Learning Optics with Austin: Lesson 18 – Microscope Objectives

Microscope objective lenses are a classic example of optics in our lives. The function of the microscope is to enlarge objects our eyes cannot see. Unlike telescopes which enlarge far away objects, the sample observed by the microscope is close to the lens. Microscopes also correct aberration, which otherwise would lead to blurry images. Achromatic (doublet) lenses only correct for aberration of two wavelengths of light whereas apochromatic (triplet) lenses correct for 3 or more wavelengths.

One of the factors that go into designing an objective lens is the magnification. The colored bands on the outside of the microscope indicate the magnification of the lens. The standard magnification bands are as follows: red band = 5x, yellow = 10x, green = 20x, blue = 40-60x, white = 100x. Thus, if a lens has a green and yellow band, the magnification would be 30x.

Another factor to consider in designing an objective lens is the working distance (WD). This is defined to be the distance from the front of the objective to the sample when in sharp focus. Working distance is related to the numerical aperture (NA) which is calculated by the formula NA = n * sin(θa), where n is the index of refraction. When in air, n = 1. To obtain a greater refractive index and increase the numerical aperture, sometimes the objective is immersed in a liquid such as oil or water. While aberration, magnification, working distance, and numerical aperture are not the only variables to consider when designing a microscope, they are key characteristics that one should look for.

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About the Author

Austin from Shanghai Optics Inc

Hello! My name is Austin and I am the host for this blog. I graduated from Rutgers in May 2021 with a Bachelor’s degree in Statistics-Mathematics and History. I interned during the summer of 2021 at Shanghai Optics working on data cleaning and analysis. I was later offered to work full-time starting in September. While my initial role was in data analytics, I realized that my knowledge of the company’s products was quite shallow as a key skill for any well-trained data analyst is to know your data. That’s how I got started on my journey in learning about optics.

I found physics interesting but challenging in high school. I did not particularly enjoy classical physics and a seminar in quantum mechanics flew over my head in college. As I see first-hand how our optics works in different applications, I’m quickly beginning to realize that Photonics has the potential to shape the present and the future.  Because of my newfound enthusiasm, management took notice and I am fortunate enough to begin a Physics/Photonics class sponsored by Shanghai Optics in the fall of 2021. This blog is part of my experience in taking the class and sharing with you all the wealth of knowledge I’m acquiring!

Aside from optics, some of my personal interests include studying history and going on hikes. Both activities are great opportunities to talk with other people so feel free to ask me any questions on my personal interests or the materials I post!

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