I am considering getting a portrait lens - maybe the Nikon 85mm or 105mm - for my D5100 mostly to get headshots (portrait mode) with as creamy a background as possible.
I saw the CiC tutorial on DOF and it appears to suggest that the focal length has no affect on blurry backgrounds other than the fact that in wide lenses, the sharpness is skewed to the rear and blurriness is exaggerated in longer lenses because of magnification. On the face of it, there is no appreciable difference when comparing 85 and 105.
So to my question, assuming that there exists a f/1.8 105mm Nikon and I compare that with a f/1.8 85mm Nikon, would there be any consideration for blurry background keeping aside all other differences like quality of resolution, price, etc (and that I would have to increase distance with the 105 to get the same composition) - using max aperture and fixed distance when comparing.
I am confused with the following in the tutorial - not sure what is meant by "pictures will show something entirely different" - appears to contradict what was said before in the tutorial:
On the other hand, when standing in the same place and focusing on a subject at the same distance, a longer focal length lens will have a shallower depth of field (even though the pictures will show something entirely different). This is more representative of everyday use, but is an effect due to higher magnification, not focal length.