Digital zoom is something you usually achieve by spreading two fingers on the screen to make a subject look bigger. It does not change the optics or the position of the lenses of the camera. It just crops what light falls on the
sensor, so it doesn’t cover the full area. In other words: you don’t use all the sensor, and you typically get a smaller picture.
Ever since the idea of digital zoom came to the earliest digital cameras, it has been shunned by people who think they are in the know. If you try to take a photo of your child on a sailing boat far out at sea, it simply will not get better just because you spread your fingers on the screen to zoom in. The picture will have exactly the same number of pixels as if you had taken a full photo and afterwards cropped it in post processing.
Knowing that, there are still a few cases where digital zoom can have some use.
To start with, the photos will usually be smaller. If you have a problem with space, it may be good to remove the parts of the photo you do not want already at the beginning. You can of course remove redundant space in post processing as well, but many current programs, like Adobe Lightroom, google Snapseed or Apple’s Photos, pride themselves with non-destructive editing, which means you can go back to the original. If you crop a photo using non-destructive editing, it will not be smaller than the original. It will actually be slightly bigger, as the program needs to store information of what has been cropped.
Another time to use digital zoom is to get exposure right. Imagine that there is a hedge with plenty of dark green leaves and a bright flower in the middle. If you take a photo of the whole hedge, the phone will adjust the exposure after the bigger part of the photo, the dark green leaves, and the flower may be overexposed. However, if you use digital zoom to make the flower bigger, the flower will be more prominent in the photo, and the camera can adjust exposure to the flower. There are other ways of solving the problem with a light flower on dark background, but sometimes digital zoom is a perfectly fine solution.
Yet another time to use digital zoom is to get focus right. If you try to focus on a tiny flower and ignore a distant background, it may be difficult to convince the camera to focus on the flower. With digital zoom, you can make the flower occupy a larger portion of the picture, and the camera may realise where to focus.
In the first photo, the red flowers are out of focus, as the camera tries to focus on the big green background instead. In the next photo, the photographer used digital zoom, to convince the camera that the flowers were the subject. In doing so, he got sharper flowers, but he had to accept a loss of resolution.
Even if the resulting photo will have a lower resolution, it may be good enough for your needs.
Experience: Find a situation where you do not need the full frame of a
scene. Take one photo with digital zoom and one without any zoom. Crop the photo you took without zoom. Compare the two photos and see what differences you find in exposure and detail.
Zooming with your feet
There is an expression for photographers that use big cameras with fixed lenses that do not zoom: “The photographers zoom with their feet.” This means that they walk closer when they want to zoom in, and they walk further away when they want to zoom out. When using phone cameras, that is often exactly what one has to do, if one wants to avoid digital zoom.
Some photographers say that to get a good photo, you should go really close. When you got as close that you think you can properly go, then you go a little further. And after that you get closer again.
That is an excellent piece of advice if one has a lens that can handle it. In many situations, phone cameras can be used in this way.
When it comes to close up portraits, however, phone cameras are notoriously bad. No matter how beautiful your partner or model is, if you take a real close up, the phone camera will distort the proportions, so all beauty will be gone.
Not only that, but with real close ups, you will see all the imperfections of the skin, and many do not appreciate having those revealed in detail. When it comes to portraits, it is better to keep your distance.
Here are three photos that tell three different stories after the photographer zoomed with his feet. The first is a church wall with a cemetery next to it. The second tells the story about a few tombs in the setting of autumn leaves. The church building is no longer visible, and it is no longer part of the story. The last picture is a close up of the head of a statue. The tombs in the background make it clear that the lady is grieving and not just resting.