Recently I installed a new work desk, and found I needed a new magnifier for it. So I went about shopping on the internet for a magnifying lamp of sorts. I used to have one on my workbench where I used to be employed, and it worked very well for surface mount soldering, but I didn’t know much about it, other than what it looked like. So I set out shopping.
I found that each store or seller described their magnifiers in different ways. Some listed their Diopter, others the magnification, and still others the percentage of increase in size. So how do you compare a magnifier with a Diopter of 16 with another that has a power of 3x against another that claims a 100% increase in visual size? Well that got me to doing some research on the internet as well, and I came across several websites that had charts, and formulas that allowed you to convert one to the other, and I found that the charts were very easy to use and most helpful. One aspect of magnification that is particularly important to modeling is the focal length. When you are magnifying with a single lens, the focal length is fairly set, with a little play perhaps but within a range that cannot be changed. So whether you prefer to wear a pair of eyeglass magnifiers, or work with a large magnifier over your bench, focal length becomes very important. As in, the distance the object you are viewing is from the lens.
Here is a chart like the one I found to be so helpful:
Diopter | Focal Length | Power | Increase in Size |
3 | 13" | 1.75X | 75% |
4 | 10" | 2.00X | 100% |
5 | 8" | 2.25X | 125% |
7 | 5.5" | 2.75X | 175% |
8 | 5" | 3.00X | 200% |
9 | 4.5" | 3.25X | 225% |
11 | 3.75" | 3.75X | 275% |
13 | 3" | 4.25X | 325% |
16 | 2.5" | 5.00X | 400% |
18 | 2.25" | 5.50X | 450% |
20 | 2" | 6.00X | 500% |
I originally thought I might like to have something in the 3x to 5x magnification power, but after looking at information on the chart, I saw that a diopter of 16, equal to a magnification of 5x, had a focal length of about 2 to 2.5 inches! Well that might be fine for looking at stamps, or coins, but for working on models, it just would not do. So in order to get my tools in between the lens and my work, I needed a focal length of at least 7 or more inches. So, I came across a nice boom type lighted magnifier with a lens of 5 inches in diameter, and a diopter of 3. So looking that up on the chart, I discovered that it had a magnification of only 1.75x, but a focal length of up to 13 inches! This gave me a percentage of enlargement of only 75%, but I needed the focal length to work under the lens, so I took a chance on it and bought it.
I was pleasantly surprised to find that I had plenty of room to work under the magnifier and never had to move it once I had it set. And because it had the round florescent light around the lens, the work was very well lit, and even though the magnification sounds low, I found the object appeared very large to my eyes, and the smallest details were easy to see and work on.
So depending on what you want to use a magnifier for has a great influence on what power you will need. And seeing that most of us are modelers who want to see the small details on our train cars and structures AND work on them while under magnification, less is more. So if you are shopping for a magnifier, or are not happy with the magnifiers you have, check out the chart and let it help you decide.
Russell Kingery
Modeling N scale Norfolk Southern and CSX in VA
