Re Eung-Gi,s /Edmunds Optic Mirage

[edsap@xxxxxxxxxxxxxxxxx (Peter Homer)]

I have examined my optic mirage device and can answer some of Eung-Gi,s
questions which I was not able to before. I think it must be the same as
Edmunds as it is made/suplied by an American firm Opti-Gone Box 8118 Van
Nuys, CA 91409 USA . Perhaps they may be cheaper direct from them and maybe
they hav e other sizes. The American patent number is 3647234 I think the
image is real or it would not appear above the dome Edmunds advert even
says that it can be photographed.
 I dont know the original inventor but in 1851 Wenham described a dark
ground condenser for microscopes. Which consisted of a single truncated
hollow silvered parabolic reflector . A meniscus lens was fitted to the top
below the focus to correct for the slide thickness but this may have been a
later addition .Someone called shadbolt who invented another type realised
that his had shortcomings and suggested an improvement by constructing
Wenhams in glass . Wenham took the idea up and produced Wenhams parabaloid
which became the most popular dark ground illuminator ever made (to quote
an old textbook). This did not require silvering as there was total
internal reflection from the sides . In 1856 Wenham produced another
version for use with high power objectives which dispensed with the
meniscus and had a flat top which was in oil contact with the bottom of the
slide.  Dark ground microscopy fell out of favour for a while but in 1907
Wenhams parabaloid was revived and iI think is still available today
although better illuminators have been produced since.
 From what others in the group say even Edmunds version seems to have been
around for some time and I do remember seing one in a different cataloge
some time before the one I bought. I also have a book on holography which
refers to them because they have been confused with holograms also a
Russian scientist who produced a moving projected holographic image used
parabolic reflectors to do so .
                                                        P.J.Homer




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