the nomenclature on an objective lens
and cover what some of the properties
are and what information is
printed on the front of that lens.
So, the objective lens,
as we've talked about before
is really the most important part
of the optical system.
Also one of the more expensive parts
of an optical system.
The information on the lens,
on the top you can see the manufacturer,
it'll tell you the aberration correction
for example, here it says "Plan Apo,"
and that stands for "Plan" flatfield correction,
and "Apo" standing for apochromatic correction,
so a very broad range of wavelengths
from the violet to the red.
Okay, the magnification,
which is shown here as 60x
is printed, as well as the color code,
in our case, blue, for 60x lenses.
So all 60x lenses are going to have
a blue band around them.
And then it shows you a slash, and a 0.95,
that's the numerical aperture of the lens.
The light gathering capability
and the resolution capability of that lens.
Then below that,
you have specialized optical properties,
in this case, it says "DIC M,"
that means that this lens is
of sufficient quality and low strain
that it can be used for
the technique of differential interference contrast.
Similarly, if you had a lens
that was good for phase contrast,
and had a phase ring in it,
it would tell you that,
it would have a "Ph" for phase on it.
"M" designates that this is a medium
numerical aperture lens,
different manufacturers have different nomenclature
for their types of DIC.
And that basically tells you which prism
in the microscope to match with that lens
to get differential interference contrast to work.
Below that, will show you the tube length,
and most, as you can see that right here.
The tube length focal length,
now most microscopes nowadays
are infinity corrected, and that's why
you see the infinity symbol there on that bottom line.
/0.11-0.25, which is the cover glass
thickness that that lens can work with.
In older microscopes, finite microscopes,
it would give you a focal length
to the tube lens,
such as, say 160 or 200 / 0.11.
So the working distance is then shown here
as "WD," and the working distance is
the actual free working distance
not including the coverslip
that you can focus into the specimen.
So working distance in the case here,
.13, shown here in millimeters,
a 130 microns that you can then focus
beyond the coverslip into the specimen.
So the important point there is to
know that that already is taking into account
the coverslip and that's how far
you can focus into the specimen
on the other side of your cover glass.
The cover glass thickness range
is important and you need to adjust
the correction collar to correct for
spherical aberration, due to the
variability in the cover glass thickness.
And then you have sort of this cone here
with the front element in it.
Often times if it's an oil immersion lens
or an immersion lens
with short working distance,
that will retract with a spring.
And the mounting thread here, generally in brass.
And I think those are pretty much
the key points that you can get from
reading the front of an objective lens.
There are many many different categories
of lenses, and every manufacturer though,
will have this sort of standard information.
Thank you.