wrote:
What are canon EF-S lenses? What is the difference between EF-S & EF lenses?
Are EF-S optimized for digital cameras, to take into account the 1.6x
conversion factor on small-framed sensors?

Yes. EF-S lenses are optimized for digital cameras. They
are mechanically set up so that they are difficult or
impossible to mount on full-frame cameras.

This is because they are specialized lenses made to cover
only the smaller sensors of the typical Canon digital
camera. They are also somewhat cheaper to produce because
the image circle is smaller.

Thus full-frame lenses (EF series) will work on a 1.6x
digital but the EF-S lenses will not work on a full-frame
camera.

----- Paul J. Gans