The following two methods are typical for deepening the depth of field.

(1) Increase the depth of field distance.

(2) Narrow down the optical path *For information on aperture, please refer to “What is depth of focus/depth of field?”

 

This time I will explain (1).

 

 

■ Relationship between depth of field and working distance

Below is a spec table for lenses of the same manufacturer, same series, and same magnification (X4).
The longer the W.D., the deeper the depth of field.

 

 

 

 

■Actual measurement of depth of field due to differences in working distance

 

Comparative imaging using lenses from the same manufacturer and series but with differing working distances, observing a glass scale with a 0.2mm pitch tilted at a 45-degree angle and viewed from directly above.

 

 

 

 

(1) Observation using a lens with an optical magnification of 6x and a working distance of 40mm.

 

 

If you determine that the focus is aligned with one increment (0.2mm), then the depth of field can be calculated as 0.2mm x (1/√2) = 0.14mm.

 

 

(2) Verification using a lens with an optical magnification of 6x and a working distance of 110mm.

 

 

If you determine that the focus is aligned with two increments (0.4mm), then the depth of field can be calculated as 0.4mm x (1/√2) = 0.28mm.