I think if I was so motivated I could drive myself nuttier than I already am trying to figure out the absolute best combination of "speed" (meaning max aperture), focal length and sharpness for every situation but, luckily, I'm not. Photography is *always* a bit of juggling routine but the 18-105mm is fast enough and flexible enough and sharp enough that moving away from this lens requires an argument: What do I need that this lens is not providing me?
Sharpness? Okay... My 85mm f/1.8G has that covered, so if that's the over-riding concern I switch to it... Focal length? Okay... My Tokina 11-16mm can go wider and 55-200mm can go longer... You get the idea and this same thing would hold true for the 18-140mm, probably just more so. But at some point in my opinion, and really my whole point here is that we, as photographers, at some point need stop asking, "What lens do I need to get the shot I want?" and *start* asking, "How do I get the shot I want with the lens I have?" One path leads to lens acquisition and little more, the other leads to better photography. And I say this as lover of the prime lens. LOVES me a good prime, make no mistake. But even so, the 18-105 or the 18-140mm, would be the lens I would probably grab if I could have but one. Probably... That's a decision I hope I would never have to *actually* make.
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