Hi Koen,
In short, I would suggest to go for the 50mm 1.8 AND an inexpensive
third-party flash (Cobra, Sunpak or Metz) if you feel a need for both.
Both should be about the same price or even cheaper than the 50mm 1.4.
I would only consider the 1.4 if you have a frequent need for that extra
stop. Yes, the lens is a bit better built, but it shows more distortion
and has a less flat field, meaning it is less adequate for copy or macro
(the 50 1.8 can be used with success for such applications, with an
extension tube). And it is also much more expensive.
I'm not aware of a specific coating for the 50mm 1.8. It should be the
same as for other AF lenses. More elements/groups is not by definition
better. Usually, additional lenses/elements are used to correct optical
aberrations. But more lenses does not mean better: more lenses may be
used when the lens is more difficult to correct (macro lens, fast lens,
zoom,...). More lenses also tend to decrease the contrast (each
air/glass surface reflects a portion of light).
As a side note, I noticed you have have both hoods and UV filters for
your lenses. If you use your lens hoods (which is a very good practice),
you do not need UV filters in normal conditions. Feel free to keep it if
you feel better with that extra protection, but know that it won't help
in image quality.
Hope this helps,
Nicolas.
