emersion oil

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Judge
Posts: 95
Joined: Sat Dec 18, 2021 2:36 pm

emersion oil

#1 Post by Judge » Wed Jan 18, 2023 9:25 pm

I just looked at an oil emersion video. It suggested placing the oil on the condenser lens in addition to the cover slip. I’ve never heard of that. Any opinion?

apochronaut
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Joined: Fri May 15, 2015 12:15 am

Re: emersion oil

#2 Post by apochronaut » Thu Jan 19, 2023 1:54 am

That is normal.
Any microscope optic that has an N.A. specification higher than 1.0 requires a specific grade of immersion liquid to achieve that specification, which will be designated in the optic's specifications. Mostly those are condensers and objectives. Immersion in air can achieve an N.A. of 1.0 maximum and in practice less, so .95 is considered the upper limit.
Normal and common immersion liquids and their N.A. limit are water N.A. 1.33, Glycerin ( also soluble in water , so easy clean) N.A. 1.47 and Immersion oIl N.A. about 1.52 but oils can differ a bit. Just about any optically clear liquid can be used for immersion, as long as the immersed optic is corrected for it. N.A.s of 1.7 can be achieved with certain immersion liquids, such as methyl iodide.

Condensers are a bit simpler and are typically used dry and at a sub 1.0 N.A. unless the chosen objective has an N.A. higher than 1.0. Oiling an oil immersion condenser will help a higher N.A. immersion objective achieve it's theoretical maximum resolution.

Using a dry sub 1.0 N.A. condenser with an immersion objective causes the objective's N.A. specification to be reduced to a value median between the two. A 1.25 N.A. objective for instance, used with a .95 N.A. simple condenser such as an abbe will work at about 1.13 on axis. Off axis the N.A. will decline quite dramatically in an abbe condenser but dry condensers with superior correction, such as aspheric or aplanatic will maintain their rated N.A. laterally as well.

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