What is the best focal length for bird photography?
While 300mm, 400mm, and even short zoom lenses can be useful at times for
bird photography, my recommendation to those seriously interested in making
quality photographs of birds is to purchase a lens with a focal length of
at least 500mm. For photographing birds in flight, however,
handheld 400mm f/5.6 lenses perform superbly.
And in places like South Florida where the birds are
extraordinarily tame, a 400mm lens may suffice as an everyday bird lens.
Image size is, however, a function of the square of the focal length,
so a minimum focal length of 500mm is preferable.
With the addition of the matched 1.4X teleconverter,
you'll have an effective focal length of 700mm.
You'll have many more chances to photograph birds than you would
with any shorter telephoto lens.
At present, the premier bird photography lenses are the
600mm f/4 autofocus lenses; my Canon EF 600mm f/4.0 L lens --
often with the EF 1.4X teleconverter in place -- is my everyday,
workhorse bird photography lens. These big guns are, however,
extremely expensive and brutally heavy--the lenses alone weigh
almost 14 pounds. Before you run out and buy a 600 f/4 lens,
rent or borrow one and see if you can manage it in the field.
Remember, you may be walking miles on occasion.
And remember to be careful and not to drop the big lens!
Manual focus 800mm lenses can be purchased for well
less than either the 500mm or 600 autofocus lenses,
and provide a reasonable option for serious bird photographers.
Their minimum focusing distances are in the 30-45 foot range;
extension tubes need to be added and removed constantly when
working with avian subjects at close range.
(The 600mm autofocus lenses feature minimum focusing distances of
less than 20 feet, even when used with a 1.4X teleconverter
at 840mm effective focal length.)
Let me repeat, however, 600mm autofocus lenses are brutally heavy!