Defining zoom lens
Zoom lens definition in photography is closely related to a focal length. The latter is a physical distance between the lens and a digital sensor or a film. The bigger it is — the closer the image will be.
We can also describe the zoom notion through the concept of angles. The average human field of view is about 180° — it’s approximately equal to a lens of 50 mm focal length in a full-frame cam.
If we zoom out — or set a shorter focal length — the frame will have a wider angle and will embrace more details, though they will look smaller. Zooming in — setting the longer distance to the lens — will work as a magnifying glass.
Each zoom lens has its range of such distances. If you don’t want to get lost in figures and professional terms, just divide the largest point by the smallest one, and you’ll get the zooming ability of the lens.
For example, if the range is 18-36 mm, this model can zoom an image 2x. A lens with parameters 60-600 mm makes a picture 10 times closer and can already be considered as a telephoto lens.
Types of zoom lenses
- Wide-angle zoom lenses, as the very name implies, allow keeping a wide field of view while magnifying the image. This model doesn’t have a crop effect, but you can cut out the unnecessary parts by resizing your ready image with the help of special software.
- Fast lenses. These models have wide apertures and let a lot of light in, hence a photographer can set up a fast shutter speed, enhancing the sharpness of the pic.
- Slow lenses. Quite logically, their aperture is narrow, so they need slower shutter speed to let in more light.
- Fixed zoom lenses. This type has a constant aperture.
- Variable ones. Their aperture is marked by two figures, something like F/4 – 5.6. The first number signifies the maximum F-stop at the smallest focal length (this parameter is also given on the lens’s body). The second one corresponds to the widest aperture when the lens is at its furthest point from the sensor.
- Telescopic or telephoto lenses. Strictly speaking, it’s a separate type of lens, but they are very similar to zoom ones. They function the same way, but if an average zoom is about 2-3-4x, telephoto models can reach 10x magnifying or even more.
- Parfocal and varifocal lenses. The former keeps its focus while changing the focal length, the latter needs an additional setting up and focus adjustment while zooming in and out.
Advantages and disadvantages of zoom lenses
Zoom lenses are crucial for macro shooting. They also come in handy at sports events or while shooting wildlife, when a photographer can’t approach their “models” physically.
Another point: this lens type allows changing a focal length (an angle of view) in a wink, without changing your position or lenses. It means, you can also carry less equipment and travel light, as a photographer’s backpack is always full and there is never extra space for a dozen lenses.
As for the drawbacks, there are only two of them. Every zoom influences the sharpness of the photo, so you have to either set up a slow shutter speed, or buy a fast lens. This leads us to the second disadvantage: such camera details may be quite costly.
Deciding on a zoom lens to buy, take into account your budget limits and your favorite style of photography. If you fancy portraits or landscapes, such type of shooting equipment may be a useless waste of money, but it’s a real must-have for a journalist or a wildlife explorer.