To review; a prime lens is a fixed-focal-length lens, while a zoom lens has a variable focal length. Photographers are fond of saying they have to “let their feet do the walking,” with a prime lens.
So why use one? While a prime lens of a given focal length is less versatile than a zoom whose range includes that focal length, it offers superior optical quality, wider maximum apertures (smaller f-numbers), lighter weight, smaller size and lower cost.
I think the biggest advantage to primes for an animal photographer is the larger maximum apertures (smaller f-numbers) you have available as opposed to zoom lenses. This allows photography in lower light with a shallower depth of field.
But the primes didn’t cut it on my recent trip to Yellowstone. I needed to be able to zoom in to capture the animals up close and personal. See my blog on the wildlife at Yellowstone from March 14, 2015. Then take a look at these people photos which offer a good illustration of the difference in the focal length of my zoom lens. Remember that while I took all of these images with a zoom lens set at different focal lengths, I could have used three fixed focal length lenses (prime lenses) to get the same results and in terms of sharpness, these images would have been a bit better with a prime.
All of these images were taken with a Canon EOS 6o D at 1/125 sec at f/14. Only the focal length was changed.
There are a few big advantages with a zoom. You don’t have to lug fifty million tons of equipment with you. (Keep it simple.) You have a much better chance to capture the action you are trying for if you aren’t worried about switching lenses. (Keep it simple.) And perhaps most importantly, you are having fun and creating in the moment instead of worrying about which lens to attach. You are able to relax and go with what you’ve got. Taking lenses on and off the camera slows the whole process down and can result in capturing nothing memorable at all.
Try taking some test shots at different focal lengths to get a feel for what your zoom can do so you’ll be ready for your next big photo op.