How to process 2 photos with a 2 focal length from the same smartphone?

Hello All,

I am using a smartphone whose focal_length is 3.85mm and i use analog_exif to retrieve the exif info.

I took one photo (A) and i see the "Focal Length in 35mm" is 35mm.

I took another photo(B) of the same object but this time i "zoomed" it. The "Focal length in 35mm" is then 108mm.

As the zoom is only a digital magnification i want to reduce the size of the photo B by a factor 108/35.

Then for calculations i will only use one focal length: 35mm.

Is my My reasoning correct?

Thank you for you help Alvaro

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