Cover Glass Correction Using an Adjustable Objective
Read the Edited Video Transcript for ‘Cover Glass Correction Using an Adjustable Objective’
Hey, this is Chad with Munday Scientific. Today we’ve got an Olympus BX41 here with an S Plan Apo 40X objective, and we’re going to talk about coverglass correction collars.
We get a lot of questions about these, so let’s take a closer look at how they work and why they’re important.
What Is a Coverglass Correction Collar?
If you look closely at this objective, you’ll see several numbers on the correction collar representing different coverglass thicknesses.
There’s also a small white scribe mark that shows you where the collar is currently set.
For most applications, you’re going to want that mark set at approximately 0.17 mm. That’s because 0.17 mm is the standard coverglass thickness that you’ll commonly encounter on prepared microscope slides.
However, there’s a reason this collar is adjustable.
Depending on the actual thickness of the coverglass you’re viewing through, the image may look better at a slightly different correction setting. The purpose of the collar is to allow you to compensate for those differences and achieve the best possible image.
What Is the Coverglass?
If you’re not familiar with the terminology, the coverglass, or coverslip, is the thin piece of glass placed over the specimen on the microscope slide.
You can see that this particular slide has a coverslip over the tissue. It’s extremely thin and sits nearly flush with the surface of the slide.
Because you’re viewing the specimen through this glass, variations in its thickness can affect the optical performance of a high-quality objective.
Why the Correction Collar Needs to Move Freely
It’s important that the correction collar on the objective moves properly.
If an objective sits unused for a long period of time, the collar can sometimes become stuck in one position. These can be very difficult to free up without damaging the objective.
If the correction collar is seized, you’ll generally want to have a microscope service professional repair the objective rather than trying to force it.
For this demonstration, we’re going to set the correction collar to 0.17 mm, since that’s the typical coverslip thickness we’re working with.
Installing and Testing the Objective
Now we’re going to install the objective on the microscope and see how the image looks.
We’ll start by locating the specimen at lower magnification and bringing it into focus.
Since we have the 2X objective in place initially, we’ll flip the condenser’s top element out as needed for the low-magnification objective.
Then we’ll move to the 10X objective, bring the specimen into focus, and set Köhler illumination.
We’ll make sure the condenser is properly centered and that the eyepieces are set correctly.
From there, we’ll move through the 20X objective and then up to the higher-magnification objectives.
Checking the 40X Image
Now we’ll move to the 40X objective with the coverglass correction collar that we just set.
And that’s a beautiful image.
In this case, setting the correction collar to 0.17 mm gave us an excellent result.
The important thing to understand is that the ideal setting can vary depending on the thickness of the coverslip. If the image isn’t as sharp as you expect, adjusting the correction collar slightly may improve it.
Use the Nosepiece to Change Objectives
There’s another important point about objectives with correction collars.
Some pathologists and other microscope users like to change objectives by grabbing the objective itself and rotating the nosepiece.
That’s not a good habit when you’re using an objective with a freely moving correction collar.
If the collar is properly lubricated and operating as it should, grabbing the objective can accidentally rotate the correction collar. That changes your setting and can affect image quality, forcing you to continually readjust or refocus the microscope.
Instead, rotate the microscope using the nosepiece itself rather than grabbing the objective.
Periodically check the correction collar as well and make sure it’s still set where you want it—typically around 0.17 mm for a standard coverslip.
Questions or Microscope Equipment
If you have any questions about coverglass correction collars, microscope objectives, or microscope setup, you can always email us at .
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