When using magnifiers, be aware of distortion, chromatic and spherical aberration errors that can occur. Distortion is a defect in a lens where images of straight lines appear curved. Chromatic aberration errors occur when the lens cannot focus light of different colors at a single point, causing a blue-red image. Spherical aberration errors cause rays to focus at different distances.
Different types of lens systems offer varying levels of correction for these problems.
The simplest type of lens is the single aspheric lens
. This lens is designed for small powered magnification because it is a single lens with a series of different curves on the surface for sharper focus over the entire surface.
consists of two lenses with air space in between them. This lens system is inexpensive but does not offer much distortion or color correction.
are made of a single lens with a grooved diaphragm around the circumference. This groove allows for sharp images at higher magnifications.
is the last type of lens system and is also called a Hastings
. The Hastings lens consists of three lenses cemented together, providing the sharpest color-corrected image.
What is the proper way to use a magnifier?
To use a loupe, hold the lens close to your eye and move the object you are looking at close until it's in focus. For linen testers, simply place the magnifier on top of the object and move your head closer to the lens for larger viewing.