Subject:  Further details on Magnification

Magnification

The magnification of a magnifying glass depends on where it is placed
between the user's eye and the object being viewed, and the total
distance between the eye and the object. Magnifying glasses are
typically described in terms of their magnifying power, which is
equivalent to angular magnification (this should not be confused with
optical power, which is a different quantity). The magnifying power is
the ratio of the sizes of the images formed on the user's retina with
and without the lens.[3] For the "without" case, it is typically
assumed that the user would bring the object as close to the eye as
possible without it becoming blurry. This point, known as the near
point, varies with age. In a young child it can be as close as 5 cm,
while in an elderly person it may be as far as one or two metres.
Magnifiers are typically characterized using a "standard" value of
0.25 m.

The highest magnifying power is obtained by putting the lens very
close to the eye and moving the eye and the lens together to obtain
the best focus. The object will then typically also be close to the
lens. The magnifying power obtained in this condition is MP0=1/4 Φ+1,
where Φ is the optical power in dioptres, and the factor of 1/4 comes
from the assumed distance to the near point. This value of the
magnifying power is the one normally used to characterize magnifiers.
It is typically denoted "m×", where m=MP0. This is sometimes called
the total power of the magnifier (again, not to be confused with
optical power).

Magnifiers are not always used as described above, however. It is much
more comfortable to put the magnifier close to the object (one focal
length away). The eye can then be a larger distance away, and a good
image can be obtained very easily; the focus is not very sensitive to
the eye's exact position. The magnifying power in this case is roughly
MP=1/4 Φ.

A typical magnifying glass might have a focal length of 25 cm,
corresponding to an optical power of 4 dioptres. Such a magnifier
would be sold as a "2×" magnifier. In actual use, an observer with
"typical" eyes would obtain a magnifying power between 1 and 2,
depending on where lens is held. An older person might obtain an
actual magnifying power of 8 or more with this lens, however, due to
the eye's longer near point distance.

Enjoy,

On Oct 13, 10:18 pm, otisbr...@embarqmail.com wrote:

Salmon Egg schreef:

Bill, Andy only wants his magnifiers qualified, nothing more nothing
less and if possible in a simple way.

I could explain more but Andy wants it simple.

If you want to calculate the magnification of the combination
eye-handheldmagnifier, there is more to explain.

Jan (normally Dutch spoken)