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... Re: [OM] Why is the 50mm the brightest lens? #2

Subject: ... Re: [OM] Why is the 50mm the brightest lens? #2
From: DBellamy2k@xxxxxxx
Date: Sat, 11 Aug 2001 17:57:24 EDT
... 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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