Carsten,
It used to be a matter of low light shooting capability. Then ISO 1600 was too grainy. Now ISO 6400 on my Canon 5DII is pretty usable and cleans up nicely. So the "Low Light" excuse for 1.2 lust is no longer tenable in most cases. Actually, the inexpensive EF 50mm 1.4 is a well built sharp performer and could be nominated for L-ness is Canon wished.
B&H: EF 50mm f1.4 $329
10.23 oz (290 g)
The plastic bodied Canon 50mm 1.8 is a perfectly adequate lens too and no doubt would not limit most all work could demand of it. Perhaps the contrast is indeed better on the EF 1.4.
B&H: Canon 50mm f 1.2 L $1299
1.30 lb (590 g)
"A Ring-type USM (Ultrasonic motor) uses ultrasonic frequency vibrations to drive extremely rapid auto focus with near-silent operation. A high-speed CPU and improved AF algorithm contribute further to AF speed. Good holding torque stops the focusing lens group without overshoot. Full time electronic manual focus override is available without having to switch out of AF."
Yes, the 50 mm 1.2
is indeed very special in that it's bokeh is beautiful at 1.2 to 2.0 and it's pretty glare resistant. It's a great portrait lens for pulling the person out of the b.g. However, the 50 1.4 might very well be free of Chromatic Aberration at f1.4. Of course, it can be corrected, but something to know.
B&H: Canon EF 50mm f1.8 at $110
4.6 oz (130 g)
But the truth is that the humble plastic-bodied EF 50mm 1.8 could do all the work a skilled photographer would demand of it. One could shoot an entire wedding with this one lens and stitch vast panoramas or add an extension tube and do macros of insects all at $110 for EF 50mm 1.8 version II!
For those who like dreamier and shoot into the light and can carry the weight, the 50mm 1.2L is a wonderful beast to have on ones team! Frankly, if have all three and hardly every is the 2 lesser lenses! It costs more than 10X the adequate EF 1.8. The latter is always good for going lighter or as a spare for when tripods get knocked over, LOL and it happens!
Asher