... 2. Tim Hughes then wrote:
<< far as fast glass under F1.0 is concerned, microscopes objectives often
achieve numbers well under 1.0 ( as low as F 0.5? I think) when they use oil
immersion objectives. The immersion objective gives a much larger relative
refractive index between the glass and the oil. >>
I have certainly heard of F 0.6 microscope objectives with oil immersion.
But with your Olympus OMs, this means that you will have to cover your
subject and your front lens element in oil (boiling or otherwise) by having
them both immersed in it.
I can't remember if the oil is designed to have the same refractive index as
the objective glass, (a near to 1.00 ratio between the objective and the
glass I think).
I remember distantly at University using different refractive index oils to
find the refractive index of unidentified crystals using a thing called the
Becke Line Test. So they are available. Fun if you have to do it only once.
Of course, if you dunk the crystals into oil of exactly the same refractive
index, basically they disppear!
Of course, if you have a set of these refractive index labelled bottled oils,
and pour the high r.i. oil back into the low r.i. bottle when you have
finished, you cock up the entire experiment for the next poor unsuspecting
student.
Dave Bellamy.
http://members.aol.com/synthchap/
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