Microscopes are complex instruments that use multiple components to produce enlarged pictures of the specimens. They use different types of lenses to magnify the image and view them on the eyepiece or monitor. Microscopes of all types, including optical and electron, use objectives and condenser lenses to give you the observation. However, light and simple microscopes do not use the same lenses. So, what do condenser and objective lenses exactly do?
This article brings you everything you need to know about condensers and objective lenses.
Table of Contents
What is a Condenser Lens?
The condenser lens is the first lens that comes in contact with the light source during microscopic observation. Optical microscopes use condenser lenses that help converge the light from the light source, while electron microscopes converge the electron beam into a thin one.
Condenser Lens in Optical Microscopes
In optical microscopes, a condenser or condenser lens refers to the glass lens below the stage and above the light source. It gathers the light from the illumination source and converges into a light cone. This light falls onto the specimen to illuminate it for observation.
Condenser lenses in optical microscopes are of three types:
- Abbe Condensers: Abbe condensers do not have any spherical or chromatic correction.
- Aplanat Condensers: These condensers are corrected only spherically.
- Aplanat-Achromat Condensers: They are both chromatically and spherically corrected. The chromatic correction includes blue and red longitudinal chromatic corrections.
The aplanat-achromatic condensers are widely used for bright field photomicrography, while the abbe condensers come into use during observational work. Abbe condensers are more precise and moveable but also more expensive.
Condenser Lens in Electron Microscopes
The condenser lens in an electron microscope performs the same function of converging rays from the illumination source as in an optical microscope. However, the condenser lens in an electron microscope is not made of glass. Instead, it is an electromagnetic lens that produces an electromagnetic field. The condenser lens in electron microscopes converges the beam of electrons and defines the size of the beam from the electron gun.
What is an Objective Lens?
Objective lenses are the main system in a microscope that enables the magnification of an object. The objective lens also performs the same function in light compound and electron microscopes but in unique ways.
Objective Lens in Optical Microscope
Objective lenses are one of the most critical elements of optical microscopes as they produce magnified images. They are attached to the rotatable nosepiece of the microscope. Objective lenses for optical microscopes come in various magnification choices and types, including spring and oil immersion lenses. You can choose and switch between different objective lens magnifications by rotating the nosepiece.
When the light falls on the specimen from the lower side, the objective lens magnifies the sample according to the lens magnification and resolution. The eyepieces increase the overall magnification of the observation.
Different objective lenses in optical microscopes include:
- 100x (Spring)
- 400x (Spring, oil immersion)
You can estimate the lens magnification by the lens’s size. Usually, the lowest magnification objective lens is the smallest. High-quality DIN standard objective lenses are also color-coded and interchangeable.
Objective Lens in Electron Microscope
The objective lens in an electron microscope is also an electromagnetic lens that absorbs the beam of electrons coming from the condenser lens. These lenses comprise metal wire coils inside pole pieces that generate magnetic fields. The magnetic field controls the electrons’ path resulting from changes in the applied current. The objective aperture enhances the specimen contrast.
The final image is on a phosphorescent screen or captured through a computer digitizing and archiving (CCD) camera for observation.
Condenser-Objective (C-O) Lens
The condenser-objective lens, or C-O lens, is used in electron microscopes as a dual lens. It produces magnetic fields that act as a condenser and objective lens subsequently. The C-O lens uses the pre-magnetic field as a condenser, while the post-magnetic field is the objective lens. The pre-magnetic field converges the electrons into a thin beam, and the post-magnetic field enables it to produce an image of the specimen.
While the C-O lens acts as two lenses at one time, it has only one peak of the magnetic field. The dual nature of the lens results from the strong magnetic field. The pre-magnetic field converges the electron beam while the lens demagnifies the electron beam; this demagnification helps produce a high-resolution image. The post-magnetic field enlarges the image for observation, giving you high-magnification imaging.
The Bottom Line
The main difference between the condenser and objective lens is their unique functions in microscopes. The condenser lens helps converge the illumination, whereas the objective lens magnifies the image to view for observation. Condenser lenses in optical microscopes comprise glass and are present sub-stage; they converge the light coming from the light source. At the same time, objective lenses magnify the observed image. In electron microscopes, condenser, and objective lenses are electromagnetic lenses that bring electrons to a thin beam to produce images.
What type of lens is a condenser?
Condensers are microscope optical devices that converge the illuminating light into a converged beam that illuminates the specimen. Optical microscopes have glass condenser lenses, while electron microscopes use electromagnetic lenses as condensers.
Is condenser lens concave or convex?
Condenser lenses play a significant role in converging the light rays to project them onto the sample; a convex lens provides the converging mechanism. Most condensers comprise two plano-convex lenses with the convex sides facing each other.
Is objective lens concave or convex?
While the focus of objective lenses is to magnify an object and not to converge the light from the illumination source, they are also convex lenses. Optical microscopes use objective lenses of short focal lengths to provide high power and magnification. The action of objective lenses increases the magnification of the sample and sends it to the eyepiece for observation.