Night Vision Lens Guide

Keep in mind, these are simplified definitions meant to give a more practical understanding—rather than strict optical engineering terms—to help you choose a lens from an operational perspective.

Objective Lens:  The front lens of your night vision device. Focus for the device is adjusted here.

Ocular Lens or Eyepiece Lens: The rear lens of your night vision device. This sits inside the diopter housing.

Diopter Housing: This is the part of the lens you twist on the rear to adjust the magnification of the projected image to your eye. In layman's terms, this is how you get the NOD to be adjusted for your eye prescription.

Limiting Resolution: When talking about resolution for lenses and NODs, we are not talking about resolution in the same sense as what we’re used to, which is display resolution. Display resolution counts pixels on a screen (2160p or 4k, 1080p or HD, as an example), limiting resolution is how well an optical system can resolve detail or separation in a subject. 

For the most part NV, this is tested with a variant of a 1951 USAF resolution test chart inside the Hoffman 126A. As the pairs get smaller, the lenses are limited in what they can resolve, the better the lens, the more apparent the differences are.

The Hoffman 126A Digital Test Rig we use to test every NOD we build will have a built-in resolution chart. In this example, OE (Optronics Engineering) Lenses are used on the left while a Noctis lens is used on the right. Already apparent is the greater rendition of details in the Noctis lens set. 


The image above shows the real-life differences between an OE lens (lower limiting resolution). and a Noctis (formerly Carson) US-Milspec lens with a much higher resolution. The Noctis image is far clearer even though the intensifiers used in this test are the same.

Light Transmission: For night vision, light transmission refers to how much light enters the lens for the intensifier to work with. All lenses, by nature of light passing through a medium, will impact light transmission. Lenses with higher transmission may appear to have a brighter image with more detail in darker areas due to the lenses allowing in more light for the intensifier to work with. Generally, lenses with higher light transmission will squeeze more performance out of a tube and will allow the tube to have less scintillation (noise) and more detail in ultra-low-light environments.

Quality night vision lenses must find a careful balance of allowing in the most light while reducing the amount of unwanted flares and blooming, managed by careful use of optical design and coatings.

Contrast: Contrast is the difference in luminance that makes objects stand out from one another. If you ever see an image, be it on night vision or a phone screen, that’s washed out, that's a lack of contrast.

Lenses with a better rendition of contrast have a starker difference between the lightest and darkest areas for better ID of subjects.

While the clarity of the images is somewhat comparable, the main difference will be the contrast. Notice how the Noctis image has much darker shadows and more defined highlights. 

Distortion: Distortion deals with how “flat” the image is rendered. There are various different kinds of optical distortion, fisheye or barrel distortion actually is more common with wide FOV lenses in cameras, and causes the image to bow outwards. Pincushion distortion is more common in zoom lenses and causes the image to bow outwards. Moustache or wavy distortion is a combo of the two and usually is the least desirable.

All NV optics in our experience will have a bit of pincushion (not fisheye!) distortion because they will all be magnifying lenses, the rear lens actually seeks to correct the curvature of the output screen on your image intensifier while zooming into the image for you to see. 

Quality NV lenses will seek to minimize this distortion as much as possible to give users the most natural looking image.

 This image shows the distortion characteristics of each lens (OE vs Noctis). The distortion pattern actually follows a pincushion pattern in all NVG lenses due to the nature of them being zoom lenses. In this case, the Noctis lens produces a far "flatter" image.

Flare Resistance or Flare Suppression: This aspect dictates how well a lens controls bright light sources, lenses with good flare suppression are less prone to washout (veiling glare), lens flares, and other undesirable artifacts caused by using night vision in mixed lighting environments or force on force situations.

Flare suppression characteristics are determined by many factors including the optical stack, anti-reflection coatings, and the glass quality. 


Off axis flaring as seen in the above image is the "washout" effect often seen in mixed lighting environments. Lenses that have better flare control (Noctis in this example) will render the image much clearer than lenses with poor flare control. 

Eyebox, Exit Pupil, and Eye Relief: Often used interchangeably but have different definitions. The exit pupil is the width of a cone of light available at an eye relief. The eye relief is the distance last from the surface of the optic which the user can see at the full viewing angle.

Eyebox is a more generalized word for the effects of the two above terms and is a way of saying how well the optic can render an image to our eyes when moved away from its ideal position.