Parfocal means what?

Parfocal means what?

• A. You must refocus significantly when switching objectives
• B. You can switch from one objective to another and re-focus very little
• C. It refers to the parabolic shape of lenses
• D. It defines the focusing mechanism for condenser

Answer: (B)

Parfocal means you can switch from one objective to another and re-focus very little. In a light microscope, objectives have different focal lengths, so the plane of focus shifts when you change magnification. When the objectives are parfocal, the image stays near sharp focus after changing objectives, so you typically only need a small adjustment with the fine focus knob. This saves time and keeps the specimen roughly in the same position on the stage. The other statements describe things that aren’t parfocal: needing substantial refocusing, or referencing the parabolic shape of lenses, or tying the term to the condenser—these aren’t what parfocal means.

Parfocal means you can switch from one objective to another and re-focus very little. In a light microscope, objectives have different focal lengths, so the plane of focus shifts when you change magnification. When the objectives are parfocal, the image stays near sharp focus after changing objectives, so you typically only need a small adjustment with the fine focus knob. This saves time and keeps the specimen roughly in the same position on the stage. The other statements describe things that aren’t parfocal: needing substantial refocusing, or referencing the parabolic shape of lenses, or tying the term to the condenser—these aren’t what parfocal means.