Shooting sports with even a f/4 lens can be trying on cloudy or overcast days . Nothing to do but crank the ISO up . An 5.6 lens would even make it worse .
I don't know what age you're shooting , but most of the fields i've seen for youth sports have bad lighting . Most would not support using a 2.8 lens , less alone a f/4 lens , forget about a 5.6 lens
Right now it's a 9 year old and 6 year old twins and they play mostly during the day. However as they get older there will be night games that I will have to deal with. Fall sports are challenging as well because what may be a day game at the beginning of the season becomes a twilight game by the end of the season. You are absolutely right about f/5.6 essentially being worthless for anything other than sunny day games to get the SS that I need for baseball, soccer, and football. The FL of this lens is what I really want, everything else leaves something to be desired for my needs. I have thought of some different alternatives to get that FL but the ones that fit my budget are not ideal. Such is life I guess. Maybe some long-lost uncle of mine with a 300mm f/2.8 will meet his maker and leave it to me.....his sole living relative. Yeah right!


. Since I was talking mainly for sports , I don't miss the OS/IS.
