If you’ve heard your lab instructor or teacher referring to the “coarse adjustment knobs” or to the “fine adjustment knobs”, you may be wondering ‘what is a coarse adjustment and fine adjustment and what’s the difference?’
Coarse adjustment, using the coarse adjustment knobs, raises and lowers the stage more rapidly. Fine adjustment knobs are smaller knobs and are also used to raise and lower the stage but more slowly and in a more controlled manner under higher magnifications.
In this article, we will discuss when it is appropriate to use each, and where they are located on the microscope.
What Is a Fine Adjustment Knob?
The fine adjustment knob is a part of the microscope that is used for focusing the finer details of a specimen being viewed. Objectives like low power and high power objectives are used with a fine Adjustment knob for a clearer image in higher resolution.
What Is a Coarse Adjustment Knob?
The coarse adjustment knob is a part of the microscope used when focusing specimens. This knob is generally used when viewing specimens with scanner objective (4X).
Other objectives like low power and high power objectives are used with a fine Adjustment knob for a clearer image in higher resolution.
Where Are The Coarse Adjustment And Fine Adjustment Knobs Located?
The coarse adjustment knob on most microscopes is along the lower middle part of the arm of the microscope.
The coarse adjustment knob is the bigger of the two knobs and is located closest to the arm of the microscope. The fine adjustment knob is the smaller of the two knobs and is located further away from the arm of the microscope.
Most coarse and fine adjustment knobs are built with coaxial control in line with one another so you can easily switch from using the coarse focus adjustment knob to using the fine focus adjustment knob.
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Some microscopes will still have two distinct knobs with the smaller being the fine adjustment knob and the larger, being the coarse adjustment knob.
The coaxial knob allows the user to change between the knobs by feeling instead of having to pull away from the eyepiece to look for the desired knob.
You will notice that when you turn the knob it moves the stage (or the body tube depending on the type of microscope you have) much faster than the fine focus knob (the smaller one).
The fine adjustment knob will be the smaller of the two knobs and when you turn the knob you will notice that the movement is much slower and more controlled.
With some fine adjustment knobs, you will hear a slight clicking noise. This is an auditory indicator to give the microscope observer an auditory indicator relative to the act of turning the knob.
Some coarse and fine adjustment knobs will come with a numeric dial that helps the user with precise adjustment settings. These are typically only on more advanced compound microscopes.
How To Use Coarse Adjustment And Fine Adjustment Knobs?
If the eyepiece on your microscope is built facing away from the arm of the microscope then turning the knob away from you will raise the stage and turning the knob towards you will lower the stage.
If you are looking at it from the side turning the knob clockwise will raise the stage and turning the microscope counterclockwise will lower the stage.
The basics of using a microscope tell us that we should start with the lowest power objective first and with the stage at its lowest position.
So if you have just loaded a new specimen and slide you need to make sure you have the lowest power objective engaged and the stage at its lowest position and use the coarse adjustment knob first to quickly get the specimen in focus.
Once you get the specimen in focus you can make positional adjustments to the slide using the mechanical stage X – Y translational knobs or position the slide manually using your fingers.
After you have the slide positioned and centered on your area of study or inquiry you need to engage the next higher-power objective lens.
This time you will use the fine adjustment knob slowly to focus your image under the higher power objective. Once you find focus the process repeats with the fine focus adjustment knob on the next higher power objectives.
How To Troubleshooting Microscope Focusing & Gears Tension
If microscope focusing gears or tension on these focusing devices is too tight or too loose the microscope stage can drift or cause problems getting a microscope image into focus.
This microscope stage drift is typically caused by a loose focus mechanism. On a compound microscope, the tension adjustment is usually on the inside of the coarse focus next to the body of the microscope.
Turning this tension adjustment clockwise will tighten the tension (required if the stage is drifting). Turning the tension adjustment counter-clockwise will loosen the tension (required if it is hard to move the focus mechanism).
Occasionally if the microscope does not have a tension adjustment next to the body, the microscope focusing adjustment is performed by holding the left side of the focus mechanism stationary while slowly turning the opposite side of the microscope focusing mechanism.
Consult your microscope owner’s manual for the correct format to use when adjusting the focusing tension on your compound microscope.
Difference Between Coarse and Fine Adjustment
Just about any device can be adjusted to suit the preference of the user. In most devices, there is only one adjustment knob for each controllable element. But in certain cases, there are two adjustment knobs; labeled as coarse and fine adjustments.
The main difference between the two is in how large the increment is in each step. With a coarse adjustment knob, a small movement results in a large jump, while the opposite is true with a fine adjustment knob.
Another difference between coarse and fine adjustment is the range that they have.
The coarse adjustment covers the entire range from minimum to maximum. In contrast, the fine adjustment only covers a fraction of the entire range.
The bare minimum range for the fine adjustment is the discrete step increment of the coarse adjustment, in order to cover the entire range. It can also be larger, depending on the designer of the device.
To clearly illustrate how coarse and fine adjustments work together, picture an adjustment that has a range of 0 to 100. For coarse, each step increments by 10, and 1 for fine.
If you only have a coarse adjustment, it will be quick and easy to go from minimum to maximum but you cannot achieve an exact value like 15 and you have to settle for either 10 or 20.
If you only have a fine, you can select any value but you have a lot of steps to take in order to go from minimum to maximum. If you have both coarse and fine adjustments, you get the pros of both.
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