I had this lens for a while, but i sold it. I own the 100-400 IS USM, and i wanted a lens which will give me more detail. i have a 50D body, and i photograph birds and wildlife. The truth is i didn't see difference between the 300 and the 100-400, quality speaking (at least obvious), and because the 300 is not enough for me (it's lenght), i decided to sell it.


But, it's handling and the feeling is much better for me than the 100-400, and also i liked the attached hood it had...My opinion is a good lense, about as sharp as the 100-400, but not like the 400 f/5,6. it has the advantage of close focusing, light, fast focusing, very nice feeling in the hand etc, but it had the disadvantage of being too short for my needs. if this is not a problem for you, i think is a good choise.


You can also consider the 100-400 (it's benefit is the zoom range and i found it in same quality as the 300)
<h6>the 5,6 which has the same feeling with the 300 and is sharper (but no IS).</h6>


as far as i know, these lenses are about the same price range, and the same category in quality. For me for example, which i use now the 400/5,6 and also the 100-400, my next lense is going to be the Canon's 500 f/4. you get in an other level with those expensive lenses..