Astronomy gear and microscopy

I wanted to show the kids the grooves on a CD.  With the medium magnification objective on our microscope, one could just see shimmering graininess.  And I couldn't get the highest magnification objective to focus in on the graininess.  I think the problem may have been that the condenser light couldn't go through the CD, and so I was lighting it with a hand-held flashlight, and that objective has to go so close to the object that blocked the light.  So I got out my 6mm TMB/BO planetary eyepiece (equivalent to about 40X as a microscope eyepiece), popped it in a 1.25" - microscope adapter, and went back to the medium magnification eyepiece, and while we couldn't see it too well, it was obvious that there were pits, and that they were arranged in a line-by-line pattern.

That "1.25" - microscope adapter" is home-made, of course. I cut a 1" segment of 1.25" poplar dowel. I then drilled out the inner 1" of it with a Forstner bit, making a wooden tube with 1/8" walls. I cut a 1.5" segment of some 1.25" ID aluminum tubing (well, actually, a little less than 1.25" ID--I had to sand it out). I then nested the two, with the wooden tube sticking out of the bottom of the aluminum tube, and the aluminum tube extending on top about 1/2" past the top of the wooden tube. (See diagram: gray is aluminum and brown is wood.) They fit snugly, but I put in a couple of drops of CA glue for safety.

The whole assembly then fits around the focuser tube of the microscope, with the top of the wooden tube being flush with the top of the microscope's focuser tube. Eyepieces then fit in the aluminum collar that sticks out on top. The nice thing about making the adapter fit around the focuser tube instead of the more obvious inside is that it doesn't contribute any vignetting.

Of course, it would have looked a bit neater to make the inner tube of aluminum. But ordering an aluminum tube would cost about $8, while a dowel cost $4, plus I wanted the dowel for another project. Moreover, there is an advantage to using a wood inner tube--it won't scratch the outside of the microscope focuser tube as much as metal would. I suppose PVC could have worked as well, but the closest I could find in PVC was 1.29" OD, and I didn't relish the thought of sanding that down to 1.25" OD to fit inside the aluminum tube.