Learn about zoom lenses

The zoom function of a digital camera comes in two configurations: optical zoom or digital zoom. It's important to understand these two types of zoom lenses because they are very different from each other.

In the battle between optical zoom and digital zoom, only optical zoom is always useful for photographers.

Read on to find more information that can help you better understand camera zoom lenses.

When you're shopping for a digital camera, manufacturers like to try to make the purchase easy for you, especially by highlighting certain dimensions of their models, such as large megapixel counts and large LCD screen sizes. However, these numbers don't always tell the full story, especially when looking at zoom lenses on digital cameras.

Optical zoom measures the actual increase in focal length of a lens. Focal length is the distance between the center of the lens and the image sensor.

By moving the lens further away from the image sensor within the camera body, the zoom increases because a smaller part of the scene hits the image sensor, causing magnification.

When using optical zoom, some digital cameras will have smooth zoom, which means you can stop at any point along the entire zoom length to perform a partial zoom.

Some digital cameras use unique apertures during zoom, usually limiting you to between four and seven partial zoom positions.

With most digital cameras, the zoom lens moves outward, extending from the camera body when in use. However, some digital cameras zoom while resizing the image within the camera body.

Frankly, the digital zoom meter on a digital camera is worthless in most shooting situations. Digital zoom is only useful in certain situations.

Digital zoom is a technique in which a camera takes a photo, then crops and enlarges it to create an artificial close-up photo. This process requires enlarging or removing individual pixels, which can result in a loss of image quality.

Most of the time, you can use photo editing software on your computer to perform the equivalent of digital zoom after taking the photo.

If you don't have the time or access to editing software, you can use digital zoom to shoot at a high resolution and then create an artificial close-up by removing pixels and cropping the photo to a lower resolution that still suits your needs.

When looking at the specs of a digital camera, both optical and digital zoom measurements are listed with a number and an "X", such as 3X or 10X. The larger the number, the greater the amplification capability.

Keep in mind that not every camera's "10X" optical zoom measurement is the same.

Manufacturers measure optical zoom from one extreme of a lens' capabilities to the other.

In other words, the "multiplier" is the difference between the minimum focal length measurement and the maximum focal length measurement of the lens. For example:

  • If the minimum focal length of a 10x optical zoom lens on a digital camera is 35mm, the maximum focal length of the camera is 350mm.
  • However, if a digital camera offers some additional wide-angle capabilities and has a minimum 28mm equivalent focal length, the maximum focal length of the 10x optical zoom will be only 280mm.

The focal length should be listed in the camera specs, usually in a format similar to "35mm film equivalent: 28mm-280mm". In most cases, a 50mm lens measures as "normal," has no magnification, and no wide-angle capabilities.

When you are trying to compare the overall zoom range of a specific lens, it is crucial to compare the 35mm film equivalents of each lens.

Some manufacturers publish exact focal length ranges as well as 35mm equivalent numbers, so it can be a bit confusing if you're not looking at the correct number.

Digital cameras aimed at beginners and intermediate users usually only offer built-in lenses. However, most digital single-lens reflex cameras (DSLRs) can use interchangeable lenses.

With a DSLR, if your first lens doesn't have the wide-angle or zoom capabilities you want, you can purchase additional lenses that provide more zoom or better wide-angle options.

DSLR cameras are more expensive than point-and-shoot cameras, and they are generally aimed at intermediate or advanced photographers.

Most DSLR lenses do not include an "X" number for zoom measurement. Instead, the focal length is simply listed, usually as part of the DSLR lens name.

DIL (digital interchangeable lens) cameras are mirrorless interchangeable lens cameras (ILC) that also use lenses listed by focal length, rather than X zoom number.

For interchangeable lens cameras, you can calculate the optical zoom measurement yourself using a simple mathematical formula:

  • Take the maximum focal length that an interchangeable zoom lens can achieve, such as 300mm.
  • Divide this number by the minimum focal length (eg 50mm).
  • In this example, the equivalent optical zoom measures 6X.

While choosing a point-and-shoot camera with a large optical zoom lens is ideal for many photographers, it sometimes comes with some minor drawbacks.

  • Noise: Some entry-level budget cameras suffer from lower image quality due to noise when the lens is expanded to its maximum zoom capability. Digital camera noise is a group of stray pixels that don't register properly, often appearing as purple edges in photos.
  • Pincushion distortion: Maximum zoom can also sometimes cause pincushion distortion, a distortion where the left and right edges of a photo appear to be stretched. The horizontal lines curve slightly towards the middle of the frame. Again, this problem is usually limited to entry-level, cheap cameras with large zoom lenses.
  • Slow shutter response time: When using the maximum zoom ratio, the shutter response time can sometimes become slower, which can result in blurry photos. You may also miss spontaneous photos due to the slower shutter response. At maximum zoom settings, digital cameras take longer to focus on an image, which explains the slower shutter response time. Such problems are exacerbated when shooting at maximum zoom in low-light conditions.
  • Tripod required: Using a long zoom lens may result in increased camera shake. Some digital cameras can solve this problem with image stabilization. You can also use a tripod to prevent camera shake from blurring your photos.

Some manufacturers combine digital zoom and optical zoom measurements when emphasizing product specifications, thereby displaying a larger combined zoom number on the front of the box.

But you just need to look at the optical zoom number, which is probably listed in the corner of the back of the box, along with a bunch of other spec numbers. You may need to do some searching to find the optical zoom measurements for your specific model.

When it comes to digital camera zoom lenses, it pays to read the fine print. Understanding zoom lenses will allow you to get the most out of your digital camera purchase.