Tools for appreciating flowers May 26 2015, 0 Comments
I’m going to go off on a tangent before I discuss materials for botany studies with older elementary children. I’ve been researching an important tool for botany studies, a hand lens.
A hand lens (aka pocket magnifier) is very useful for botany studies. Many flowers have parts too small to see without magnification, and there are even whole flowers that are too small to see without this help. Regular magnifying glasses are usually 2-3X magnification, but what you need for botany is something in the 4X to 5X range. With that you can see the texture of stigmas and even the larger pollen grains on anthers.
In years past I have been able to purchase 5X glass hand lenses. The lens folded into a plastic case that protected it while it was being carried outdoors. When I tried to find more of these lenses, I found they were no longer available. I searched the Internet, especially Amazon, looking for a replacement and ordered several to try. Here’s what I found.
The only hand lens that had the magnification described on Amazon was the Bausch and Lomb 4X folded pocket magnifier, which cost about $14. I’m now carrying that one in my pocket as my personal lens, but that is a bit pricey for a classroom set. I found that the inexpensive lenses on Amazon were not as advertised. One that was listed as a 4X was actually a 2X. One with glass lenses came with a large scratch on the lens, and its magnification was half of the description. A “bug loupe” that was labeled 5X is actually closer to 3X, and it focuses only when held above the surface, not when resting on its clear plastic housing, which one presumes was there to contain the bug. My basic message: Let the buyer beware when it comes to inexpensive hand lenses.
To tell the magnification of a simple lens, first measure its focal length. You can do this by focusing an image of a light fixture or the scene outside a window onto plain paper. Then you measure the distance between the paper and the center of the lens. If you measured in inches, divide that measurement into 10. If you measured in centimeters, divide that measurement into 25. The result is the magnification. This means that a 5X lens should focus about 2 inches or 5 cm from the paper. A 4X lens should focus at 2.5 inches, and so on.
In the end, I decided that I will have to settle for plastic lenses, although they will scratch easier than glass. Acorn Naturalists has a small 5X lens for about $4, so you can get several for botany or other work. The lens is about an inch in diameter, which is easier for children to use than the narrower 10X lenses. Ten times is more magnification than one really needs, and the short focal length means that you cut off the light as you bend close to look.
With all these lenses, you need to hold the lens close to your eye and either bend down or bring the object up until it is in focus.
I hope this information helps you find the lenses you need for botany and other outdoor observations. If you have found a better alternative, please let me know.