A few years back I bought the best X-300mm I could afford. The Sigma 70-300 DG Macro. After a while I found it to be too dark and upgraded to the canon, which is ultrasonic and doesn't scare the deer (a nice extra).
I've since then moved away from the Canadian Rockies and, therefore, don't have much wildlife left to shoot. Over the years I picked up the Canon 100mm 2.8 macro and the 50mm 1.8. Both are wonderful lenses and very sharp.
FF to a couple weeks ago when I was in Brasil trying to shoot some birds. I found my good old (cheap) 70-300 to be so soft and slow! It took me a while to realize that I'd gotten used to my wonderful (fast) primes.
Am I the only one to have gone through that? I'd hate to imagine what'll happen once I buy my first L glass !! (cue fade into a lens-laden dreamland)
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KT