These days, when looking at smartphone camera specs, optical zoom has increasingly become a major talking point by phone manufacturers. That's because in the past, phone cameras have only been able to use digital zoom, but now technology has made optical zoom a reality.
For those who don’t know the difference, this can be confusing, and some have been left wondering which one is best.
The zoom function serves to decrease the field of view in the frame and magnify the subject of interest. On an ordinary camera with a zoom lens, optical zoom works by mechanically moving the glass elements within the lens to magnify the image. Digital zoom, on the other hand, is completely software reliant.
Although what is referred to as optical zoom on smartphones works differently, phones that use it tend to produce better quality pictures when zoomed in, than those that use digital zoom.
In order to understand optical zoom on smartphones, we first need to look at what came before it－digital zoom.
Digital zoom is not exclusive to smartphone cameras. Many point-and-shoot cameras are known to have optical zoom AND digital zoom. But because of size restrictions, digital zoom is mostly prevalent in mobile phone cameras.
How does digital zoom work?
Strictly speaking, digital zoom is not really zoom at all but rather a digital simulation of optical zoom. With digital zoom, the camera basically crops the image and then resizes it to fit the frame again.
Digital zoom is actually one of the reasons why some smartphone manufacturers pack their cameras with a lot of megapixels. The more megapixels a camera has, the more the picture can be blown out without an overly noticeable reduction in picture quality.
What’s the disadvantage of digital zoom
Unless it’s a really minor zoom in, you are bound to notice a loss in picture quality when using digital zoom. Guaranteed.
Just think about it. If you take a photo with a typical 4000 x 3000 (12MP) resolution and crop it down to 3000 x 2000 (6MP), you will definitely lose picture quality by trying to stretch it to fit the dimensions of a 12MP photo. This is because you will have basically halved the resolution of the photo and stretched it out despite not having enough pixel data to fill the frame.
Also read: The Truth About Smartphone Camera Megapixels
Smartphone manufacturers have come up with different techniques to fill in these pixel data gaps. One of the ways in which this is done is through interpolation. The camera’s algorithm looks at neighbouring pixels and makes calculated guesses to determine what colour pixel is needed to fill the gap.
It is this combination of real pixel data and software interpolated pixels that provides the final, digitally zoomed in picture. The results of this vary from manufacturer to manufacturer depending on the sophistication of their algorithms but it’s usually not that great. You’re still losing organic quality!
Not ones to give up on including better native zoom capabilities on their devices, smartphone manufacturers found a way to improve how their camera zoom.
On a traditional camera, a fixed lens (otherwise known as a prime lens) allows light through and bends it to a focal point on the image sensor. The distance from the centre of the lens to where the light rays are converged to a focal point on the sensor is known as the focal length, measured in millimeters. And because the lens is fixed and doesn’t move, the focal length will always be the same.
For example, a 50mm lens will always have that focal length. If you need to get a closer shot, you have to either get closer to the subject or change to a lens with a longer focal length.
A zoom lens, on the other hand, is made up of several glass elements inside that move back and forth in relation with each other in order to magnify the image (zoom in) or make it smaller (zoom out). As these glass elements move, the focal length changes.
For example, a lens that is said to 18-55mm means that it can change its focal length from 18mm (wide-angle shot) and zoom in to a 55mm focal length, which gives a narrower field of view.
How does optical zoom work on smartphones?
Optical zoom on smartphones
When it comes to smartphone size, thin is king, so you won’t find devices with protruding zoom lenses. Others like Samsung have tried in the past with phones such as the Galaxy Zoom that had a 10x optical zoom lens that extended from the rear, but that type of camera didn’t quite catch on.
The solution? Multiple cameras.
It is very common these days to find two, three, or more cameras/lenses on the back of a smartphone. It may seem redundant but each of these cameras is different and serves a particular purpose.
Typically, in a triple-camera setup, you’ll find a camera with a telephoto lens, a wide-angle lens, and an ultrawide lens. These lenses all have different focal lengths depending on the field of view (also known as angle of view) they provide.
When you zoom in or out, the phone will automatically switch to the camera with the lens that will give you the shot you want. In other words, if you want to zoom out from the standard wide shot, your phone will switch to the ultrawide lens. If you zoom in, the telephoto camera will kick in automatically.
How far you can zoom in on your smartphone camera is determined by the focal length of the telephoto lens. Taking the focal length of the telephoto lens and dividing it by the focal length of the wide-angle lens will give you the zoom range of the camera.
For example, if a phone has a telephoto lens with a 52mm focal length and a 26mm wide-angle lens, this gives you the zoom range of 2x optical zoom.
In my post ‘Do Smartphones Really Need Multiple Cameras?’, I discuss in further detail what each camera does and how they work together. Not only does the article cover optical zoom, but it also sheds light on the other cameras that are on today’s smartphones. Definitely worth checking out.
Is it actually optical zoom?
No, not really. Unlike with traditional camera zoom lenses, smartphone optical zoom does not have any actual moving glass elements, so it is difficult to classify it as such. However, it does work through the optics of all the cameras. I guess it was with that in mind that smartphone companies decided to market it as optical zoom.
Because it switches between cameras with fixed focal length lenses, some have argued that optical zoom on smartphones should rather be referred to as multi-camera zoom. I agree with that but I guess “optical zoom” works better for sales.
Is optical zoom really any better than digital zoom?
Yes, it is better than digital zoom but this technology is far from perfect. Optical zoom on smartphones can also suffer image quality loss.
It’s also worth noting that in most cases, the cameras on a multi-camera smartphone have different sensors. It’s not uncommon to find phones with main cameras that have more megapixels than the other cameras. So when you switch cameras, you may lose picture quality.
Smartphone manufacturers introduced what is sometimes called hybrid zoom to combat this issue. To get the best results, smart algorithms are employed to grab the data from all the cameras and use it to put together an image with as little apparent picture degradation as possible while zooming in.
No matter what you think of it, optical zoom on smartphones is far better than digital zoom. As impressive as its results are, though, due to size limitations and current technology, smartphone optical zoom doesn’t quite live up to true optical zoom. But as we’ve seen, mobile camera technology gets better and better every year. So it’s only a matter of time.
Oh, and one more thing…
I usually have steady hands but it’s a fact that the more zoomed in you are, the harder it becomes to keep your shot still. And I have personally had to deal with this many times. It makes using a tripod very imperative.
If you think tripods for smartphones are unnecessary, trust me, you’re not alone. I used to think so, too. Now I can’t imagine life without it. If you’re still unsure about it, check out these 8 really good reasons to invest in a tripod.