I also think that there is a degradation that comes with thee things and the companies that are making fast primes are generally going for the best MTF curve they can get. So putting the IS gizmo in there costs them some performance in that regard. Zooms are always a compromise so for those it doesn't matter as much (and they are already big and heavy).I'm wondering why fast primes like a 35/1.4 or a 85/1.2 don't come with IS. The fastest lens to feature IS is the 35mm (and the 200mm) f2. Why is that? People would love a 50mm f1.2 IS Is there some sort of technical problem? I can't imagine anything else, it would sell well, would set them apart, isn't too expensive... Can someone help me?Hi tayassu!
I will try to make an approach, as far as I can handle your question:
IS (Canon) is a moving optical element inside the lens.
To work properly it has to move fast and accurate. To be fast it has to be of low weight.
Fast apertures need a larger image circle over the whole optics compared to narrow apertures.
Therefore the optical elements of the IS should be larger as well. This leads to higher weight which causes loss of speed and higher energy consumption and also to higher prices because of the more expensive optics.
So with IS Canon always compromises between functionality of the IS and useful max. aperture.
This is my conclusion. Maybe someone else can do better.