Re: magnification of 250

On Aug 20, 12:09 pm, "helio" <forbid...@xxxxxxxxx> wrote:
"Kevin Cunningham" <sms...@xxxxxxxxxxxxxx> wrote in message

news:e810940d-7653-4d75-8e26-46d3dcc7e1b0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Aug 19, 6:54 pm, "helio" <forbid...@xxxxxxxxx> wrote:





"Fred" <mb...@xxxxxxxxxxx> wrote in message

news:20f318a1-26e9-46db-b339-0a0a548e08b1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

To follow up on what Heini was saying. The resolution of the human
eye is about 0.2 mm, give or take a few tenths. A 1000x magnification
gets you to 0.2 micrometers. The resolution of the microscope,
limited by diffraction of light, is a bit more than 0.2 micrometers.
So magnifications above 1000x are useless, empty magnification, except
for specialized cases as outlined by Kevin Cunningham. As he
emphasized, the Numerical Aperture of a microscope objective
determines resolution, not the magnification.

Now I understand what heini was saying about 1000X magnification, thanks.
And I imagine that is not easy for physicists to cheat the laws of
diffraction :)
Helios,
There is a rule of thumb that a lot of people use, never have more
than 1000 times the NA as magnification.  There is a limit at around
1.4 - 1.45 NA if you are using conventional immersion media so you
shouldn't have more than 1,400 power.

Kevin,

This is a goldthumb rule to me. So, is a 1400 magnification  in the order of
the feasible things? This is the first time I have the sureness about a
dream of mine. One of the main goals of my observations is to identify
bacteria, whose details (presence of flagella, helical structure) are very
hard, if not impossible, to discern at 100X.

Some powers are just popular, 40X for instance.  If you tried to sell
a bio objective that was 60X rather than 40X you would have some
problems, every one selling 60X objectives sells 40X objectives.
Popularity is the primary reason why some powers are sold and some
aren't.  For instance the NC 40X isn't popular even though it's
necessary.  See any hematology dept.

I googled and found that NC means No Coverglass. Suddenly, I feel that a NC
40X is necessary to me too :)

Making an objective has a lot to do with making one that will sell to
users

I see, as well as making many other things.

Heini,

The real point is once again, NA. If you have a high NA objective, an
oil condenser and you will actually oil the condenser then you can
look for objects in the 0.25 - 0.15 micron range. If not, you have
problems.

The less you think of mag and the more you consider NA the better off
you will be.

Thanks,

Kevin Cunningham
SMS
.

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