Magnification Limitation for Optical Microscope

LARRY R CORRIA

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Nov 11, 1996, 3:00:00 AM11/11/96

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I was curious as to the approximate magnification limit of a standard
light microscope. For the sake of argument I'll say using green light.

Daniel P. B. Smith

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Nov 11, 1996, 3:00:00 AM11/11/96

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In article <5669f6$4...@sjx-ixn3.ix.netcom.com>,

LARRY R CORRIA <lar...@ix.netcom.com> wrote:
>I was curious as to the approximate magnification limit of a standard
>light microscope. For the sake of argument I'll say using green light.

This is another one of these "your-mileage-may-vary" questions because
there's no well-defined point at which the magnification becomes "empty."
And so much depends on what you want to do. For example, if you just want
to identify and detect the presence of something really tiny, with
darkfield illumination or something like that, it may be appropriate
to goose the magnification up beyond normal limits--because a big, blurred
image may be more appropriate for SOME purposes than a small, sharp one.

(Actually detection is completely different from resolution. You can
easily see a single strand of a spiderweb from several feet away
when the sunlight hits it just right... figure out what THAT is in
minutes of arc and how it relates to the diffractional-limited resolution
of the eye.)

Using a first-rate professional research microscope, appropriately
prepared sections, an oil immersion object _AND properly matched
oil immersion condenser,_ 1000X is a nice, round number that's not
wildly out of sync with reality.

Believe it or not, I was once in a situation where I was able to see
for myself that the results were not quite what they should be--and
the reason turned out to be that the lab was using some kind of
"standard" cover slip and the particular objective required a
special cover slip of somewhat different thickness...

Using my second-hand $40 1920's vintage microscope, with no proper
illuminator, no oil immersion, etc. 250X might be more like it.

--
Daniel P. B. Smith
dpbs...@world.std.com

Steve McGrew

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Nov 11, 1996, 3:00:00 AM11/11/96

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In article <5669f6$4...@sjx-ixn3.ix.netcom.com>, lar...@ix.netcom.com(LARRY R CORRIA) wrote:
>I was curious as to the approximate magnification limit of a standard
>light microscope. For the sake of argument I'll say using green light.

Oops. A half wavelength/refractive index is the resolution limit, which I
assume you mean. You can magnify all you want; you just won't resolve details
beyond the resolution limit.

Steve McGrew

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Nov 11, 1996, 3:00:00 AM11/11/96

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In article <5669f6$4...@sjx-ixn3.ix.netcom.com>, lar...@ix.netcom.com(LARRY R CORRIA) wrote:
>I was curious as to the approximate magnification limit of a standard
>light microscope. For the sake of argument I'll say using green light.

Roughly half a wavelength, divided by the refractive index of the medium the
sample is in (usually about 1.5).

peter...@aol.com

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Nov 14, 1996, 3:00:00 AM11/14/96

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I believe that the practical magnification limit for optical microscopes
(using immersion optics) is about 1200X.

jgr...@globaldialog.com

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Nov 18, 1996, 3:00:00 AM11/18/96

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In article <5669f6$4...@sjx-ixn3.ix.netcom.com>,
lar...@ix.netcom.com(LARRY R CORRIA) wrote:
>
> I was curious as to the approximate magnification limit of a standard
> light microscope. For the sake of argument I'll say using green light.
>

Hi, Using the top of the line 100x/1.3 n.a., oil immersion and green light you
should be able to resolve (theoritcally) between 0.5 and 0.25 microns. Blue
light will give you a bit more resolution. And if you carry this thing to lower
wavelengths, say UV (and there was just a scope developed by Zeiss before the advent of
EMs) you had much more resolution. Of course no one could see UV for the obvious
reasons (Blindness, Cataracts, etc.) unless one had many grad students ready and
eager to learn the mysteries of Hi-Res Microscopy. (joke) So they used a
phosphorous screen for observation.

Jeff at: www.jhmicro.com
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