It Depends on Whether You're Shooting Postage Stamps or Poisonous Snakes
When getting into close-up photography, one is confronted with a choice of focal lengths ranging from around 55mm up to around 200mm. But these things are expensive, and with most purporting to focus to 1:1, or what is known as "life size," what's your best option? Choose wisely.
Let's look at Nikon's family of macro lenses (or what they call "micro lenses" for some reason). Even if you prefer third-party lenses, those made by Nikon can still serve as a good baseline for what the market offers. Lenses from Tamron, Tokina, Sigma and others are created to compete with Nikon's. There are differences, but within each manufacturer' offerings, macro lenses tend to come in what could be termed "short," "medium," and "long" focal lengths. With Nikon, these categories are represented by 60mm, 105mm, and 200mm focal lengths. In other words, each successive one roughly doubles the focal length of its shorter length sibling. Beyond this basic metric of course, all of Nikon's macro lenses share a lot in common. As with all macro lenses, they let you get a lot closer than you can with an equivalent regular (non-macro) lens. They achieve this by featuring longer focusing helicoids, letting you continue to focus closer when other lenses reach the end of their range. Stick an extension tube behind a regular lens to let you focus equally close and you've turned that regular lens into an impromptu macro lens.
In the case of Nikon's macro lenses, all three focal lengths let you get all the way up to 1:1, the magnification where the representation of a subject as captured is the same size as that object is in real life. Photograph a coin that is 1.5 inches across such that it fills the frame width on a full-frame DSLR, and you will be looking at it in "life size." But then if you have a choice of focal lengths, all of which get you as close as life size, which focal length is best?
To answer that question, let's look more deeply at how focal length affects things.
Seeming to correlate well with focal length, the most obvious difference between macro lenses is their cost. All things being equal, longer focal length macro lenses tend to cost more than shorter ones. But while nobody wants to spend more than they have to, I wouldn't recommend investing in a lens just because it's cheaper than others either. Buying solely based on budget doesn't seem like a very good strategy where quality is important. And I'm guessing it does with most of you reading here. So, what else?
Weight tracks fairly closely with focal length too. More glass costs more. That makes sense. Telephoto lenses tend to weigh more and cost more than more modest focal lengths when shopping for all types of lenses, so why should macro lenses be any different? With most lenses though, it's more obvious what you are buying for your money. Longer focal length lenses seemingly magnify more by taking in a narrower angle of view than do wide angle ones. Focal length doesn't directly change perspective though. Longer lenses don't really compress perspective any more than wider angle lenses distort it. If you were to shoot both from the same distance and then crop the results to an equivalent framing, your results would be identical (neglecting the obvious difference in loss of resolution from cropping of course).
But this is the point, we don't shoot both from the same distance. We shoot telephoto subjects from a distance, and we shoot wide angles from up close and personal. Shoot a wide-angle lens from a far away and that subject will be tiny in the frame. Clearly, each end of the focal length scale lends itself to a particular shooting distance.
Macro lenses are no different in this regard. If you shoot with a 60mm macro lens and a 200mm macro from the same distance, the wider lens will take in more angle of view, making everything in the frame look smaller. That is to say, if you want to reach 1:1 with that 60mm macro you're going to have to get a lot closer than with that 200mm. Both can reach full life size, but to do so you'll have to get closer with the wider lens.
Just how far away you can be and still reach 1:1 is known as "working distance." Longer focal length macro lenses afford you greater working distance than shorter ones do. And when considering your optimal working distance, I always say it depends on whether you are shooting postage stamps or poisonous snakes. Both subjects can be accepted as valid and potentially interesting close-up for close-up work, depending on your tastes and other hobbies presumably. If your favorite subject might possibly strike out and bite you, you're going to want to keep your distance. I'm not a snake person, but maintaining a safe working distance is likely one of the first things you would learn if this is your thing. If instead your subject will politely lie there in your stamp album, you can afford to get a bit closer. The Nikon 60mm macro has a closest focus distance of around eight inches. The 200mm Micro-NIKKOR will keep you at least a foot and a half away. Take your pick, but choose wisely.
The same is true with background coverage. With its wide angle of view, the 60mm Micro-NIKKOR can see around 40 degrees when measured on the diagonal. Being more on the telephoto end of the scale, the 200mm Micro-NIKKOR takes in only about 12 degrees. By providing a narrower angle of view, the longer macro lets you more easily isolate your subject. With its wider view, you will see more extraneous detail behind your subject when shooting with the wider macro. If you're shooting postage stamps or other flat subjects where the background can be easily controlled if not cropped out entirely, a 60mm macro will work nicely and will save you both money and weight. But if you're shooting a poisonous snake (or really any arbitrarily shaped three-dimensional subject), you're going to appreciate the longer 200mm Micro-NIKKOR. Or whatever your favorite brand's equivalent of this would be, of course.
So, in terms of magnification power, all macro lenses that let you reach 1:1 life size are good options. But focal length does have a significant impact in terms of working distance and background coverage. What your best option is depends on what you expect to be shooting.
Choose wisely to avoid getting bit.