Here are some basic thoughts on lenses. Some are just personal feelings, and some are my take on the facts.
For starters, there are two numbers to define your lens (mm):
1. Focal length.
<35mm – extreme wide angle,
35mm – <50mm are wider angle,
50mm is normal perspective (for people),
+50mm – 85mm are slightly tighter lenses,
+85mm are telephoto.
2. Lens Diameter.
This is basically the size of the front glass element. The larger elements capture more light, and that usually means the lens is faster. It’s also important for screw on filters and focus control rings. For example, we have a Canon L 70-200mm f2.8 lens, with a 77mm diameter.
The issue with focusing lenses is that they usually have a minimal focusing distance. Wider lenses usually have shorter focus distances, and telephoto lenses have longer focal distances, which means you have to be further away from your subject.
Wide lenses allow you to be very close to the subject—around a foot. But, sometimes they are so wide that there is more of the environment in the shot than you might want. Also, the really wide lenses tend to bend or distort the image.
On the other hand, telephoto lenses allow you zoom in on your subject, but you also have to be a good distance away to have the subject in focus. For example, our 70-200 lens has about a 5.5 foot focus distance. So, while you can be zoomed in, you also have to back away from the subject. Therefore, as odd as it might sound, a wider lens might be better for getting a close up.
Macro lenses give you the “Bug’s Life” perspective. They allow you to focus very close to the front element of the lens. There’s a really nice 100mm macro lens that allows you to be about 3 feet from the subject. Some wide macro lenses allow you to be almost touching the subject with the lens and still have good focus.
The lens speed determines how much light a lens can bring into the sensor. This helps in low light situations, and when you to want to open up the lens and drop the depth of field (especially with wider lenses). In case you need a little explanation on how depth of field and aperture relate… think of the aperture as the pupil of your eye. In bright sunlight, your pupil is really small (f16 – f22). In the dark, your pupil is as open as it can get (f2.8 – f1.4). This is why people have a harder time seeing at night. Their pupils are wide open, and less stuff is in focus. In bright sunlight, when your pupil is really small, everything is in focus. So, why does a larger number represent a smaller open? Well, the number is actually a fraction. f1/22 is really small, while f1/2.8 is really wide. Just toss out the fraction part and go with the bottom number.
Personality of lenses, based on focal length:
<35mm – extreme wide angle
This is where you want to exaggerate the environment and make it bigger than life. I always think of this as a child’s “eyes full of wonder” view. In this perspective, people are less important than their environment.
35mm- <50mm are wider angle,
This balances the people and the environment very well together. Since naturally, we almost always focus on people first, this is where you show people and the environment as one.
50mm is normal perspective,
This is the human perspective. This is the natural way we see things, so when you want your video to feel authentic, non-effected, or off-the-cuff, then this is a good place to be.
+50mm – 85mm are slightly closer lenses,
This gives a bit more weight to the people or subject of the shot while keeping them connected to their environment. Generally, the environment will be a bit out of focus, but still recognizable. This is a great zone when you interview someone in a relevant environment (scientist in the lab, farmer in the field, teacher in the classroom, etc).
+85mm are telephoto.
The longer the lens, the more the environment is reduced. This is the great for when you want a very personal perspective, almost like you’re getting in a person’s head. It’s also great for ugly interview spaces, because it minimizes the background.
One thing to keep in mind about lenses: Zoom lenses allow for more flexibility in the field, but they have more internal glass, which reduces the light reaching the sensor, and deteriorates the image quality a little bit. They are also a good bit heavier. Prime lenses have very little glass, which means they are smaller, lighter, faster and shaper.
If you have to react quickly, don’t know much about where you are going to be, or want the flexibility to shoot quickly at various focal lengths, then go with a zoom. However, when you can, start thinking of working with primes—as the old saying goes, “zoom with your feet, not with your lens.” Force yourself to think more and shoot less.