Talk:Magnifying glass

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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=¼Φ+1, where Φ is the optical power in dioptres, and the factor of ¼ 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=¼Φ.

A diagram of these two cases would really be helpful.

--Erland Lewin 20:40, 21 October 2007 (UTC)

[edit] Creation

It would be nice to know how magnifying glasses are made to have that concave shape. Is there a section in a "glassmaking section" or what? —Preceding unsigned comment added by 41.241.43.175 (talk) 14:26, 21 January 2008 (UTC)

I think the claim "magnifying power is the ratio of the image size on retina with and without lens" conflicts with the claim that "magnifying power depends on the distance from eye to lens".

if the power is defined as the ratio, the ratio is fixed as long as the object-lens distance is fixed, since the virtual image size is fixed.

yes, normally we do want to put our eyes closer to the lens, but that is only in order to have a larger view angle, because if you view through the lens from a distance, you would be able to view only a small portion of the virtual object----- just imagine viewing a real object through a small hole in a black wall. the area of the lens is the small hole. I think the author mixed the idea of the "actual size of the retina image" with the concept of "ratio" when defining the magnifying power