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How to Clean Objective Lenses and Filters

00:00:11.04 So today I'm going to talk about how to clean microscope
00:00:13.21 optics, and in particular, how to clean objectives and
00:00:17.17 optical filters. And this is something that is an important
00:00:21.15 technique to know because it's pretty easy to get optics
00:00:24.00 dirty. Particularly if you're using oil immersion objectives,
00:00:28.00 as you tend to accumulate old oil on the objectives, you can also
00:00:30.23 smear oil on air objectives that aren't supposed to have oil on them.
00:00:33.10 Those are probably the two major sources of dirt that we
00:00:36.14 see here. Before you go to clean your objectives, it's best to
00:00:41.01 check the manufacturer's recommendations. Different manufacturers
00:00:44.13 recommend different methods of cleaning their objectives.
00:00:47.09 In particular, different solvents or cleaning products to use.
00:00:51.02 So what I'm going to recommend here, what we like to use
00:00:53.21 for our Nikon objectives, but if you have a different microscope
00:00:56.26 you may want to be using some other cleaning product.
00:00:59.01 So the first thing to do is to inspect your objectives and
00:01:04.01 see if they need cleaning. So we can take off an objective
00:01:06.13 from the scope here. And then take a look at it. And the first
00:01:12.19 step is just to inspect it by eye, you can look at it and see
00:01:16.06 if it looks like it's dirty. You can look through it, to see if
00:01:19.08 you get a good clear image through it. It's hard to do this
00:01:22.09 with these high magnification objectives, but for low
00:01:24.10 mag objectives, looking through them is an easy way to spot
00:01:27.06 dirt. And then for these high mag objectives which have these
00:01:30.09 small lenses, one useful technique is that you can pull off
00:01:34.01 the eyepiece of the microscope. And if you look through
00:01:36.21 them backwards, they make a very good magnifying glass, so you
00:01:39.02 can use that then to get a close up inspection of the front element
00:01:43.02 of this objective, and see if it's got oil or dirt or debris on it.
00:01:46.26 So to clean this, I'm going to put it down on the table,
00:01:51.02 get a piece of lens paper here, and then peel off a single sheet
00:01:56.26 of lens paper, being careful to only handle it by the edges,
00:01:59.00 not by the center because I don't want to get fingerprints
00:02:00.27 and oil from my fingers onto the objective.
00:02:03.01 So you take your lens paper, handling it by the edges, and then
00:02:06.04 the way I like to clean objectives, these Nikon objectives, is using
00:02:10.02 xylene or chloroform to remove the oil, followed by methanol
00:02:13.19 for cleaning up any residue left behind by those solvents.
00:02:17.25 And in all cases, I use the spectrophotometric grade
00:02:20.17 solvents. So to clean this, you put the lens paper down on
00:02:24.00 the objective, take your solvent here, and then put a single
00:02:27.16 drop on the objective, and then pull the lens paper gently
00:02:32.09 from side to side, so that you wick off the solvent, along with
00:02:35.04 any dirt on the objective. You can take a look at it in between
00:02:39.23 and see that this is now much cleaner. And then I'll just repeat
00:02:43.29 with methanol. And that's how you clean an objective.
00:02:53.05 For objectives like this air lens here, where the front element
00:02:57.16 is recessed, the lens paper trick doesn't work so well
00:03:00.19 because it doesn't get into the concave part of the lens.
00:03:02.25 And so for those, I like to use cotton swabs, you can either buy
00:03:06.25 commercial cotton swabs, the glue-free ones are best.
00:03:09.14 Or you can make your own just by taking pure cotton and twirling
00:03:12.17 a little wooden stick in it to pick it up. But otherwise the cleaning
00:03:16.18 procedure is the same, we're just going to use a swab instead
00:03:18.22 of lens paper. So again, I'll wet my swab with solvent
00:03:22.17 and then just go in here and gently swipe across the surface
00:03:28.04 of the lens, using a new surface of the cotton swab each time.
00:03:30.26 And again, I would repeat with methanol to remove any residue
00:03:35.00 from the xylene, until that objective is clean.
00:03:37.12 For air objectives, if they don't have oil on them
00:03:43.09 you also want to use a blower on them to remove any loose dust
