How to Determine Magnification Power of Backup or Replacement Loupes
ErgoPractice News – November 2017
Recently we received a question from a customer concerned about his new pair of loupes. He had been working with 3.5x magnification for many years and ordered replacement 3.5x magnification loupes. After receiving his new loupes he was surprised to find the magnification power seemed less even though ordered the same loupe model.
There are several potential reasons, the most common of which is the working distance effect on the magnification power. If you want to work with a significantly different working distance, the magnification power of the new loupes will be significantly different.
Ergonomic Trends and Working Distance
After contacting the customer, we discovered that although the loupe model and frame were the same, the customer had requested that his working distance be increased to work with an improved posture. He was learning more about how leaning over the subject, putting the spine into a “C” shape, causes working pain which can lead to eventual injury.1 Instead of continuing to work at a working distance of 16 inches, he wanted his working distance extended to 20 inches.
Moving the working distance out did help him achieve a more ergonomic position. But as he noticed, extending his working distance from 16 to 20 inches had an effect on his achieved magnification (Figure 1).
As you know, one can naturally “magnify” an object in hand by bringing it closer to the eye. Bending closer to our subject in order to see better is the most natural thing in the world. In fact, this tendency is the reason many people work at the inside edge of their depth-of-field (the range away from your eyes where an object is in focus through magnification). If you lean into your subject, the object will appear even larger!
When he changed his working distance from 16 to 20, outwards, it had the opposite effect. It was like having an object in your hand and moving it away from your eyes, resulting in an apparent magnification “loss.” This clinician was not alone. According to our data, customers’ working distances have been steadily increasing over many years. Much of this change may be due to information about better ergonomics reaching clinicians, but also better ergonomics being taught to younger clinicians in their training. As a result, working distances are longer on average today than they were years ago.
New clinicians today, working at a more healthy (longer) working distance, are achieving less effective magnification with the same traditional loupes as their predecessors. The 2.5x “standard” from years ago is definitely in question, because longer working distance requires more magnification.2
Working Distance Effect on Magnification
This customer experienced 3.5x magnification at a focal distance of 16 inches for many years. A working distance that is closer or farther than this reference point results in a varied magnification experience.3 This apparent loss in magnification the clinician experienced when their working distance was increased is due to this distance effect.
The magnification of loupes may have remained the same, but because the subject is farther from the eye, it appears more like 2.5x or 3.0x magnification than the 3.5x magnification the clinician is used to seeing at 16 inches. Figure 1 shows the appearance of 3.5x magnification at varying working distances. It’s clear that a farther working distance gives the appearance of magnification loss.
Magnification Power of Backup or Replacement Loupes
The backup or replacement loupes should help you see the same or better than the current pair of loupes. If the working distance of the new loupes is increased by x%, the magnification power of the new loupes should be increased by at least x%.
For example, let the magnification power of the current loupes be 3.5x and the working distance of 16 inches. If the desired working distance of the new loupes is 20 inches (25% longer), then the minimum magnification power of the new loupes should be 4.375x.
This higher magnification would overcome the magnification power loss due to the increased working distance.
For more information, contact your local representative at www.SurgiTel.com/MyRep!
References:
- Highsmith JM, Vertebral Column: Backbone of the Spine, Spinal Anatomy Center, 2017; www.spineuniverse.com/anatomy.
- Chang, BJ, Microscope Magnification with the Flexibility of Loupes, ErgoPractice News, December 2015
- Chang, BJ, Magnification Power as the Key Vision Factor, ErgoPractice News, May 2014
