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Imaging/Focusing Microscope Objectives, Oil Immersion
100X Plan Achromat
100X Plan Fluorite
100X Plan Fluorite
Did You Know?
Multiple optical elements, including the microscope objective, tube lens, and eyepieces, together define the magnification of a system. See the Magnification & FOV tab to learn more.
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Example of an Oil Immersion Objective Design
(See Objective Tutorial Tab for More Information About Microscope Objective Types)
Thorlabs offers oil immersion objective designs from Olympus and Nikon. The majority of the objectives are plan fluorite objectives, while one (RMS100X-O) is a plan achromat design. For details about the differences between these types of objectives, please see the Objective Tutorial tab above.
These microscope objectives should be used in applications like traditional and multiphoton microscopy, confocal imaging, and optical tweezers, and are suitable for a variety of imaging modalities, including epi-illumination, oblique illumination, brightfield, and DIC applications. These infinity-corrected objectives have optical elements with an ultra-wide broadband AR coating, designed for use with either 180 mm or 200 mm focal length tube lenses.
The Olympus objectives on this page have RMS (0.800"-36) threading, and the Nikon objective has M25 x 0.75 threading. When choosing a microscope objective, it is important to keep in mind that objectives are often designed to integrate with a particular manufacturer's microscopes and are not necessarily interchangeable due to tube length differences and variations in thread pitch or diameter. Please note that the performance of each objective may vary from the engraved specifications when integrated with components and systems from different manufacturers. See the Magnification and FOV tab for more information.
Note: These microscope objectives serve only as examples. The format of the engraved specifications will vary between objectives and manufacturers.
Types of Objectives
Thorlabs offers several types of objectives from Nikon, Olympus, and Mitutoyo. This guide describes the features and benefits of each type of objective.
Dry or Oil-Immersion Objectives
Plan Achromat and Plan Apochromat Objectives
Plan Fluorite Objectives
Glossary of Terms
M = L / F .
The total magnification of the system is the magnification of the objective multiplied by the magnification of the eyepiece or camera tube. The specified magnification on the microscope objective housing is accurate as long as the objective is used with a compatible tube lens focal length.
Numerical Aperture (NA)
NA = ni × sinθa
where θa is the maximum 1/2 acceptance angle of the objective, and ni is the index of refraction of the immersion medium. This medium is typically air, but may also be water, oil, or other substances.
FN = Field of View Diameter × Magnification
Coverslip Correction and Correction Collar (Ring)
When viewing an image with a camera, the system magnification is the product of the objective and camera tube magnifications. When viewing an image with trinoculars, the system magnification is the product of the objective and eyepiece magnifications.
Magnification and Sample Area Calculations
The magnification of a system is the multiplicative product of the magnification of each optical element in the system. Optical elements that produce magnification include objectives, camera tubes, and trinocular eyepieces, as shown in the drawing to the right. It is important to note that the magnification quoted in these products' specifications is usually only valid when all optical elements are made by the same manufacturer. If this is not the case, then the magnification of the system can still be calculated, but an effective objective magnification should be calculated first, as described below.
To adapt the examples shown here to your own microscope, please use our Magnification and FOV Calculator, which is available for download by clicking on the red button above. Note the calculator is an Excel spreadsheet that uses macros. In order to use the calculator, macros must be enabled. To enable macros, click the "Enable Content" button in the yellow message bar upon opening the file.
Example 1: Camera Magnification
Example 2: Trinocular Magnification
Using an Objective with a Microscope from a Different Manufacturer
Magnification is not a fundamental value: it is a derived value, calculated by assuming a specific tube lens focal length. Each microscope manufacturer has adopted a different focal length for their tube lens, as shown by the table to the right. Hence, when combining optical elements from different manufacturers, it is necessary to calculate an effective magnification for the objective, which is then used to calculate the magnification of the system.
The effective magnification of an objective is given by Equation 1:
Here, the Design Magnification is the magnification printed on the objective, fTube Lens in Microscope is the focal length of the tube lens in the microscope you are using, and fDesign Tube Lens of Objective is the tube lens focal length that the objective manufacturer used to calculate the Design Magnification. These focal lengths are given by the table to the right.
