focal length VS distance between pinhole and virtual image

focal length VS distance between pinhole and virtual image

by Loic Nathan Thome Busson -
Number of replies: 3

How is it that here the focal length (f) is equal exactly to the distance between the center of the Lens and the real image plan? That's not always the case no? For me, it's true iff the object is situated far far away (+oo). In which case, the real image plan is indeed located at the focal plane. Otherwise it's wrong. So for me, instead of f in the formula we should write OC. Am I wrong?

In reply to Loic Nathan Thome Busson

Re: focal length VS distance between pinhole and virtual image

by Semih Günel -

Hi Loic,

I agree lens center is an unexpected name for the focus of the lens. Here, you can replace the term lens center with pinhole or focus of the lens, and everything should be fine.

The next image depicts how it works in reality, you can see the lens center is the same point as the focal point. In modern cameras, there is a pinhole + lens, and the lens is put in such a way the that lens center (focus) and pinhole are at the same point.