The electromagnetic spectrum is composed of a range of different wavelengths or “colors” of light energy. A spectral remote sensing instrument collects light energy within specific regions of the electromagnetic spectrum. Each region in the spectrum is referred to as a band.

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Low powerobjective microscopefunction

The most important parameter of a microscope objective is the numerical aperture (NA). NA measures the microscope objective’s ability to gather light and determines the resolution of a microscopy system.

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What are the objective lenses on a microscopeclass

If high resolution data shows you more about what is happening on the Earth’s surface why wouldn’t you always just collect high resolution data (smaller pixels)?

Compared to NAIP, Landsat data are collected using an instrument mounted on a satellite which orbits the globe, continuously collecting images. The Landsat instrument collects data at 30 meter spatial resolution but also has 11 bands distributed across the electromagnetic spectrum compared to the 3 or 4 that NAIP imagery has. Landsat also has one panchromatic band that collects information across the visible portion of the spectrum at 15 m spatial resolution.

The Moderate Resolution Imaging Spectrometer (MODIS) instrument is another satellite based instrument that continuously collects data over the Earth’s surface. MODIS collects spectral information at several spatial resolutions including 250m, 500m and 1000m. You will be working with the 500 m spatial resolution MODIS data in this class. MODIS has 36 bands however in class you will learn about only the first 7 bands.

The optical aberration corrections determine the optical performance of an objective lens. According to the degrees of the aberration corrections, objective lenses are typically classified into five basic types: Achromat, Plan Achromat, Plan Fluorite (Plan Semi-Apochromat), Plan Apochromat, and Super Apochromat. Choosing an objective with a proper aberration correction level will help you build a microscopy system at a reasonable cost.

What are the objective lenses on a microscopeanswer

The most common immersion media are air, water, oil, and silicone. Choosing the appropriate objective designed for your immersion medium will result in higher resolution images.

What are the objective lenses on a microscopegive

To better understand multispectral remote sensing, you need to know some basic principles of the electromagnetic spectrum.

Types ofobjective lenses

If you recall, you learned about raster spatial resolution when you worked with lidar elevation data in previous lessons. The same resolution concepts apply to multispectral data.

Many objective lenses are corrected for infinite conjugate distance, while others are designed for finite conjugate distance applications. Compared to infinite conjugate objectives which need a secondary lens (also called tube lens), a finite conjugate objective can generate an image of a specimen by itself. A finite conjugate objective, as shown in Figure 1, is a good, economical choice for a simple microscopy system.

The spectral resolution of a dataset that has more than one band, refers to the spectral width of each band in the dataset. In the image above, a band was defined as spanning 800-810 nm. The spectral width or spectral resolution of the band is thus 10 nm. To see an example of this, check out the band widths for the Landsat sensors.

Objectivelens magnification

Often when you work with a multispectral dataset, the band information is reported as the center wavelength value. This value represents the center point value of the wavelengths represented in that band. Thus in a band spanning 800-850 nm, the center would be 825 nm.

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While a general spectral resolution of the sensor is often provided, not all sensors collect information within bands of uniform widths.

NA is commonly expressed as NA = n × sinθa where θa is the maximum 1/2 acceptance angle of the objective, and n is the index of refraction of the immersion medium. The limit of resolution of a microscope objective refers to its ability to distinguish two closely spaced Airy disks. Resolution (r) = λ/(2NA) Where r is resolution (the smallest resolvable distance between two objects), and λ is the imaging wavelength. The higher the NA, the better the objective resolution.

Objective lenses are used in microscopy systems for a range of scientific research, industrial, and general lab applications. A microscope objective is typically composed of multiple lens elements and located closest to the object. There are so many types of microscope objectives available, choosing the right objective can help you produce good quality images at a reasonable cost. When choosing a microscope objective, we will need to consider a number of factors including conjugate distance, numerical aperture (NA), magnification, working distance, immersion medium, cover glass thickness, and optical aberration corrections. In this article, we will discuss how to choose the right microscope objective.

