Aaron Lewis Photography wrote:

ImageX wrote:
Well I guess that's what I'm asking. What are we giving up, other than the 1 stop to save $1000

So we're assuming that from f4 to f5.6 will be less than tack sharp because it's near the limits of the lens?

It really depends on what you are going to shoot with it and what camera you will be using. If you are using a D800 and shoot landscapes or just demand a tack sharp image edge to edge I think the F4 to be the choice.
So far it seems to be a very nice lens.
From what I am reading it is a better lens at the short end than the 2.8...No surprise there.
The stop difference isn't as critical as it was just a few years ago...For the most part you can just bump your ISO.

In the studio the f4 will be great (technically better), but in the field the 2.8 could be a background saver. The f4 out of focus area will not match the gorgeous bokeh of the 2.8. For portrait work I think the 2.8 is about as good as it gets, but (to be fair to the f4) your style of portraiture will come in to play here....If you shoot lots of wide DOF portraits the f4 could suite you better....

If you are a wedding shooter 2.8 hands down.
If you often shoot in low light the 2.8 will provide faster focus... If you are shooting under pressure this will translate into more sharp keepers.
If you are a sports shooter 2.8....No question.

Hope that helps bro!
Peace