The mirror formula links the object distance u, image distance v and focal length f of a spherical mirror. This calculator uses the New Cartesian sign convention: distances in front of the mirror are negative.
For a concave mirror f is negative; for a convex mirror f is positive. A negative image distance means a real image in front of the mirror; a positive one means a virtual image behind it.
| Object distance (u) | -30 cm |
| Focal length (f) | -20 cm |
| Image distance v (cm) | -60 |
| Magnification m | -2 |
| Radius of curvature R (cm) | -40 |
The image forms at -60 cm (real, in front of the mirror) with m = -2: inverted and twice the size.
Try this example →| Object distance (u) | -30 cm |
| Focal length (f) | 20 cm |
| Image distance v (cm) | 12 |
| Magnification m | 0.4 |
| Radius of curvature R (cm) | 40 |
The image is at 12 cm behind the mirror with m = 0.4: virtual, upright and smaller.
Try this example →1/v + 1/u = 1/f, with the New Cartesian sign convention.
m = −v/u.
Yes, under the New Cartesian sign convention, because the focus is in front of the mirror.
R = 2f.