If you’re not sure what the objective is or what it does please check out Microscope Objective: The Eyes of the Microscope. In this article we will explore all the detail and nuance associated with integral part of the microscope.

Sphericalaberration correction

Figure 2 shows an aspherical lens and a thin plate. Spherical aberration of the aspherical lens is corrected based on a use of a thin glass plate. All the light rays at different radial distances from the lens center focus at the same location when a thin glass plate is used. When replacing the thin glass plate with a thick glass plate, the marginal rays focus further to the lens than the rays close to the optical axis of the lens.

The microscope nosepiece, also known as the revolving turret, sits below the head of the microscope and locks the objective lens into position over the stage aperture by rotating in either direction. The microscope nosepiece can house anywhere from 3 to 5 objectives depending on the type of microscope.

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Sphericalaberration in mirrors

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Spherical aberration correction is important for all high-performance systems. A vision system or imaging system with uncorrected spherical aberration cannot produce a high-resolution image. When designing an optical system, designers must consider all the optical components including windows in the system and minimize spherical aberration and other aberrations including chromatic aberration.

The revolving nosepiece is located at bottom of the head of a microscope on an upright microscope. The nosepiece is easily identifiable because it has a distinct disc shape and it will have the objective lenses screwed into it.

Sphericalaberration and chromatic aberration

The revolving nosepiece revolves by grasping the objective along the etched grip section of the objective lens and rotating it either clockwise or counterclockwise depending on which objective you are trying to lock into position. Some larger microscopes have etched grip right on the revolving nosepiece so if the microscope you are using has the grip there you should use that to turn the nosepiece.

The presence of spherical aberration results in a lens that cannot bring all light rays into the same focus. An imaging lens with a large amount of spherical aberration cannot form a good image at a large aperture but may get sharper images at smaller apertures.

Sphericalaberration example

The revolving nosepiece was patented in 1928 and in the patent application appealed to the time saving nature of the invention. You can see below that nosepiece of today has changed a little from the original design, but the basics are essentially the same.

The main purpose of the revolving nosepiece of the microscope is to easily and systematically interchange the objective lenses. Objective lenses come in increasing magnifications and depending on the microscope, the nosepiece can hold anywhere from 3 to 5 objectives.

Most objective lenses are corrected for a thin cover glass and camera lenses are corrected for a thin sensor window. It is important to keep this in mind to avoid unintentional introduction of spherical aberrations when using off-the-shelf lenses for high-resolution imaging applications.

A simple lens with undercorrected spherical aberration or negative spherical aberration forms an image of a point object which is usually a bright dot surrounded by a halo of light. Figure 1 is a sketch of a spherical singlet lens with a spherical surface which produces negative spherical aberration. The spherical aberration causes that the focal location changes with the light ray height. The rays close to the optical axis or lens center focus (intersect the axis) near paraxial focus position. As the ray height increases, the position of the ray intersection with the optical axis move further and further from the paraxial focus. The marginal rays focus closer to the lens than the paraxial rays.

There are times where I have found that my nosepiece has become loose and the rotating mechanism is not rotating in a controlled manner. If you find that you are experiencing this problem one thing to check is the nosepiece screw. If it’s too tight you can loosen a bit or if it’s too loose, which is normally the case, you can tighten it.

On an inverted microscope the nosepiece is located underneath the stage with the objectives pointed upward. The nosepiece on an inverted microscope works the same way as a standard microscope.

Sphericalaberration photography

Sphericalaberration in a lens

The revolving nosepiece is a time saving and integral part to the working of a microscope. The nosepiece enables the microscope user to quickly change objective lens magnifications and while keeping the specimen centered. I hope this article has cleared up any ambiguity you may have had on this topic and now you’re ready to lock n’ load and start magnifying!

There are many reasons you would want to remove your objective lenses from the nosepiece but the most common is removing an objective to clean it. To remove an objective, you just twist the objective to the left just like a screw and unscrew it with your hand.

What issphericalaberration in Physics

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Sphericalaberration formula

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Sophisticated microscope nosepieces lock the objective lens into place which such precision that the objective stays in alignment and completely centered with the with the specimen. This precision eliminates the need to re-position a slide and reduces the time to focus.

Spherical aberration is one of the most common types of optical aberrations and can be defined as the variation of focus position with light ray height or distance from optical axis. Ideally, an aberration-free lens direct all light rays to a common focal point for a focusing lens or produce a perfect image for an imaging system. Spherical aberration presented in an optical system affects the image clarity or focus spot size.

Spherical aberration can be introduced into an optical system when the lens is not designed to properly correct the spherical aberration or a lens is not working under the ideal or designed conditions such as window glass thickness changed, immersion medium changed, etc.

Before you begin using the microscope, ensure the lowest power objective is locked into place by listening for the auditory click sound. Once you find focus with a low power objective the next step is to rotate the nosepiece to the higher power objective. Then once you find focus again you will rotate the nosepiece again to the higher power objective and repeat this process until you reach the desired magnification.

If you’ve ever seen or used a revolver you know the cylinder contains the bullets which are lined up with the barrel and fired by the firing pin. In any action movie with a revolver you see the person spinning the cylinder and locking it into place in preparation for firing the gun. The nosepiece plays a similar role for the microscope.

To put the objective back, it is sometimes easier to twist the objective left to find the threading and then begin twisting the objective lens to the left. Below is a demonstration that illustrates this.

Brandon is an enthusiast, hobbyist, and amateur in the world of microscopy. His love for science and all things microscopic moves him to share everything he knows about microscopy and microbiology.