[Wavytone]

Hi Chris,

There are engraved glass reticles with a grid etched on them - typically at 1 or 0.1 mm spacings - used in biological microscopes, and you can find them on the net with a bit of Googling. But unfortunately you cant buy such a thing in an eyepiece ready-made.

I am fairly sure the only way you could do this is with a DIY effort - that means cannibalising an eyepiece with a lathe and some basic materials and workshop tools.

I'd start with a fairly simple eyepiece like a Plossl, Orthoscopic or Edmund RKE around 20-25mm focal length that has a ring defining the edge of the field which is accessible, and make a new barrel to mate the optics to a commercial reticles.

Lastly, there is an issue with distortion in eyepieces. Many have a lot of pincushion distortion - particularly wide-field types with apparent fields > 50 degrees.

Note that Orthoscopics are so-named for having zero or almost zero distortion, though the field of view is necessarily limited as a result.

While Mental posted one way to make a simple cross-hair using optical fibre, there are other ways, for example printing a grid onto transparency film and sandwiching that between glass cut from microscope slides; should work OK with some of the modern high DPI laser printers.

Another way if you have access to a CNC machine and a drill press is:
- coat a glass microscope slide in beeswax, then
- using the CNC machine to scribe a grid in the wax.
- apply a "witches brew" of acid to etch the grid into the glass.
- cut the reticle as a disc out of the slide using the drill press spinning a metal cylinder and abrasive,
- remove the wax, and
- mount the reticle at the focal plane of an eyepiece.