Tamron 150-600mm f/6.3

[Dave Throgmartin]

My longest lens right now is 280mm (70-200 f/4 USM + 1.4x extender) so maybe beggars shouldn't be choosers?

I'd have to figure the Tamron would clean up over that combination's image quality like the 400 prime does.

I'll consider buying the lens if:

-- Image quality at 400mm and beyond is reasonable for the price. I'm not expecting Canon prime 400mm f/5.6 performance at 400mm, but I would like this lens at ~ 560mm (double pixels on subject) to be better than the 400mm f/5.6.
-- Autofocus is at least decent speed, given the ultrasonic motor I think this is likely to be ok. Again, I don't expect miracles here. If it can focus as well as the 70-200 with an extender I'd be ok. 55-250 focusing speed would not be acceptable to me.
-- I decide the weight is in the range I'm willing to carry, it's over 1.5 lbs heavier than 400mm f/5.6!

Dave