<p>Hey Ray, I have that lens and I, too, debated about whether or not to get the f/2.8 version.</p>
<p>I finally went with the f/4 for several reasons: 1) I don't do a lot of low light, hand-held photography--if it is low light, it's probably pre-dawn or sunrise on a landscape and I'm on the tripod, 2) I haul my stuff up mountains, so the size and weight was a huge factor (my D800 body and other lenses are heavy enough), 3) the quality was reputed to be good, 4) cost.</p>
<p>All-in-all, I am quite happy with my decision--image quality has been excellent. I have a buddy who shoots Canon and I see him carrying around his 70-200 f/2.8 and I am always glad I don't have to schlepp that size of a brick around.</p>
<p>BTW, I don't really think the f/4 needs a tripod collar. I have never used one and it sits just fine on my D800 on a Gitzo Mountaineer tripod/Arca Swiss ball head. Maybe someone else who has used one can chime in here.</p>
<p>As for using the lens while traveling in urban areas and for street photography, my personal opinion is that it is too big. I am moving away from using DSLRs in the city at all (except maybe for static subjects, architecture, etc.). I have a Fuji X100s I like a lot and my wife uses a Sony RX100M2 she loves. I am now thinking the iPhone6 will be my street machine--especially for candids when you can't use a normal camera without tipping off your subject.</p>
<p>Anyway, just my 2 cents--your needs will surely be different. Good luck! </p>
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