Given all details such as focal length , aperture etc , how can i find the size of a point on a paper that is at a given distance from a mobile camera ? Or vica versa , the distance required to resolve a point of a given size ?
- Take a picture of a sheet of ruled/squared paper.
- Open the photo in an image viewed/editor
- Measure the distance in pixels between two lines
- Divide the physical distance (in mm/inches...) between two rules by half that value. This will give you an estimate of the smallest thing you can see in a picture, if the lens is good enough for the sensor.
You can also find lens test charts on the web that may tell you a bit more about your camera.
No. You can't know this from the technical specs you are thinking of. The resolving power of a camera system depends on the way the lens is built and the properties of the recording medium — and other factors such as lighting and atmosphere.
You may be able to get some details of the recording medium — the sensor — from camera specs, but not enough to be really useful in practice. And for lenses, the resolving power is characterized by testing, not calculated in theory.