When I was buying my 40D in 2008, I was thinking well, I'll first get into Canon system and then will grow into fullframe.
And because I am a pure hobbyist, I actually never had neither the money nor the excuse to pay big $ for FF camera and lenses.
In the end I've stuck with Tamron 17-50mm f2.8 (non-VC), Canon 85mm f1.8, Canon 10-22mm, Rokinon fisheye and Canon 55-250mm.
From these lenses only Canon 85mm f1.8 is designed for FF, all others are for APS-C only.
And still these lenses are quite large compared micro43 lenses altough the sensor size difference is not that large.
Indeed, Canon APS-C sensor diagonal is 26.7mm, while m43 is 21.6mm, so the difference is just 5.1mm!
Obviously, size optimisation wasn't a priority task for designers of the lenses I own, as again opposed to m43 system.
With the high quality mirrorless cameras like Olympus E-M5, the rumored Panasonic GH3 and more and more good lenses supporting that system, it seems to me that APS-C system is becoming an anachronism.
Really, for half the weight and close price, one can build similar or better system with m43.
I really see not much point in APS-C cameras anymore. First, they're not a good helpers for you to grow to FF. Second, there is no strong commitment to this format even by manufacturers themselves. They just have produced the most necessary line of lenses, mostly mediocre quality, which is understandably to attract
amateurs by price. In all those years no single really high quality APS-C lens, which would approach to L-glass (apart from maybe the 17-50mm f2.8 by Nikon).
Most importantly I don't see any SYSTEM in APS-C especially by Canon! If it's a system, then where is the EF-S 50-150mm f2.8, which should correspond to 70-200mm in FF?
Sigma is the only helper here, where are the primes, like EF-S 15mm, EF-S 22mm, EF-S 35mm 1.8, EF-S 50mm 1.8 etc?
The idea of APS-C was nice - to make amateurs enter into interchangeable lenses world. Now, this role is better fullfilled by m43.
APS-C format was a good dollar-machine, but I believe not anymore.
Will we see slow die-out of APS-C in near future? Or Canikon will be smart enough to trasnform in into more compact format, with less pain to EF-S and DX lens owners?
I've never seen Canon sell the Rebels as a system to move to FF. It stands alone.
However, if a person has plans to move to FF in the near future, purchase lenses that are good for both. The 17-40mm L, 24-105mm L, 70-200mmL (f/4 or f/2.
, in fact, many EF lenses are out there, both high quality, or inexpensive. However, EF-S lenses will never work on a Canon FF. Buy them if you plan to stick with APS-C. There is nothing wrong with that, it will be around for a long time.