Note that Leica, Mitutoyo, Nikon, and Thorlabs use the same tube lens focal length; if combining elements from any of these manufacturers, no conversion is needed. Once the effective objective magnification is calculated, the magnification of the system can be calculated as before.
Example 3: Trinocular Magnification (Different Manufacturers)
Following Equation 1 and the table to the right, we calculate the effective magnification of an Olympus objective in a Nikon microscope:
The effective magnification of the Olympus objective is 22.2X and the trinoculars have 10X eyepieces, so the image at the eyepieces has 22.2X × 10X = 222X magnification.
Sample Area When Imaged on a Camera
When imaging a sample with a camera, the dimensions of the sample area are determined by the dimensions of the camera sensor and the system magnification, as shown by Equation 2.
The camera sensor dimensions can be obtained from the manufacturer, while the system magnification is the multiplicative product of the objective magnification and the camera tube magnification (see Example 1). If needed, the objective magnification can be adjusted as shown in Example 3.
As the magnification increases, the resolution improves, but the field of view also decreases. The dependence of the field of view on magnification is shown in the schematic to the right.
Example 4: Sample Area
Sample Area Examples
The images of a mouse kidney below were all acquired using the same objective and the same camera. However, the camera tubes used were different. Read from left to right, they demonstrate that decreasing the camera tube magnification enlarges the field of view at the expense of the size of the details in the image.
These objectives provide 40X, 60X, or 100X magnification, flat images across the entire visible spectrum, high numerical aperture values, and excellent resolution. The RMS40X-PFO, RMS50X-PFOD, RMS100X-PFO, and RMS100X-POFD are plan fluorite designs, while the RMS100X-O is a plan achromat design. The differences between these designs can be found in the Objective Tutorial tab.
All of these objectives are suitable for brightfield microscopy, and all but the RMS100X-O are suitable for DIC microscopy. Additionally, the RMS60X-PFOD and RMS100X-PFOD objectives feature a built-in iris diaphragm, which is designed to be partially closed during darkfield microscopy in order to preserve the darkness of the background. This is absolutely necessary for high numerical aperture (above NA = 1.2) oil immersion objectives when using an oil immersion darkfield condenser. For ordinary brightfield observations, the iris diaphragm should be left fully open. The iris diaphragm adjustment is pictured above and to the right.
These objectives use standard RMS threading. To use these objectives with a different thread standard, please see our RMS Thread Adapters.
Objective manufacturers recommend using immersion oils from the same manufacturer for best performance; Thorlabs offers a variety of immersion oils below. A protective cap is also available for these objectives; see below for details.
This objective provides 100X magnification, features high transmission, particularly at UV wavelengths, and produces flat images across the field of view, making this objective well suited for use in laser scanning microscopy. It is designed for DIC microscopy, but can also be utilized for brightfield microscopy, fluorescence, and polarized light microscopy. The high NA of this objective also makes it suitable for Optical Tweezer applications. These objectives use M25 x 0.75 threading, which can be converted to other thread standards using Thorlabs' selection of M25 x 0.75 adapters.
This objective is designed for use from -18 °C to 60 °C (0 °F to 140 °F) and is not recommended for use at extreme temperatures. Objective manufacturers recommend using immersion oils from the same manufacturer for best performance; Thorlabs offers a variety of immersion oils below.
These Microscope Immersion Oils are designed for use with Oil Immersion Microscope Objectives. Placing an oil medium between the front surface of the objective and the cover glass allows the objective to achieve a high numerical aperture, maximizing light collection by the objective. To minimize refraction of light from the sample, the refractive indices of immersion oils are very close to those of cover glass.
Immersion oils are available with low or very low autofluorescence. Autofluorescence is the natural fluorescence emission of the oil when exposed to light. Each immersion oil has a different level of background emission, which either increases or decreases the contrast of the image; oils with very low autofluorescence are optimized for use in sensitive or UV fluorescence microscopy applications.
To clean immersion objectives after use with immersion oils, use a soft optical cleaning tissue such as our MC-5 premium lens tissues.