Just so I am not leading anyone on, I am not going to list the 10 best lenses for nature photography or anything like that. I don't think there is such a thing. Lenses are best for specific purposes and how and what you photograph will influence what you need for a set of lenses.
So I am going to talk a bit about the lenses I most commonly use and give a story about my latest purchase. I am a big believer in buying lenses based on what you find you cannot do well with your existing gear, in other words, based on what you need.
So first, the most common lenses I use and why they fit my needs. I love the perspective of very wide-angle lenses on everything from landscapes to close-ups, so a real workhorse for me is the Canon 10-22mm EF-S lens. That focal length range fits me well. I tend to shoot mostly in the 10-15mm range because I find the perspective more interesting. I am shooting with APS-C cameras, so this lens is perfect for them. For a full-frame camera, this would be a lens with a focal length of approximately 16-35. I also like that I can get very close to a subject with this lens, down to about 10 inches, which gives some very cool effects. This next shot is with this lens at 10mm, a close-up and wide landscape.
I then skip up to two lenses I use occasionally, though they don't always travel with me, a Canon 50mm f/2.5 macro and a Canon 85mm f/1.8. I use the 50mm macro when I need a moderate focal length and a fairly fast lens, and when I need to get really close to a subject with more depth of field. Shorter focal length macro lenses will give more depth of field. I use the 85mm for its wonderful, fast max aperture of f/1.8. I love the look you get with such a lens, especially when photographing people. There are very few zoom lenses you can buy that will give you the look of an f/1.8 85mm lens.
I don't always carry those two lenses because I don't always like those focal lengths and I am not one to carry more than I have to. I find I shoot a lot of my images with the wide-angle and with a long telephoto because of the look I get. I like the perspective and depth of field that you get with both, and both give a much stronger look than middle focal lengths. That is not always a good thing, though, and sometimes I get caught not having a mid-range focal length when that is most appropriate. But I would rather travel light and sometimes get caught than carry lenses with me that I don't use very often. I will pack these lenses when I am shooting in conditions that I will likely need them.
Next, I often shoot close-ups and macro with a Sigma 180mm f/3.5 lens. This is an older macro (Sigma now makes a 150mm macro that is a very nice lens -- I have used it and have found it to be excellent -- but I am happy with the 180mm I have now, though I have been tempted by the 150mm because it is smaller). This is a real workhorse for me for close work because I like the working distance of the telephoto macro and I like the look it gives both in perspective and out-of-focus background or bokeh. This focal length does have less depth of field, so you have to be careful of your focus point, but I like the look. I will often shoot it at f/4-f/11, not at really tiny f-stops, again, because I like the look. That's what was used for the digger bees photo next.
Last, I use a zoom in the 80-400mm range. I like the longer focal lengths for everything from landscapes to birds to close-ups. The photo at the beginning of this blog post is shot at 400mm for the perspective. I do not specialize in bird photography, so this is a good all around focal length that lets me shoot wildlife when that is appropriate. I used to have a Tokina 80-400mm zoom which is a fine lens, as long as you are shooting at a distance. It only focuses to nine feet and for good reason. When you add an extension tube to get it to focus closer, the image quality really dropped. For me, close shooting is really important.
So I tried a friend's Canon 100-400mm f/4.5-5.6. I liked the image quality and it would focus up close with excellent quality. This lens focuses to just under six feet without accessories and works nicely with extension tubes to focus even closer. I was not crazy about the push-pull zoom implementation on this lens. I always found it awkward, plus the focus ring is on that moving lens element, also awkward.
Next I had the chance to try out a Sigma 120-400mm f/4.5-5.6. I was immediately impressed with the feel of this lens on camera, and it did not have a push-pull zoom! In my informal tests based on real subjects that I actually shoot, I found it was every bit as good as the Canon 100-400mm (and it is also less expensive). What about the close-focusing ability that is so important to me? This lens focuses to five feet without accessories (good) and image quality is excellent when using extension tubes to focus even closer. Is it as good as a macro up close? No, but there are no macros at this focal length, and image quality is excellent. Plus if I stop the lens down to f/8, it is so close to the 180mm macro that I can now leave the 180mm macro at home if I want to keep my gear to a minimum. This next shot is with the Sigma near its minimum focusing distance, at 400mm, f/5.6. Depth of field is extremely narrow -- the stamens of the bush poppy are sharper than the fly.
So now I am buying a Sigma 120-400mm and it will definitely become a key part of my field gear. The point to all of this is not that you should consider buying any of these lenses or that these focal lengths will work for you. I wanted to show how lens choice is strongly affected by specific needs, in this case, my needs, so your gear needs may be different than mine. But I think the thought process of picking a lens based on needs helps.
A lot of photographers now buy lenses from mail-order locations, but having a relationship with a local camera store can be worth the extra price. Most places will let you try out the lens, including shooting some images, at the minimum in store, and often letting you go outside and set up a tripod. Some stores will even let you try the lens more extensively like I have done. Many places will also rent lenses so you can try them out before buying, too.