I have a Nikon D5100 and would like a standard 50mm lens.
Considering the Nikon 1.5 crop factor, Is the Nikkor 35mm DX as close to a effective 50mm as I can get with this camera?
If you mean: Is 35mm on my DX camera the same as 50mm on Full Frame? Than it almost is. I think that also nikon presents it as prime lens for DX cameras which should be equivalent to 50mm on FX.
But if you want to get 50mm on DX, than you have to buy 50 mm lens :) It would be like 75 mm on FX.
BTW: I have this lens (35mm f1.8) and it's great choice for the price :)
Given the crop factor of 1.5x for the DX format/APS-C size sensor of the D5100, the 35mm 1.8 lens will have a full frame/35mm equivalent of 52.5mm.
35mm x crop (1.5x) = 52.5
If your question is "is the 35mm lense the same as a 50mm lens on a full fram camera" then the answer is yes but only in terms of focal length.
Further reading: http://www.kenrockwell.com/tech/crop-factor.htm
If a prime lens is not a requirement, I'm sure you can get much closer. Set a zoom to 33.34mm and it'll be almost perfectly 50mm (50.01mm).
A 50mm lens is typically not 50mm, however. Search out a patent and you'll find things like this which point to a new 50mm f1.2, which is actually 51.63mm. So in other words, getting an absolutely perfect 50mm-equivalent is sort of pointless -- close is good enough.
The "normal" lens focal length is (most of the time, excluding "weird" formats) the diagonal of the sensor, the D5100 sensor size is 23.6 x 15.7 mm (according to dcreview) so the diagonal is 32.62mm.
The closest lens is 35mm, but it is only slightly closer than 30mm (Sigma makes a 30mm for Nikon).
Both the 30mm and 35mm are good "normal lens" choices for an APS-C camera
If you mean the labeled focal length, No, after a quick search I find that you can get a 50mm lens for the D5100. If you mean 35mm equivalent then probably yes, unless you use a zoom lens.
Doing a little bit of maths and research, I came up with:
1.5 * 35 = 52.5
This comes from the crop factor of the camera multiplied by the focal length of the lens.