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I came across this thread, and I thought I'd add what I've done to an old eyepiece to make a Celestron FirstScope a big finder.
It's an old Celestron 25mm Kellner. I found the focus of the eyepiece sat inside the main body, a little infront of the field lens. Using a little high school geometry, I gauged its center and drilled four tiny holes into the eyepeice at the centre points to the place of its focus. I drilled an extra hole next to each centre hole to loop some copper wire.
The copper wire can from an old telephone lead. I found this to be the thinnest at my disposal, at around 0.1mm in diameter. The wire is looped around one pair of holes, threaded through the eyepiece and wound around the opposing pair of holes. The process is repeated for the other set of holes. Epoxy glue holds the loops in place.
The first picture shows the image through the eyepiece and the second wires in place within the eyepiece with the 1.25" barrel removed.
It is unilluminated, but in an f/4 scope, no illumination is necessary as the background sky glow is sufficient to show up the crosshairs.
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