Features of an Objective Lens

01:00:13.02 the nomenclature on an objective lens
01:00:15.25 and cover what some of the properties
01:00:17.27 are and what information is
01:00:19.14 printed on the front of that lens.
01:00:21.20 So, the objective lens,
01:00:23.24 as we've talked about before
01:00:25.05 is really the most important part
01:00:27.04 of the optical system.
01:00:28.08 Also one of the more expensive parts
01:00:30.12 of an optical system.
01:00:32.13 The information on the lens,
01:00:33.27 on the top you can see the manufacturer,
01:00:36.21 it'll tell you the aberration correction
01:00:39.13 for example, here it says "Plan Apo,"
01:00:41.29 and that stands for "Plan" flatfield correction,
01:00:46.16 and "Apo" standing for apochromatic correction,
01:00:50.02 so a very broad range of wavelengths
01:00:52.19 from the violet to the red.
01:00:53.24 Okay, the magnification,
01:00:56.18 which is shown here as 60x
01:00:58.25 is printed, as well as the color code,
01:01:02.06 in our case, blue, for 60x lenses.
01:01:05.24 So all 60x lenses are going to have
01:01:08.05 a blue band around them.
01:01:09.12 And then it shows you a slash, and a 0.95,
01:01:15.14 that's the numerical aperture of the lens.
01:01:17.22 The light gathering capability
01:01:20.13 and the resolution capability of that lens.
01:01:23.21 Then below that,
01:01:25.17 you have specialized optical properties,
01:01:27.22 in this case, it says "DIC M,"
01:01:30.00 that means that this lens is
01:01:32.05 of sufficient quality and low strain
01:01:34.20 that it can be used for
01:01:35.18 the technique of differential interference contrast.
01:01:37.26 Similarly, if you had a lens
01:01:40.26 that was good for phase contrast,
01:01:43.03 and had a phase ring in it,
01:01:44.14 it would tell you that,
01:01:45.13 it would have a "Ph" for phase on it.
01:01:48.18 "M" designates that this is a medium
01:01:52.15 numerical aperture lens,
01:01:55.18 different manufacturers have different nomenclature
01:01:58.05 for their types of DIC.
01:02:00.20 And that basically tells you which prism
01:02:02.26 in the microscope to match with that lens
01:02:05.08 to get differential interference contrast to work.
01:02:08.02 Below that, will show you the tube length,
01:02:11.15 and most, as you can see that right here.
01:02:14.14 The tube length focal length,
01:02:16.01 now most microscopes nowadays
01:02:18.20 are infinity corrected, and that's why
01:02:20.21 you see the infinity symbol there on that bottom line.
01:02:23.10 /0.11-0.25, which is the cover glass
01:02:30.05 thickness that that lens can work with.
01:02:33.05 In older microscopes, finite microscopes,
01:02:36.28 it would give you a focal length
01:02:38.24 to the tube lens,
01:02:39.22 such as, say 160 or 200 / 0.11.
01:02:46.02 So the working distance is then shown here
01:02:50.28 as "WD," and the working distance is
01:02:55.01 the actual free working distance
01:02:58.18 not including the coverslip
01:03:00.11 that you can focus into the specimen.
01:03:02.12 So working distance in the case here,
01:03:05.20 .13, shown here in millimeters,
01:03:10.17 a 130 microns that you can then focus
01:03:13.27 beyond the coverslip into the specimen.
01:03:16.03 So the important point there is to
01:03:18.02 know that that already is taking into account
01:03:20.25 the coverslip and that's how far
01:03:22.20 you can focus into the specimen
01:03:24.27 on the other side of your cover glass.
01:03:26.22 The cover glass thickness range
01:03:30.21 is important and you need to adjust
01:03:34.08 the correction collar to correct for
01:03:36.04 spherical aberration, due to the
01:03:38.28 variability in the cover glass thickness.
01:03:41.09 And then you have sort of this cone here
01:03:44.22 with the front element in it.
01:03:46.29 Often times if it's an oil immersion lens
01:03:49.15 or an immersion lens
01:03:50.07 with short working distance,
01:03:51.14 that will retract with a spring.
01:03:53.17 And the mounting thread here, generally in brass.
01:03:58.14 And I think those are pretty much
01:04:00.19 the key points that you can get from
01:04:02.23 reading the front of an objective lens.
01:04:05.13 There are many many different categories
01:04:07.02 of lenses, and every manufacturer though,
01:04:11.04 will have this sort of standard information.
01:04:14.08 Thank you.

This Talk

Speaker: Steve Ross

Audience:

Researcher

Recorded: March 2012

Talk Overview

Steve Ross explains the features of an objective lens and what all of those markings actually mean.

Speaker Bio

Steve Ross

Stephen Ross is the General Manager of Product and Marketing at Nikon Instruments. He is also very involved in teaching microscopy at the Marine Biological Laboratory in Woods Hole and at the Bangalore Microscopy Course at the National Centre for Biological Sciences. Continue Reading

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