00:03:46.06 so that you don't scratch the objective. If the objective
00:03:48.18 is oily, this is not terribly helpful because the oil will stick
00:03:51.29 the dust in place. But if it's not, it's generally a good practice
00:03:55.28 to use a blower like this one to blow off any loose dust on
00:03:59.08 the surface of the objective. Another useful way of detecting
00:04:04.15 these, in addition to looking at them with a magnifier
00:04:08.11 is also you can look through the objective at a distant object
00:04:14.09 and see if there's blur or dirt, which you can see if the streaks
00:04:18.22 or aberrations in the image. That works better for low magnification
00:04:22.20 objectives, than high magnification ones. So that's the basics
00:04:27.03 of cleaning objectives, it's good practice to do this routinely.
00:04:31.16 Particularly for oil objectives, which tend to build up residue
00:04:34.04 and gunk. One other point worth bearing in mind is that
00:04:38.17 these solvents that we're using here are really designed
00:04:40.07 for removing oil from objectives. If your objective has
00:04:43.12 been dirtied with say, tissue culture media or some other
00:04:46.15 water-based substance, then you'll want to use water,
00:04:49.18 maybe with a little bit of soap in it to remove that residue
00:04:52.12 and then follow up with distilled water and methanol,
00:04:55.14 probably to get the cleanest lens. Some manufacturers also
00:04:59.23 recommend using Sparkle window cleaner, or they have custom
00:05:03.02 cleaning products you can use for their objectives.
00:05:06.19 So now I want to talk about cleaning the filters and we're
00:05:10.26 going to talk about cleaning two different kinds of filters.
00:05:12.26 So here we have a filter that's mounted, you can see it's mounted
00:05:19.16 with this black ring. And we'll want to clean this slightly differently
00:05:23.00 than an unmounted filter. So let me get a piece of lens paper to put
00:05:26.24 these on. So again, we use lens paper here to avoid
00:05:31.07 getting dirty. So there's a mounted filter, which is mounted
00:05:35.05 in this metal ring. Here's an unmounted filter now, which
00:05:38.04 doesn't have that ring around it. It's just a piece of glass.
00:05:40.04 This, you want to be especially careful because putting it
00:05:43.05 down, there's no metal ring for it to rest on.
00:05:45.06 For the unmounted filter here, we can use the same lens paper
00:05:51.16 trick we used for the objective. First, I want to blow it off
00:05:57.03 and remove any loose dust here. So clean off the dust,
00:06:02.14 and now we'll take a piece of lens paper, again handling
00:06:08.08 by the edges. And then, use a little stick here and put a drop
00:06:15.10 of solvent on the optic. And then again, do this drag mopping
00:06:22.29 technique to gently drag the solvent off, pulling any dirt
00:06:26.23 with it. And the stick is here just to keep the lens, or the uh
00:06:30.01 filter from sliding around as I do that. That technique does not
00:06:34.24 work on these mounted filters because you can't get
00:06:38.17 the lens paper in close contact with the filter everywhere.
00:06:42.04 So here again, we're going to use cotton swabs. Again,
00:06:46.07 blow off any dust so we don't scratch it with dust on it.
00:06:48.24 Then, put it down on our lens paper. Take a clean swab,
00:06:53.11 you always want to use a clean cotton swab, so you don't
00:06:55.17 transfer dirt from one optic to another. Moisten it with solvent,
00:07:02.04 and then gently, using a spiral motion, clean it from the center
00:07:07.10 to the outside. Just removing any residue or dirt on there.
00:07:11.20 And that's how you clean a filter.

This Talk
Speaker: Kurt Thorn
Audience:
  • Researcher
Recorded: April 2012
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Talk Overview

It is important to know how to clean objective lenses because dirt and residue on the surface of objective lenses and filters can degrade image quality. This tip describes how to inspect lenses and filters for dirt and how to clean them properly with solvent so that these expensive components will not be damaged in the process.

Speaker Bio

Kurt Thorn

Kurt Thorn

Kurt Thorn is an Assistant Professor of Biochemistry and Biophysics at UCSF and Director of the Nikon Imaging Center – a facility that provides cutting edge light microscopy equipment to UCSF researchers. Kurt can be followed on his blog at http://nic.ucsf.edu/blog/. Continue Reading

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