What is depth of focus or focus tolerance?

The depth of focus refers to the distance along an optical axis required by a laser beam to double its focus area - starting from the focus in the focal plane. The depth of focus and its basic physical makeup are important in laser technology, as they are used to determine the right lens for the respective application.

Terminology: Depth of focus

The depth of focus depicts the range in the space of an image in which an object is adequately sharp and in focus. This is why the “depth of focus” is also called the depth of sharpness. This means that an imaging system (in our case, the laser beam) can be adjusted in the range of image depth without blurring the result.

Effects of focus tolerance on the laser beam

Focus and focus tolerance can be directly compared if you want to cut or engrave with a laser. Choosing the right lens for your application is equally as important as optimizing the focus.
In order to achieve a fine and highly detailed laser engraving, you will need a lens with a smaller focal length. However, if you are cutting thicker material, a lens with a large focal length is ideal. In our focusing example, we use the 1.5-inch lens for a CO2 laser. This low focal length lens provides finer detailed engravings of the graphic due to a resolution of more than 500 dpi.

The downside you face with decreasing the focus diameter is that the depth of focus also decreases, i.e. it needs to be focused more precisely.
Contrary to the 7.5-inch lens, the larger the focal length, the higher laser power allowed. For example, cutting acrylic sheets up to 1 inch thick.

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