Magnification labels for stand magnifiers: Always misleading and usually unachievable

Illustrating the conditions for nominal magnification. Stand magnifier for which the object is located at the primary focal point, F. The vergence of light exiting the magnifier is zero, the image is at infinity, and the accommodation or add required for an emmetrope to view the image is zero. The image subtends angle ω’ at the entrance pupil of the eye.

Object of height, y, is located at the reference seeing distance, d, and subtends angle ω_d at the entrance pupil of the eye.

Illustrating the conditions for trade magnification. Object (height y) is located so the image (height y’) is at an image distance, l’, equal to the reference seeing distance, d, from the SM and subtends angle ω’ at the entrance pupil of the eye. The SM is held as close as possible to the eye (h ≅ 0), and the image is viewed with +4.00 D in addition to the distance prescription.

Illustrating the general conditions for relative magnification. The SM, located at distance, h, from the entrance pupil of the eye, is placed on the page (object). A virtual image is formed at image distance l’. The observer uses an add (or accommodation or uncorrected myopia) to view the image, which subtends angle ω’ at the entrance pupil of the eye.