Written by: Tiffany Joyce
Lenses can be categorized in two ways: whether it’s focal length is fixed or changeable and its focal length measurement.
Fixed vs. Changeable Focal Length
Let’s say you are taking a picture of a group. How you take their picture is totally dependent on what type of lens your camera has. Prime lenses have a fixed focal length which means that you cannot change your field of view. If you want to to fill the frame with your friends then you have to physically move closer to them. The zoom lenses‘ focal length, on the other hand, can be changed. You can just stay put and zoom into your subject.
Fixed vs. Changeable Focal Length
Focal Length Measurements
Lenses can also be categorized as either wide angle, standard or telephoto with regards to their focal length measurement in millimeters.
Wide Angle Lens
Any lens less than 28mm is considered a wide angle lens. These types of lenses are popular with landscape photographers since it allows them to take pictures that show more of the scene.
These are the bigger lenses whose focal length is more than 80mm. These lenses are usually used by wild life and sports photographers, whose works do not allow them to get physically close to their subject.
All the three categories above can either be a prime or a zoom lens. For example, a lens that is fixed at 50mm is called a standard prime lens, a lens that is marked as 80-200mm is called a telephoto zoom since you are able to change the focal length between 80 to 200mm.
Another factor to consider when looking at lenses is the aperture. The aperture is basically just the opening that allows light to hit you camera’s sensor which, in turn, creates the image. You can compare the aperture to the iris in your eyes. The more open it is, the more light gets in. Now you will not see any aperture value on your lens or camera but instead you will see something called a f-stop. All you need to understand as you begin learning about photography is that the lower the f-stop, the bigger the aperture opening. You can use the picture below to see the relationship between the two.
If you set your aperture at f/2, your camera will be able to capture the image faster than it would if it was at f/8 since more light hits your sensor at f/2. If you want to learn more details about apertures and f-stops then you can go here.
The maximum aperture opening or lowest f-stop is clearly marked on camera lenses. It is the number found after the mark “1:”. The reason for this is that not all lenses have the same maximum aperture but all can go to at least f/22 on the other end. Some lenses can only go up to f/3.5 while some can go to f/1.8. The lower the maximum aperture, the faster the lens is (again because it can open wider to let in more light).
It’s an ongoing joke that the maximum aperture is stated on the lens because, the lower the f-stop, the more expensive the lens is. On some zoom lenses, you can see two maximum aperture numbers. Let’s take the Canon lens 18-55mm 1:3.5-5.6. This means that the maximum aperture depends on what you set your focal length to. The first number, in this case 3.5, is the maximum aperture setting at the wide-angle side of the lens i.e. 18mm. The second number, 5.6, is the maximum at it’s telephoto side i.e. 55mm. The difference due to the movement of the lenses when you’re actually zooming in or out.
Depth of Field
What’s useful about understanding even just a little bit about f-stops is that it controls how much of your picture is in focus or the depth of field. For the picture below, an f-stop of f/11 was selected and the light green pencil in the middle was the point of focus. You can see that all the pencils in frame are in focus. This is what is called a deep depth of field.
For the next picture, an f-stop of f/1.8 was selected and the light green pencil was again the point of focus. What you’ll notice is that the farther you move away from the point of focus, the less sharp the image becomes. This is called a shallow depth of field.
The lower the f-stop, the more shallow your depth of field is and vice versa. So if you want to take a landscape picture with everything in focus, you will need to select a high f-stop like f/16. If you want to focus on one specific object and throw everything else out of focus then select a low f-stop.
- Using the picture on the left, you can tell that it is a zoom lens since you can change the focal length between 24-120mm.
- Since the focal length 24-120mm mainly falls within the standard range, this is considered a standard zoom lens.
- The maximum aperture of the lens if it’s at 24mm us 3.5.
-The maximum aperture of the lens when it’s at 120mm is 5.6.
For more on lenses, read this.
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