INTRODUCTION

Here's a fascinating and highly useful accessory for your microscope, which you can make for less than one U.S. dollar. The simple microspectroscopic eyepiece described is suitable for most qualitative work, and even some semi-quantitative analyses. Let me first tell you how to make your own microspectroscopic eyepiece, and then I'll tell you how to use it and experiment with it. I first wrote about this device in 1966 (1), when inexpensive, acetate plastic diffraction grating replicas having about 13,400 lines per inch first became commonly available. Since that time, holographic diffraction grating replicas have become available at very reasonable cost, allowing for improvements in performance, with no increase in cost.

First of all, you will need an eyepiece with a focusing eyelens - the kind that you probably already have for your eyepiece micrometer. It can be an older model with focusing accomplished by sliding the telescopic tubing up and down, or it can be a more modern eyepiece with helical focusing of the eyelens. Remove the graticule from the eyepiece in preparation for the modification. The microspectroscopic eyepiece consists only of a slit, and a piece of diffraction grating replica film. Refer to Figure 1, a cross section of an eyepiece with focusing eyelens, for placement of the parts.

ASSEMBLING THE SIMPLE MICROSPECTROSCOPIC EYEPIECE

The Slit: The slit is made from a double-edge razor blade, and a piece of cardboard or a washer. Cut a round piece of thin cardboard so that it will lie on the eyepiece diaphragm, or on the eyepiece graticule mounting shelf. A U.S. 5¢ piece or an English sixpence coin makes a perfect template of correct size for diaphragms of older eyepieces. Cut a rectangular opening in the disc - see Figure 1. There is nothing critical about the dimensions of the cut-out, for it only acts to support the razor blade pieces.

click image to enlarge (374K) Figure 1

Next, snap a double-edge razor in two, using a couple of hemostats or long-nosed pliers - and don't forget to wear eye protection; a tin snips works even better. Then, snap one of the long halves in two, put the two cutting edges face-to-face to form a narrow slit - say, about 0.2 mm to begin with, and tape or glue them to the cardboard (I used double-sided sticky tape). See "D" in Figure 1 for placement of the razor blades on cardboard disc, "C." You might want to make a couple of these slit assemblies, with different slit widths. The narrower the slit, the greater will be the spectral line resolution, but the less light there will be, necessitating a higher wattage lamp.

Place the slit blade-side-down on the diaphragm of the eyepiece. You can paint everything flat black, if you want to, but if you use "blued" blades, this will not be necessary. I have been having trouble finding blued blades recently, so, for my most recent version, I used the more commonly available stainless steel blades. I used a pair of tin snips to cut them to size, and trim them.

Figure 2 shows all of the parts that you will need to convert any eyepiece with a focusing eyelens, including washers, razor blade, flat-black paint, and gun blue; a completed razor blade slit mounted on a blackened washer is also shown in place on the graticule mounting shelf of an Olympus eyepiece. For the Olympus BX-51 polarizing microscope I am currently using, a WHI0X-H/22 high-eyepoint eyepiece was converted. The graticule size for this eyepiece is 24 mm. I looked in my baby food jar of miscellaneous washers for one of that size and the closest I found was 1-inch diameter. I turned this down to 24 mm in my miniature lathe. Incidentally, a U.S. quarter (25¢ piece) is just over 24 mm (24.12 mm-24.25 mm), so it makes a good template for a cardboard disc.

click image to enlarge (421K) Figure 2

Figure 3 shows a couple of older eyepieces with focusing eyelenses, together with the new Olympus WH10X eyepiece. The eyepiece at the far left has been reassembled; in the middle, the focusing eyelens has been removed to gain access to the diaphragm; at the far right is the Olympus WH10X-H/22 eyepiece with a piece of holographic diffraction grating replica sitting on top of the eyelens, and in front of it, the slit is shown before being screwed back in the base of the eyepiece.

click image to enlarge (583K) Figure 3

It is not necessary to darken the washer and blades, but blackening them does cut down on internal glare. You will have to expose fresh, clean steel for the gun blue to "take." The gun blue I prefer consists of selenious acid, hydrochloric acid, and copper sulfate. I also use Kodak Dull Black Brushing Lacquer, but any flat black paint will do.