I often get asked by people “If I can only get one lens, which one should I buy?”. There are a huge amount of factors which could go into a question like that. The answer is different for everyone and really comes down to what you need the lens for. But I thought I would spend a few minutes and give an overview of focal lengths and how they affect your photos. There are a lot of other features and differences in lenses, but we’ll save those for another time.
Lenses come in many different shapes and sizes. But if you’ve ever seen one, you probably noticed that they are referred to by using a number followed by “mm”. The “mm” refers to the focal length of the lens. Lenses with a single number such as “50mm” are prime lenses and you can’t change their focal length. Lenses with a range such as 24-70 or 70-200 are zoom lenses and their focal length can be adjusted to the range between the two numbers.
A standard 50mm lens on a full frame camera has about the same focal length as the human eye. In other words, if you look through a camera with a 50mm prime lens on it you will have about the same range of vision as you would if you closed one eye and looked at the same thing. Lenses that are referred to as “wide angle” give you a wider perspective than your eye, and ones referred to as “telephoto” bring things closer than your eye.
But how does this all affect your photo? In simple terms you can just remember this. Wide angle lenses push things apart and give you a broader perspective. Telephoto lenses pull things together and give you a tighter perspective. Below are a few examples.
The below image on the left was taken with a 15mm lens. You can see it’s a very broad perspective and pushes all the trees apart. The one on the right was taken with a 200mm lens and you can see it pulls the trees in close to the subject and gives you a very tight perspective. As you create images you need to decide which view of the subject you want to show.
Just to give some perspective, in the diagram below you can see where I was standing for each image.
In this example, the left photo was also taken with a 15mm lens and the right photo with a 24mm lens. You can see how when the frame is filled with the people in the first image the building is much smaller than in the second image. The wider lens pushes the building away, where the 24mm one pulls it in. Had I shot this same image with a 200mm lens the building would be huge in the background.
In the below diagram you can see I moved a few feet back for the 24mm lens, but it actually pulled the building closer to my subjects. The interesting thing to note is that neither the people nor the building moved. It looks like they are closer to the building in the second photo just because of the perspective of the lens.
In this example, I stood in one place with a 70-200 lens. The first one was taken at 70mm and you can see the buildings are way off in the background. The second was taken at 140mm and you can see it pulled the subjects closer to the camera as well as the buildings closer to the subject. The third was taken at 200mm and the subjects are even closer to the camera and buildings even closer to the subject.
So in the end as you choose which lenses to buy, it’s a good idea to decide the maximum range you will need and for what purpose you will be using the lens. In other words a 400mm lens would be ideal for bird watching, but a very bad choice if you like to do lots of group photos in a small spaces. A good choice for a basic work horse lens would be anything that has a range wide angle to telephoto (e.g. 24-70, or 28-80 etc.)