Whenever I drive on non-Interstate Western U.S. highways I always have the longest lens that I have with me attached to a ready camera which I can grab for a wildlife shot without having to take a camera out of a bag or case or change lenses. My rationale for this is that I will normally have time to switch lenses for subjects requiring a shorter lens but will seldom have the time to switch lenses if an animal comes into view. This system has enabled me to get some nice wildlife shots which I would have otherwise missed.

I was driving in Yosemite National Park about noon today and found a lovely meadow with a pond that was backed up by the beautiful mountains surrounding the Valley. The mountains were reflected in the pond and it was a superbly photogenic sight. AND I DID HAVE TIME TO SWITCH LENSES...

I removed the 70-200mm f/4L IS lens from my 40D and replaced it with a 12-24mm f/4 Tokina. I walked out on a path into the meadow and found that the 12-24mm on my 40D and 24-70L on my 30D were the perfect focal length combination. UNTIL...

A mother black bear lead her two playful cubs out into the meadow. I don't disturb wild animals to get their picture and i certainly would not disturb a mother bear and her cubs to get close enough to use a 24-70mm lens...

By the time I hurried back to my vehicle to retrieve my tele lens; momma bear and the cubs had wandered off. If I had my usual combination of telephoto zoom and mid-range zoom out in the meadow - I would now have some neat images.