Analog night-vision devices (NVDs) have a naturally limited depth of field. Once the focus point is set, only a certain distance range remains sharp, while objects closer or farther become blurred. This is not a flaw — it is an inherent property of the optical system.

1. Why depth of field is limited

An analog NVD focuses in a single plane. If the user focuses on a distant target, near objects appear blurry, and vice versa — exactly like the human eye.

2. How reduced-aperture devices work

An aperture reducer limits the amount of light reaching the lens, which leads to:

  • Increased depth of field — more objects at different distances stay acceptably sharp;

  • Decreased image brightness — less light results in a darker, noisier image.

3. When an aperture is genuinely useful

Aperture devices are valuable when:

  • there is ambient illumination (urban conditions, starlight, moonlight);

  • the user must see near and far objects simultaneously (driving, patrol work);

  • performing administrative or search tasks.

In total darkness they are less effective due to light loss.

4. Practical ways to increase depth of field

  • standard day caps with small holes;

  • MATBOCK Tarsier Eclipse — fully adjustable aperture with sacrificial window;

  • Phokus Hoplite — fixed-aperture flip cover;

  • improvised scope caps with drilled openings (cheap but imprecise).

5. How to decide whether you need an aperture

Ask yourself:

  • Do you often need both near and far objects to be in focus?

  • Will you operate in environments with enough light?

  • Do you need additional lens protection?

  • Do you want smooth, adjustable aperture control?

6. A simple pre-purchase test

Use an inexpensive scope cap with a small hole.
If the improvement suits your needs — invest in a proper dedicated device.