High powerobjective microscopefunction

When talking about spectral data, you need to understand both the electromagnetic spectrum and image bands. Spectral remote sensing data are collected by powerful camera-like instruments known as imaging spectrometers. Imaging spectrometers collect reflected light energy in “bands.”

A dry objective is designed to work with the air medium between the specimen and the objective lens, while an immersion objective requires a liquid medium to occupy the space between the object and the front element of the objective for enabling a high NA and high resolution. Figure 4 shows the oil immersion objective, which can collect more light (i.e., have a higher NA) compared to a dry objective.

Usually the working distance (WD) refers the distance from the front lens element of the objective to the observed object when the object is in sharp focus. Objective lenses with long working distance are needed for many scientific research applications such as atom trapping and analyzing fluid samples that require putting an object in a chamber. The resolution of a microscopy system can be significantly affected if the observed object is not placed on the designed object plane, especially for an objective with high NA.

Objective lenses are used to magnify an image. In addition to numerical aperture, magnification is also an important parameter. The objective magnification typically ranges from 4X to 100X. As the image sensor size or eye observed area is fixed, the field of view of a microscopy system changes with the magnification of the objective lens. Typically a lower magnification objective lens will have a larger field of view and lower resolution, and a higher magnification objective lens will have a smaller field of view and higher resolution. The diameter of the FOV can be calculated by using the following formula: FOV= FN/Mag The field number (FN) in microscopy is defined as the diameter of the area in the image plane that can be observed through the eyepiece or image sensor.

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In the previous weeks of this course, you learned about lidar remote sensing. If you recall, a lidar instrument is an active remote sensing instrument. This means that the instrument emits energy actively rather than collecting information about light energy from another source (the sun). This week you will work with multispectral imagery or multispectral remote sensing data. Multispectral remote sensing is a passive remote sensing type. This means that the sensor is measuring light energy from an existing source - in this case the sun.

SO offers a wide range of objective designs, which provide various degrees of optical aberration corrections for supporting different needs, such as achromatic objectives (the cheaper objectives) for laboratory microscope applications and long working distance apochromats (expensive objectives) for biological and scientific research applications. We can help you choose or design a properly corrected objective lens for meeting your application requirements.

Objective lenses microscopefunction

Remote sensing data can be collected from the ground, the air (using airplanes or helicopters) or from space. You can imagine that data that are collected from space are often of a lower spatial resolution than data collected from an airplane. The tradeoff however is that data collected from a satellite often offers better (up to global) coverage.

The spatial resolution of a raster represents the area on the ground that each pixel covers. If you have smaller pixels in a raster the data will appear more “detailed.” If you have large pixels in a raster, the data will appear more coarse or “fuzzy.”

Infinity-corrected objectives are ideal for research-grade biomedical industrial applications especially when additional components (such as filters, dichroic mirrors, polarizers) are needed in the microscopy system. Adding optical plate components in the infinity space (shown in the Fig.2 labelled as “Parallel Optical Path) between the infinity-corrected objective and tube lens will not introduce spherical aberration, or change the objective’s working distance.

A band represents a segment of the electromagnetic spectrum. You can think of it as a bin of one “type” of light. For example, the wavelength values between 800 nanometers (nm) and 850 nm might be one band captured by an imaging spectrometer. The imaging spectrometer collects reflected light energy within a pixel area on the ground. Since an imaging spectrometer collects many different types of light - for each pixel the amount of light energy for each type of light or band will be recorded. So, for example, a camera records the amount of red, green and blue light for each pixel.

For example the Landsat 8 satellite has a 16 day repeat cycle for the entire globe. This means that you can find a new image for an area, every 16 days. It takes a lot of time and financial resources to collect airborne data. Thus data are often only available for smaller geographic areas. Also, you may not find that the data are available for the time periods that you need. For example, in the case of NAIP, you may only have a new dataset every 2-4 years.

NAIP imagery is available in the United States and typically has three bands - red, green and blue. However, sometimes, there is a 4th near-infrared band available. NAIP imagery typically is 1m spatial resolution, meaning that each pixel represents 1 meter on the Earth’s surface. NAIP data is often collected using a camera mounted on an airplane and is collected for a given geographic area every few years.