"how to" tutorial series
How to Make and Use a Simple Microspectroscopic Eyepiece
||John Gustav Delly, Scientific Advisor, Hooke College of Applied Sciences, Westmont, IL
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
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.
THE SIMPLE MICROSPECTROSCOPIC EYEPIECE
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
click image to enlarge (374K)
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 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)
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.