Focus

• One function of the coarse adjustment knob is to put an object under a microscope into focus. The adjustment knob moves the objective lens vertically to put a slide into focus. This will only give a rough estimate of the focus for the object; you must then use the fine adjustment knob to focus a clear image. You'll also use the coarse adjustment knob when changing objective lenses. The focus point of a new lens will be slightly different than the previous lens.
  
  

Finding Depth

• Some specimens have a lot of depth to them. Microscopes can help see elements of a specimen at different depths. For thick slides, you can use the coarse adjustment knob to scan through the depth of the slide to see the various parts. For thinner slides, you'll use the fine adjustment knob for this purpose.
  
  

When to Use

• A common concern for people new to using a microscope is when to use the coarse adjustment knob. Always use this knob when changing objective lenses. Sometimes, there will be a definite image with a smear of color that is out of focus. In this instance, use the coarse adjustment knob to find out what the unfocused element is. The coarse adjustment knob is used more with a dissecting microscope than with a compound light microscope.
  
  

Warnings

• All tools have a proper way to operate them to avoid breakage. The coarse adjustment knob physically moves the objective lenses up and down. If you push the objective lenses into a slide, you might break the slide. To avoid this result, only use the coarse adjustment knob when looking through the lower powered objectives. Use only the fine adjustment knob to focus a specimen when using an oil-immersion lens.