto lenses from that era. I haven't used that lens in particular but have used similar lenses and quality is just atrocious.

Actually you don't agree or disagree with me, because I never made a value judgement on the Tamron 200-400, and my statements were clearly conditional. Words like "and", "if", "but", "when", "until" "still", "unless", etc, present quandaries, but some folks insist on reading sentences with them as if they weren't there and the sentences were absolute statements.

I have no idea how sharp the Tamron 200-400 is, but the fact is, it will get you less subject noise at the same shutter speed in FLL (focal-length-limted) situations because of the larger aperture, even stopped down to f/8 (if the t-stop factor is not much greater for the Tamron). If you have to crop it real hard, of course, and it is very dull at the pixel level, then you will not benefit as much from the lower subject noise, but if you are filling your frame well and you present the image at a modest size, it will have significantly less noise than 250mm cropped, both at f/5.6. Large apertures mean something, even on softer lenses.

From the examples someone else posted, the Tamron seems to have very nice bokeh (not important for airplane shooting, of course).