Help me select a lens, please!

[thekingb]

So David, between the 4 and 2.8 IS models (not II version), would i be doing myself a disservice by purchasing the f/4 and not going ahead for the 2.8? I'd like to add in a 2x teleconveter to get back the lost reach from the Sigma. Or should I not worry as much about that and focus on cropping a sharper picture, when necessary?

Don't forget about weight. The 2.8 is significantly larger and heavier than the f/4. The IQ difference is negligible. It's all about the extra stop of light and whether you need it.

[cyoung315]

I'll almost certainly be using it outside with lots of sunlight. The Sigma has actually taken some very pleasing shots with great bokah but it never gives crisp sharp subjects, they are always just under sharp but still very nice. Thats a 5-6.3 variable aperture, does the IS f/4 Canon with a 2x teleconverteron that lens sound like a good idea or would I possibly step forward to lean backwards adding the teleconverter?