adamo99 wrote in post #16384769
What exactly is going to improve if the same lens is mounted on a full frame body??
To be fair, buying a pricey lens like this and not using it on a FF camera is sort of wasteful. You are paying for the extra glass and all that's designed and built to produce an image circle large enough to cover a 24x36mm sensor, but actually using less than 40% of that area with approx. a 15x22mm sensor.
1. Using only the central part of many lenses can be an advantage... You end up using their "best parts" or the central sweet spot of a lens that's typically sharper and less prone to various types of optical faults than the corners.
2. Some don't like the focal length range of 24-70 on a crop camera, while others love it. Personally I find it very useful. In fact I like a 24-70 better as a portrait lens on a crop camera than on a FF camera. But, sure... a 24mm lens isn't at all wide on a crop camera. So for general walk-around purpose, I pair it up with a Canon 10-22mm or Tokina 12-24mm, which gives me a neat, two lens kit (to be honest I rarely carry only those two... usually I also have at least a 70-200 or 135mm, and often have a 300mm with a 1.4X teleconverter, too).
As to quality... well a crop camera is in some respects more demanding on lenses than a FF camera. While it's true in most cases that the cropper primarily uses the best part of the lens, that's good because the 18 and 20MP croppers have more than twice the pixel sites per square mm than the 21 and 22MP FF cameras, essentially asking the lens to resolve the image more clearly. So a premium quality lens from the Canon L-series line might be an ideal choice, so long as the price tag isn't too much of a shock.
All EF lenses are usable on all EOS cameras. On the other hand, ED-S lenses are only usable on APS-C/1.6X crop bodies (from 300D or original Digital Rebel onward). So most crop cameras can use both types of lenses freely. It's full frame cameras that are somewhat limited to FF compatible lenses only.