Here’s what I learned about cameras and phone lenses:

1. On professional cameras, the lens determines focal length and aperture, while the body controls shutter speed and ISO.
2. Aperture is written as f/x. ‘f’ is the lens’s equivalent focal length, and ‘x’ is a multiplier: the aperture diameter is the focal length divided by ‘x’.
3. ‘x’ is the denominator, so a smaller ‘x’ in f/x means a larger aperture.
4. This notation is used because, for lenses with different focal lengths, the same ‘x’ value yields similar exposure and bokeh. (This can likely be proven with trigonometry.)
5. Focal length determines the sharpest point (the focus). Aperture sets the range around that point which remains clear. A larger aperture creates a narrower clear range and more background/foreground blur, and vice versa.
6. Space limits phone cameras. They rarely use variable focal length or aperture. Instead, they switch between multiple lenses with fixed focal lengths and apertures.
7. Most flagship phones have three cameras: a moderate focal length (20-35mm) for everyday shots; a shorter one (under 20mm), ultra-wide-angle, for large scenes and macro; and a telephoto (over 50mm) for distant subjects.
8. The number of phone cameras won’t keep growing; there are only so many use cases.
9. Since phone lenses mostly have fixed focal lengths and apertures, you’re usually adjusting shutter speed and ISO. Many phones offer focal length adjustment, but it’s algorithmic; the focal length doesn’t physically change.
10. Phone cameras have small apertures, creating a large depth of field. Everything, near to far, is in focus. Phones can sense object distance. Setting a “virtual focal length” tells the software to blur objects outside that range, simulating a large aperture.
11. This simulated focal length change isn’t as good as a real physical change. The algorithm can make mistakes, especially in portrait mode. It might, for instance, blur an object in someone’s hand along with the background.

This explains my OPPO Find X6 camera’s quirks: 1x is sharp, using the 24mm main lens. 0.6x zooms out, with distorted corners, because it switches to the 15mm ultra-wide-angle lens. 2x zooms in, but image quality drops; it’s cropping the 1x image. 3x is sharp, like 1x, because it switches to the 65mm telephoto lens (same pixel count as the main lens). 6x gets blurry; it’s cropping the 3x image.

“Optical zoom” is mostly a marketing term. Not mentioning it doesn’t mean it’s absent, and mentioning it doesn’t make it significant. If the telephoto lens’s focal length is several times the main lens’s, it’s called “optical zoom.”