
Richmond, US
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Here's what's possible.
 D100, 55-200 AFS VR @ 116mm, 1/60th, f/4.8, ISO 200 - flash, bounced off wall to camera right.
On the other hand, consider this:
 D100, 55-200 AFS VR @ 145mm, 1/20th, f/5.3, ISO 1600, hand-held with VR. This one isn't nearly as crisp, largely because Pi (the subject) moved a tad in the 1/20th of the shutter. Note ISO 1600, and also that this was shot on a D100, whose noise performance is far worse than any current model. (The D100 was discontinued in 2004, essentially "forever ago" by technology standards.)
In essentially the same conditions (plus a couple of Pi-treats), here is the 50/f1.8 AFD:
 D100, 50/f1.8 AFD, 1/125th, f/1.8, ISO 800, hand-held, no flash, no VR. First, it appears that I missed the mark on the AF target by a very small amount. That's pretty easy to do on the D100 as its AF targets are very large, and Pi in this case was a bit squirmy. (Yes, that's Pi as in the statement "Pi is an irrational number.") As a result of the AF miss - which is visible here but not easy to see on the camera LCD - the left eye isn't tack sharp, while the first just a bit above that is pretty sharp. Note also that the nose is way out of focus, and would have been even with the quarter-inch of missed focus correct. The f/1.8 aperture has rendered his bell out of focus. Compare with the bell in the 55-200 shot #1. The conventional wisdom is to shoot portraits with the widest possible aperture, for the thinnest possible depth of field. And sometimes that works, but I think that in this case, a bit more than minimum DOF is best. This was shot as a demonstration, but my preference would be to shoot at around f/4 or f/5.6 and arrange for the light to suit. There is a pretty big difference in apparent sharpness between #3 and #1. Even though #3 was shot at 1/125th, easily within the normal range for hand-holding, #1 is pretty obviously much sharper - mostly due to the fact that the flash is lighting the subject and is probably quenched after about 1/4000th in this environment. Again, note that this was shot at ISO 800, pretty high for this camera, even though we were at f/1.8. And there was a fair bit of indirect sunshine in the middle of the afternoon - the light gets a lot dimmer than this. If I were doing this for real I'd go shoot it again, but in this case Pi has headed for the hills, or at least a nice warm computer upon which to curl up...
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It's also worth pointing out some other differences here. The f/1.8 lens is often a purchase because of the bokeh - or the ability to blur the background. But compare #3, at f/1.8, with #2, which is at f/5.3, which is not the conventional idea of "lifts and separates subject from background" - but there it is, almost exactly the same background as #3. It is not rendered as clutter, and if anything #2 is probably rendered slightly "smoother" than #3, although they are both nice.
Finally, compare #2 and #1, which are from the same lens and at fairly similar apertures and focal lengths. Yet the backgrounds are quite different. #1 is due to having some interesting proportion of the light provided by the flash. The flash isn't trying to light the background, and in fact does not - which is why it's pretty dark, even though the shooting environment is identical to #2. (They were shot about a minute apart.) #2, by contrast, is exposed for the ambient light, which is roughly equal between subject and background, and in fact they are so rendered. Both are valid artistic choices.
The colors are also quite different, largely due to the relatively inaccurate auto white balance of the D100, and the fact that #1 was shot with flash. (And I was too lazy to go correct the white balance in post.) These two lenses render colors in about the same way.
I'm guessing that most readers would definitely not have guessed the 55-200 to yield the visibly sharper result, nor would many have expected the background rendering similarity between #3 and #2. _____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time! Attachment
#1, (jpg file)
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#2, (jpg file)
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#3, (jpg file)
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