hi people always say FASTER the better faster the better etc..

how much difference is practical terms is there btw f2.8 (and below) and f4? (more specifically, those super exp 2.8 lenses vs the also quite exp f4 ones. namely the 2 versions of 70-200mm L)

Practical terms meaning :

1. Since its brighter, HOW MUCH darker or faster are u able to achieve good AF using the 2.8 vs 4.0? Would the fact taht u have a focus assist (or even better external speedlite)

[im asssuming just just coz it allow twice the light to get in, DOES NOT MEAN u can AF twice as fast, or twice as dark rite? im sure the lower DOF of the 2.8 also affects AF... so its not a linear relationship]

Anyone have any practical values? (eg. In street lamp light, 2.8 can acheve AF 50% faster, or can af 80% of the time vs f4s 50%)

2. 2.8 allows DOUBLE the light of the 4.0 right? so basically this would mean shutter speed can be TWICE as fast as if u were to use a 4.0? (correct if im wrong)

3. Bokeh wise, are both equally good?

4. distortion wise at full wide, both as good?

Thanks!!

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