Do mobile cameras ever vary f stops?

Question

I've been trying to get my head around the camera in my newly-bought Chinese mobile phone.

I wonder how focusing actually works in these kind of phones. I imagine that in the standard context of auto focus or touch focus, when you actually focus on different areas of a picture, there should he some sort of adjusting movement between various lenses elements, and different f stops would need to be used to change aperture size, and to achieve differential focus.

Well, for this phone, in one compose, I focused on my hand few inches away and took the same picture 6ft away, focusing on a closet. I compared the EXIF data of both JPGs and found that the f stop of F2 is used in all of the pictures all that changes is ISO and exposure time. Is this normal for a mobile phone camera?

Answer 1

different f stops would need to be used

No. Focus is, as you say, achieved by moving various of the lens elements around. Aperture changes are achieved by closing the diaphraghm and has nothing to do with focusing. They are two entirely separate concepts.

That all said, most if not all mobile phone cameras don't have a diaphragm, so they can't change aperture. This generally isn't a problem as there are two reasons you might want to stop down:

1. To increase depth of field. Not an issue with mobile phone cameras which have very high depth of field anyway.
2. To reduce the amount of light reaching the sensor. Not an issue in 99% of cases for a mobile phone camera, which has such a small sensor you're generally trying to more light onto it, not less.