Last month, iPhone 15 line up had been released. Especially for iPhone 15 Pro Max, it came with 5x optical zoom using tetra-prism setup which would be similar to periscope lens on S23 Ultra. However, when I tried them at the store, the image quality at the tele range is not very impressive. Looking at the specs the Pro Max line up have the following

• Main
  • 48 MP 1/1.28" (10 x 7.5 mm), crop factor of 3.46
  • 24 mm f/1.78
  • True focal length 6.94 mm
  • DoF equivalent f/6.15
• Wide
  • 12 MP 1/2.55" (5.6 x 4.2 mm), crop factor of 6.19
  • 13 mm f/2.2
  • True focal length 2.10 mm
  • DoF equivalent f/13.62
• Tele
  • 12 MP 1/3.5" (4.5 x 3 mm), crop factor of 8
  • 120mm f/2.8
  • True focal length 15 mm
  • DoF equivalent f/22.4

It make sense that for tele, it need to have smaller image sensor to reduce the focal length. But this also decrease amount of light the sensor can capture. Thus, the noise is increased. So in low light, to have any usable telephoto, heavy noise filtering is applied. This caused a lot of detail to be lost

Last year, LG innotek teased 4x - 9x optical zoom. But it is likely a trade off between continuous focal range, and aperture, and I do expected smaller on 9x end. Assume best case, where we use the same camera lens specs of Sony RX100 VII of 24-200 mm f/2.8 - 4.5 then we will lose the light about 1.33 stop. So either they make the sensor area larger by 2.5 times, or they need to better design their lens

Let’s take a look at S23 Ultra camera telephoto setup. They have 3x f/2.4 (69 mm), and 10x zoom f/4.9 (230 mm). They did this to combat the aperture problem by using prime lens. But anywhere in between 3x, and 10x it will be a digital crop of 3x sensor. So at 9x zoom, your image is probably look like garbage before snap back to acceptable image at 10x

But since the smartphone chassis space is at a premium, they probably can’t realistically have better low light performance with the small compact camera design. The most camera on a smartphone is 16 (by Light L16 Phone). But that one is non-practical anyway, and they can’t just keep adding camera. So what they can do to improve the telephoto performance on a smartphone?

I have a few ideas that came to mind

• Xaomi 12S Ultra Concept, which just expose their main camera with a lens mount. Basically convert it to a mirrorless camera
• Third party lens, Moment lens is a good example of this. They have 58 mm zoom over original 24 mm main camera. So it might be possible to engineer a zoom lens version for this. But I would not imagine the lens size
• Minolta RD-3000 has a dual chip sensor by splitting the image into 2 parts at 90 degree angle. This has the potential to have a larger sensor in a small enclosure. But I don’t know the practicality of this