Which Magnifier?

ARTHUR H GAEBEL, INC.

Which magnifier is right for you?

Generally speaking, selecting a magnifier is a matter of personal preference. The form, the magnification, the weight and size of the image are what make up the preference for most people. In order to get the most out of the magnifier you decide on, there should be some science involved in that decision. Part of the selection process should involve four basic questions:

What tools are going to be used on the job?
What the size and character of the subject is?
What the surface of the object is like?
What limitations do I have in the size of the magnifier?

In order to make a good decision, you need to consider some attributes of the magnifiers you are considering. The number of elements determines many of the other considerations. A single lens is satisfactory for low powers. Higher power magnifiers require two or more lens elements for improved resolution and correction of colors or other aberrations.

The working distance is the distance from the magnifier to object being viewed. This distance is an important consideration with regard to the type of work being done under the magnifier. If your work requires the use of tools, a magnifier with a high working distance will allow enough space to both use the tools and comfortably view the object. Small working distance magnifiers with higher power are preferred for close-up inspection work.

The area seen through the magnifier is the field of view. As the power increases, lens diameter and field of view decrease. At 5 power (5X), field of view is about 11/2". At 10 power (10X), it is about 1/2". Usually, it is best to use low power for scanning surfaces and high power for checking small areas.

The depth of field is the distance between the closest and furthest points at which a magnifier in a fixed position stays in focus. It is a valuable feature for examining uneven surfaces such as rock specimens. The depth of field decreases as the power increases.

When a magnifier offers a "coated lens" , that means that the lens surface has special anti-reflection coatings that reduce light loss and are particularly useful for low light level applications. This should be considered if you are going to be using a magnifier where the light is limited.

It is assumed that 10" is the closest distance you can focus for comfortable vision. An object only 1" from your eye would be 10 times larger, but out of focus. A magnifier's function is to make this close view possible. Since a 1" focal length lens brings clear vision down to 1" from the eye, an object at this distance is clearly seen and appears to be 10 times closer than it does when viewed from 10" away. Such a magnifier is commonly called a 10X or 10 power. Actual magnifying power will vary slightly, depending upon working distance, eye relief distance and the characteristics of the observer's eye.

The magnifying power of a lens depends on its focal length. The focal length, in turn, depends on the lens curvature; the greater the curvature, the shorter the focal length and the greater the power. In the design of a simple, inexpensive magnifier, the lens diameter will typically decrease as the curvature increases to provide higher power. Conversely, as the curvature is decreased to lower the power, the diameter generally increases with a resulting increase in viewing area. In addition, distortion generally increases with an increase in curvature. Thus, a magnifier with a large diameter typically offers more viewing area and less power. So, both wide field of view and high magnifying power cannot be incorporated into a single design without elaborate, weighty, high cost lenses.

So, if you are looking for the perfect magnifier for every job, you can stop looking. However, you should look for the right magnifiers for the tasks you do. Adding the science to the decision will allow you to make the right choice and allow you to see the amount of detail needed for the best results.