I'd been considering a large telephoto zoom lens for months now, not just for birds, but for other subjects as well. The 1.4x extender on the 70-200 worked well enough but at the cost of some quality and I wasn't that happy with the results, as using the bare lens then doing a hefty crop often produced more pleasing results. Many times since December I have perused magazine pages and websites looking at Canon and Sigma long zooms and comparing them. In the end the choice came down to the Canon 100-400 L IS or the Sigma 120-400mm OS which is half the Canon's price.
Anyway, and this is where the weakness comes in, I'd resisted getting a large zoom for ages but finally weakened before completely caving in yesterday and bought a Canon 100-400mm L lens. Unfortunately the weather is still crap - crappier in fact - being foggy and grey all day and the birds have vanished (it's that time of year), so I have not had a chance to properly try it out yet.
One of my aunt's cats, Molly, was a less-than-willing subject. (Yeah. Cats. I know. But Molly and her sister are indoor cats, from Cats Protection).
And a noisy pic of a Chinook helicopter that was flying around this afternoon. The light and visibility were atrocious
I am keeping the 400mm f/5.6 - I'd solicited opinions on Bird Forum and elsewhere and it seems that a lot of people have both lenses - as I can't bear to part with it and it remains one of the best birding lenses there is.