Which lense will give me the best depth of field?
These are the 3 i'm considering:
http://www.nikonusa.com/...s-Overview
http://www.nikonusa.com/...s-Overview
http://www.nikonusa.com/.../1.8G.html
I have the nikon d5100 and i'm looking for the best lense that will have the most shallow depth of field and be best for professional looking portraits?
Best depth of field?
Do you mean the deepest depth of field? The wider angle the lens, the more apparent depth of field. (10-24 mm will produce good depth of field)
Do you mean a lens that provides the best selective depth of field? The longer the lens the shallower the depth of field
Any of the AF-S lenses with apertures of f/1.8 or f/1.8 will do the trick for shallow depth of field.
The 50mm f1.4 will give you the shallowest depth of field of those choices. The larger the aperture, the shallower the DOF.
The one with the most shallow DOF is the first one, the 1.8, The one with the greatest range in DOF is the second, because it gives you an extra stop on the closed end and you only lose 1/2 a shop on the open end. The last one has the least DOF, since it goes from 1.8 to 16, where the first goes from 1.4 to 16 and the second from 1.8 to 22.
For practical purposes, you are probably not going to see a huge difference between the 1.4 and 1.8. The first and third give you a silent wave motor, so if that is of importance, it would be worth getting. Of the three, I would probably save some money, get the 3rd with the silent wave motor.
Basically what the others said, but I would just like to point out that the 50mm f/1.8D doesn't have a focus motor in it, so with your D5100 it will NOT autofocus.
If you want the shallowest depth of field, go with the 1.4 (i.e., the first lens on your list).It'll be quite a bit more pricey though.
First, only the AF-S models will auto focus on your D5100.
Second, any 50mm lens at f1.8 on your D5100 will give you the same identical depth of field at the same subject distance. Remember, there are only three factors that affect your depth of field:
1) The focal length of the lens.
2) The aperture used.
3) Subject distance.
This should help you to better understand depth of field:
http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml