The Importance of Depth of Field (Parfocal)

The Importance of Depth of Field

How much of your surgical view is in focus? And why is this important to you?

Depth of Field
                              Depth of Field

Because the less time you have to re-focus means faster surgery and less stress to you caused by muscle and eye fatigue 

Depth of Field (DOF) is The amount of your surgical view that is in focus 

Here is what you can do to maximize your Depth of Field and reduce constant focusing:

1. Initial focus should be done at the highest magnification 

2. This is called “Parfocality*” and this diagram shows how it works:

Diagram Explanation: if you focus on object #1 at low magnification (2x) your object will out of focus at 12x high magnification. If you start at high magnification and focus on object #2, you will be in focus throughout the range of magnification (#3).


The other action you can initiate is to reduce the amount of light into the microscope through aperture (iris) adjustment. Reducing the illumination can enhance the DOF.  To do this, most microscopes have auto iris and some have an additional manual iris.

Remember, Depth of field decreases with increasing magnification and aperture (iris) adjustment

Haag-Streit Surgical Microscopes have the best depth of focus allowing more anatomy in focus. For product information, please click on these links:

Spine Surgery
ENT Surgery
Ophthalmic Surgery

Chuck Luley

*Parfocal microscope objectives stay in focus when magnification is changed; i.e., if the microscope is switched from a higher power objective (e.g., 40×) to a lower power objective (e.g., 10×), the object stays in focus. Ideally, most bright-field microscopes are parfocal.