Having just written my first post for the Microscope Challenge, it is not easy comparing microscopes to know what you want. Below I am going to outline how to know microscope magnification, and what different levels of magnification can get you. I am not an expert on microscopes, just someone who spent the last 3 hours trying to understand what people are most likely to see at each level of magnification when it comes to microbes. I will make edits to this post as people correct me.
Magnification
This one took me some time, but shout out to HighschoolScience101 Youtube channel for simplifying this.
On a microscope there is the eyepiece lens and the objective lens which give you the total magnification.
This is a Brockscope (not sponsored) these are very popular with Nature centers because they do not require electricity to work and make good field microscopes.
The top of the brass pipe is where the eye piece is, on a Brockscope, that is 5x. The bottom of the brass pipe is where the objective lens is which here is 10x. That means this microscope has a magnification of 50x.
On compound microscopes such as this one, you have 3 objective lenses that you can switch between. If the lenses are 4x, 10x, and 20x, with an eyepiece of 10x, the microscope has a magnification of 40x, 100x, and 200x.
What can you see with different magnifications?
This took lots and lots of research, and it's still fuzzy. The best answer I could get related to the Field of View. The diameter of the field of view is how large in millimeters or micrometers the microscope is looking at. Based on that number, I looked up the size of several common micro-items to get an idea of what field of view would be necessary to see them.
According to one website I was reading, it is common for the field of view at the eyepiece to be 20, by dividing 20 by the magnification of just the objective lens, you get the diameter for the field of view.
See Table below.
Objective lens | Field of view in millimeters | Field of view in microns |
4x | 5mm | 5000 microns |
10x | 2mm | 2000 microns |
20x | 1mm | 1000 microns |
40x | 0.5mm | 500 microns |
100x | 0.2mm | 200 microns |
What does this all mean? Using an objective lens of 4x, you are looking at a space 5mm wide, but when you switch to a 20x, the space you are viewing is 1mm wide.
Let's put this into context. Using the compound lens example from before, our eye lens is 10x, and the objective lens can be 4x, 10x, or 20x. That means this microscope can see at 40x, 100x, or 200x. This Image from microbehunter.com shows how a Varroa mite looks different at different magnifications. To help give context to the image below, a varroa mite lives on a bee and is about 1.1 mm long and 1.7 mm wide.
Seeing 1.5mm object magnified at these levels, let's take into consideration the size of other common things you might want to see under the microscope.
Example | Size in millimeters | Size in microns |
Fingerprint | 10 | 10,000 |
Frog Eggs | 1.6 - 3.5 | 1600 - 3500 |
Varroa Mite | 1.5 | 1500 |
Beach Sand | 0.1 - 20 | 100 - 2000 |
Human Hair | 0.1 | 100 |
Table Salt | 0.12 | 120 |
Pollen | 0.015 - .2 | 15 - 200 |
Plant Cell | .01 - .1 | 10 - 100 |
Animal Cell | 0.01 - 0.03 | 10 - 30 |
Bacteria | 0.0001 - 0.01 | 0.1 - 10 |
Size does not correspond to magnification directly
An Objective lens at 40x would give you a field of view of 500 microns across, with an eyepiece of 10x, that would be 200x magnification. 200x magnification is a lot, but many beginner microscopes will barely reach that. I was worried 500 microns would be too big of a scale to see a small 100-micron object, but from what I have learned, the diameter across the microscope does not mean the limit to how small you can see. In fact several articles said you can see human hair at 100x just fine. All this to say, use the numbers above to compare object to object based on the mite image. But to help you further, check out this website on microscopes and the images below also helped me understand different sizes and what a microscope is capable of seeing. I hope this helps!
Sources that helped me understand Microscopes and the relative size of objects:
How much magnification do I need?. Microbehunter Microscopy. (n.d.). https://www.microbehunter.com/how-much-magnification-do-i-need/
Libretexts. (2021, March 19). 1.1: Introduction. Biology LibreTexts. https://bio.libretexts.org/Learning_Objects/Laboratory_Experiments/Microbiology_Labs/Laboratory_Exercises_in_Microbiology_%28McLaughlin_and_Petersen%29/01%3A_Introduction_to_Microscopy_and_Diversity_of_Cell_Types/1.01%3A_Introduction
Measuring the size of specimens viewed with a microscope and adding scale bars to photomicrographs. Motic Microscopes. (2024, October 8). https://moticmicroscopes.com/blogs/articles/measuring-the-size-of-specimens-viewed-with-a-microscope-and-adding-scale-bars-to-photomicrographs
Microscope images at different magnifications. Microscope Images at Various Magnifications | Microscope World Resources. (n.d.). https://www.microscopeworld.com/t-microscope_images.aspx
Microscopic Measurement. Essentialpathology.info. (n.d.). http://www.essentialpathology.info/gradingschema/index.html?HelpfulMethods
Rachael. (2022, May 23). What is a microscope?. Microscopy4kids. https://microscopy4kids.org/microscope/
Understanding the difference between magnification and resolution in scanning electron microscopy. Nanoscience Instruments. (2024, March 28). https://www.nanoscience.com/blogs/understanding-the-difference-between-magnification-and-resolution-in-scanning-electron-microscopy/
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