Skill Level Intermediate
- I've been a photographer for what sometimes feels like forever, and yet I'm still amazed sometimes at all of the decisions that I have to make, especially when it comes to equipment. Even a task as simple as choosing a lens, sometimes it seems there are so many variables involved. Here, for example, I have a couple of lenses that have the exact same focal length range. These are both 24-70mm lenses, so they're giving me the same field of view. But there is an important difference, and that would be the maximum aperture size.
This smaller lens is only able to open up to a maximum aperture size of f/4, whereas the larger lens is able to open up even further, all the way to f/2.8. So when we have lenses that for all intents and purposes are essentially identical except for that difference in the maximum aperture size, how do you make a decision? Well, there are a few factors involved. First off, you can see there's an obvious size difference. There are more lens elements required in order to accommodate that larger aperture size, and so the lens itself is going to be larger.
It's also going to be a little bit heavier. That lens that has more lens elements, in this case the f/2.8 versus the f/4, is going to be larger and heavier. So, do we really need f/2.8 then? Well, we're also talking about in a more expensive price point. The f/2.8 version of a lens will be more expensive than a comparable f/4 version of a lens, for example. So far, it's seeming like f/4 might be the way to go, but do you need to be able to open up that aperture even further than the f/4, for example? And obviously in this case, I'm talking about a particular pair of lenses, one that goes to f/4, one that goes to f/2.8.
That is a somewhat common pairing in terms of maximum aperture sizes. But there will be differences with different lenses of different focal lengths. But there are two factors that you'll definitely want to consider if you're trying to decide between lenses like this, where we could go to a larger aperture size. One of those, may be more obvious of the two factors, would be depth of field. With a lens that's able to open up that aperture to a larger size, we're able to get narrower depth of field. So if you like to try to minimize depth of field in certain situations photographically, you may very well want a lens that can open up with a wider aperture and therefore, that can give you more narrow depth of field.
But there's another factor that I think a lot of photographers don't tend to think about, and that is auto-focus performance. When we're configuring our camera, when we're tracking a subject and focusing, auto-focusing on that subject, the lens itself has the aperture wide open. Well, with an f/2.8 lens as compared to an f/4 lens, that means that when we're wide open, we're letting in a lot more light, and that can improve auto-focus performance. So, if you're photographing moving subjects, maybe sports or birds, fast-moving subjects where you really need the best auto-focus performance, or if you're shooting in low-light situations where you need good auto-focus performance, it may very well be worthwhile to get that lens that can open up to a larger lens aperture.
So, there are factors to consider overall. The size, the weight, the price. But be sure to think about the overall possibilities in terms of depth of field, as well as the potential improvements in terms of auto-focus performance when you're choosing between similar lenses with different maximum aperture sizes.