The new STM contrast, has the following advantages:
+ At the long end already with "open aperture" f5.6 sharp (well !!)
+ Silently, both AF and IS
+ Significantly faster autofocus
+ No rotating front element more
+ Wertigere processing
+ Immediately MF Override possible
equal
= Strong vignette at 250mm and f5.6
= Plastic bayonet
Disadvantages: none detected.
It's just amazing mood because the sum of the individual improvements makes the new STM better by at least one class, in my opinion.
For completeness, it should be noted that at the long end with the old IS-sharp images are possible at 250mm when to fade to f8. Then the two do not take much.
