helpful how is it that you can use 3-4 times faster shutter speed with an 85mm 1.8 -vs- a 70-200mm 2.8 IS? you can react faster with a prime than a zoom? halos around out of focus objects making things appear less sharp?
dude, what are you talking about?
I will answer, but by my answer I mean no disrespect to those, like myself, who invested over $2,000 in the 70-200 lens:
In regards to stops:
The transmission of the 70-200 II is T/3.4. The Tstop of the 85mm f/1.8, in both Nikon AF-D and Canon USM versions, is almost exactly T/1.8 as advertised. Let's just say 1.9 to be safe. The reason for the difference is because of the sophisticated lens design in the 70-200mm II that is used to correct aberrations at many distances and many focal lengths, not to mention the extra elements used for the IS unit.
To compute the relative speed of lenses to one another, one simply divides the higher Tstop value by the lower Tstop value, then squares the result.
3.4/1.9 = 1.789
1.789 squared = 3.2, i.e., three times faster of a shutter speed. 3-4 times was a bit of an exaggeration because I did not actually do the math, but was just basing it off of real-world experience.
In regards to out of focus characteristics:
There are those who look at the edge of someone's jersey, and see a halo/blur, and return their lenses, not realizing that the plane of focus is sharp. It happens most often when people are shooting stage events from down in the seating, and their cameras consistently focus around waist level because that's the nearest object within the active focus points, making 80-90% of the shots unsharp.
By no means is the 85mm lens perfect, and yes, it does have the purple fringing problem, but at f/2.8 it does not have it more so than the 70-200 II lens.