This is a great question. I love getting into the nitty-gritty of camera lenses and I enjoy looking at the specs of each lens I come across. A long time ago, I taught myself what those specs actually mean and I’ve been rewarded with knowing what I’m talking about and looking at ever since. For a lot of people, I know it can be a challenge when attempting to figure out what a lens does. Today, I’d like to demystify a few small areas.
Okay, I’m going to try to make this as clear as possible. We already know that two factors primarily determine the focus of a camera lens. Those two things are the size of the aperture that’s inside the lens as well as the distance the camera is away from whatever it’s trying to focus on. As a matter of fact, it’s fairly easy to calculate the depth of field that a camera lens can create by simply punching a few numbers into a calculator. But realistically speaking, we all need a more personal feel when we’re dealing with our cameras and lenses when we’re on the job or in the field.
I’d like to discuss the two limitations we face while focusing our camera lenses here. I don’t know if there are more limitations, but these are the two that come to mind that we all deal with every time we shoot.
Depth-of-Field: The first limitation we deal with is called depth of field. All depth of field is is the area of a scene that’s considered sharp as you’re looking through your camera lens. Again, the two primary factors that contribute to the depth of field you’ll experience are the aperture size inside the lens as well as the distance you have your camera from the subject you’re photographing. If you’re like me, you notice a stark difference between the depth of fields when having your camera as close as possible to your subject and having it further away. If you need a deeper depth of field, you can either close down (shrink) your lens’s aperture or you can move your camera away from the subject. So this is definitely something you need to consider when photographing. The reason I call it a “limitation” is because each lens handles these things in its own way. One lens might give you a sharp area that’s much deeper than another, or vice-versa. You need to know what each lens you use is capable of before using it. If you need a deep depth of field and your current lens isn’t able to give you that, you’ll need to change lenses.
Minimum Focus Distance: The second limitation we need to concern ourselves with is called minimum focus distance. Focus distance is the distance between the lens and the subject you’re shooting. I’m sure you’ve, at one time or another, tried to focus on something that was simply too close to your camera. No matter what you did, your camera couldn’t and wouldn’t focus on the subject. As you were trying to focus, you probably didn’t realize that you were up against one of your lens’s limitations, but you were. Certain lenses can only focus on something when they are at least a specific distance away from it. Beyond that distance is fine (within reason), but any closer to it, you’ll need to switch out your lens again.
If you’re into macro photography, you have most likely already discovered this limitation of your lenses. That’s usually what brings people to macro lenses; lenses that can be physically moved a much closer distance to a subject than their non-macro counterparts can. Another remedy to a focus distance that’s not close enough is to add a magnifying filter to the end of the lens in question. Magnifying filters have the capability of bringing the end of a lens mere inches from a subject while still maintaining focus. They’re incredible and very inexpensive little devices.
How can you test out what your lens is capable of? Well that’s easy. To start off, attach your camera to a tripod that’s next to a table. Place a small object on the table and then focus on the object, setting your camera to the closest possible focusing distance and making sure your lens is all the way zoomed out. Then, bring the object as close as you can to your camera, until it’s just out of focus. This is the minimum focus distance that you’re up against. If it’s too far away, you’ll need to look into other lenses that can bring you closer.
To test out depth of field, keep your camera set up the same as I just described above. Then, set your aperture to the largest and the smallest sizes. Twist and turn the object so you can get an idea of how deep or shallow the depth of field is at a certain distance. Then, change the distance and repeat. This will give you a feel of what your camera lens can do.
I know none of what I just wrote is hard data that you can run with, but more soft ideas that I’m hopeful will give you a better feel for the photography equipment you choose to use out there in the world. If you have any questions or would like to add anything to this conversation, please do so below. Thanks!