Quote:
Originally Posted by monosodium
1) The D90 kit lens (18-105VR) is around f/4 at 35-50mm. Going to f/1.8 is basically a little over a stop.
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You need to check your math. Aperture is not linear, and going from f/4 to f/1.8 is actually 2 1/3 stops. That means a shutter speed over 4 times as fast to keep the same exposure.
As for getting adequate DOF, that depends on the distance you're shooting at. A 35mm at f/1.8 and 8' from the subject has >1' of DOF, which is plenty as long as you can focus quickly.
Edit: The max aperture with the 18-105mm (or 16-85mm, and probably 18-200mm also) is f/4.5 @ 35mm, and f/5 @ 50mm. So the actual difference is 2 2/3 stops for the 35mm, and 3 stops for the 50mm, assuming you're comparing the f/1.8 versions.