![Quote](images/misc/quote_icon.png)
Originally Posted by
Jon Ruyle
It's important to realize. Some people pay top dollar for the fastest lenses possible, then put them on crop bodies.
However, if you buy, say, a 50mm f/1.2 for your 50D, you should be aware that your $1500 lens is acting like an 80mm f/1.9, and that an 85 mm f/1.8 is more than $1000 cheaper and has much better IQ wide open (especially if the f/1.2 is cropped). The $1000 is almost enough to make up the difference in price between the 50D and the full frame 5DII.
Similar for the 85mm f/1.2 on crop body vs 135mm f/2 on full frame (smaller price difference I think, but probably bigger IQ difference)
Don't get me wrong- I am *not* saying one shouldn't put a fast lens on a crop body. There may be reasons to prefer the 50D / 85mm f/1.2 combination (and other fast lens crop body configurations), of course. But one should be aware.