In article <47u0c6$mai@necco.harvard.edu>, haibo@matsci2.harvard.edu says...
>Thanks the previous poster for clarification.I do want to know if 50mm
>f1.4D is also a good lens for copying prints, besides low light
>applications. Because I am also going to use it for full length
>portraits with filling flash, I do hope to be able to benefit from the
>D version.
>Like to know what else can I get from f1.4 more than f1.8 other than
>65% more light. Which one has smaller distortion? Thanks.

You already have the best lens for your purposes if you have the Nikkor
50mm f1.8 AF (or plastic-barrel AIS, or E lens - which have the same optical design) - the lens has no linear distortion and has good optical performance over its full focus and aperture range. The 50mm f1.4 is excellent, but has some barrel distortion, and some compromises in performance at closest focus, at the corners at wide apertures, and at the widest aperture (it is contrastier over the majority of the frame
about f2 or so...) - so why bother? Also, unless your backgrounds and
subject are unusually light or dark, the D feature will not help you much with fill-flash exposures (and if they are unusual, manual TTL flash compensation can be used to compensate).
Hope this helps.