# Optics - how a lens distorts the image

If we consider a small object of length $b$ that is placed flat along the axis of a concave mirror, how will the image produced be different from the object?

I know that a lens will magnify or diminish an image, depending upon the position of the object with respect to the lens. However, that occurs only to the dimension normal to the axis of the lens.

Why should the image produced, in the case above with object of length $b$, be any different from the original object?

• Does your object have any thickness? – SchrodingersCat Oct 24 '15 at 11:49
• @Aniket It doesn't. It only has a length along the axis. Nothing more. – Gummy bears Oct 24 '15 at 11:58
• If it's got zero extent perpendicular to the optic axis, then all you have is the longitudinal compression, and all you can see in any 2-dimensional plane is a dot. No distortion is possible. – Carl Witthoft Oct 24 '15 at 21:08

• This is unclear, and does not appear to describe distortion. If each point on $b$ is mapped from $y_j$ to image height $Y_k$ linearly, then you have pure magnification. It's only because (for simple lenses, etc) the mapping is nonlinear that you get distortion. – Carl Witthoft Oct 24 '15 at 21:06