At first, I didn’t know how to find the focal length of my mobile camera(s). I alongwith my brother (@CuriousVidhi) made a search on the internet and came across this paper;
“Measuring the focal length of a camera lens in a smart-phone with a ruler”
Here, they have used a ruler, smartphone to actually calculate the focal length using the formulae given in the paper.
I followed it and took a picture as described in the paper (to avoid errors as we were doing it for the first time). Then, we measured the object size, pixel size and some more parameters (and got few numbers) that were to be applied in the formulae. But, I got stuck here. Didn’t actually knew how to proceed.
The above picture has been taken as described in the quoted paper.
Then, a thing stormed in my mind that when I take a photo, it gets saved in the gallery and (for some purpose) if I want to look at the details of the photo, I would simply swipe up on the photo and the details were shown.
This is how it looks in the Google Photos app. Below the name of the mobile, there are some digits shown. There I saw 3.59mm and realised that the quoted paper too had the focal length in millimetres.
Then I came to know that the focal length of my phone’s rear camera is 3.59mm
Above photo taken by the front camera.
And that of the front camera is 3.15mm.
This was our approach.
I didn’t really understand the third and fourth question/point. Can we elaborate?