
Formula
review
The following
two formulas apply to both mirrors and lenses:
The greatest
difficulty is in remembering the signs of the variables.

focal length

object distance

image distance

concave mirror

positve

always
positive

positive,
if on the same side as object (real)
negative, if on the opposite side as object
(virtual)

convex mirror

negative

always
positive

negative,as
all images are virtual
and on the opposite side as object (virtual)

convex lens (converging)

positive

always
positive

positive,
if on the opposite side as object (real)
negative, if on the same side as object (virtual)

concave lens (diverging)

negative

always
positive

negative,as
all images are virtual
and on the same side as object (virtual)

Truth's
for both lenses and mirrors
Image
distances are always negative for virtual images
and positive for real images.
Object
distances are always positive.
Real images
are always inverted and virtual images are
upright.
Examples Lenses'
index
