« on: February 11, 2013, 08:02:58 AM »
But there ought to be some room for a EF-S telephoto lens with the inherent advantages of weight reduction from the shortcuts the lensmakers can take when designing for a smaller image circle. I am almost certain there will be something like this coming for the M-mount, and I think a conversion to EF-S would be easy, as the glass is for the same sensor size, and the difference is in the mount and flange distance as I understand it.
Anyways, a 300mm f2.8 for EF-S, at the weight as the 300 f4 or less? They could get away with a weather sealed plastic build (something like the 17-55 2.8 ) if done properly, and the price is right. (Yes, dreaming now, but...)
Smell that? It's sweet-and-sour scent of optical physics and lens design waking you from your dream...
A telephoto lens design places the 'virtual' aperture at or near the front element. So, a 300/2.8 lens is going to need at least a ~107mm diameter front element to fill that aperture with light. That front element is going to be big and heavy, and need a strong frame to support it. A smaller image circle would mean a slight reduction in some of the internal elements, but won't really make the lens smaller (or cheaper).
There's a reason we don't see EF-S telephoto lenses (except one zoom that actually starts in the normal range and has a variable aperture, meaning a different lens design) - there's just no real advantage to a smaller image circle at long focal lengths.