The parfocal distance, also known as the parfocalizing distance, is the vertical distance from the nosepiece mounting surface to the focused specimen. For most modern microscopes, this standard distance is 45 millimeters.
Why is a standard distance important?
A uniform parfocal distance allows objectives to be changed with minimal refocusing. This means you can use a series of objectives and quickly achieve focus with each one, even though they may differ in length.
Parfocal and parcentric
- Parfocal: objectives remain nearly in focus when switching magnifications
- Parcentric: the specimen remains centered in the field of view when changing objectives
Advantages
- Faster workflow when changing magnifications
- Consistent specimen positioning
- Greater efficiency in observation and documentation