Night Vision Blemishes and Black Spots: What Is Normal, What Is Damage, and When to Walk Away

The following is a guide to understanding what is normal, what is damage and when it is time to walk away when it comes to night vision blemishes and black spots.

Night vision blemishes are easy to spot and difficult to analyze, which causes nerves. A small black dot may be a normal cosmetic tube spot in a PVS-14. It can also be a sign that the seller is concealing a more serious problem, the optic is dirty, moisture is inside the device or the tube has been damaged by bright light.

Don’t panic, that’s the important thing. It is the inspection that is important.

Each night vision tube inspection is done in the same manner: clean the external optics, focus the tube properly, view a uniform low-light background, note the visibility and assess the blemish by size, location, how it moves, how much it costs and what is disclosed. A tube doesn’t have to look pristine for it to be useful. However, sellers must be truthful about what they are selling.

The following tips are related to analog image-intensified night vision, such as commonly used PVS-14 style monoculars and binocular systems. Diagnose the sensor, pixel, and display failure modes of digital night vision and thermal devices differently.

The Short Version

Small and stable night vision blemishes may be normal, if they are located near the outer edge of the image and were disclosed prior to purchase. Spots on the tubes, fixed-pattern texture and minor edge imperfections are not necessarily signs of failure.

Be cautious with:

• Large center-zone night vision black spots
• Signs of obvious burn or reticle shaped shadows
• Bright spot or emission point that remains constant during the night
• Extreme shading or moisture marks or abrupt changes in image.
• Blemishes that occurred post impact/recoil/water exposure/bright-light exposure.
• No clear photos of the tube and no Spec sheet (where one should exist) and no return option on a used device

When buying used night vision, make sure you see through-the-tube photos and/or video on a plain background, request the tube spec sheet if available, compare the image at various focus settings, and make sure you write down exactly what the seller says.

What Night Vision Blemishes Actually Are

Tube Blemishes vs Dirt on the Lens

However, not all dark spots are within the image intensifier tube. Marks that could be mistaken for tube defects can be caused by dust on the objective lens, lint near the eyepiece, fingerprint, dried water spots, dirty sacrificial windows, lens caps, and focus mistakes.

Check the external glass and accessories, don’t assume the problem is the tube. If possible, get rid of unneeded filters or sacrificial lenses, clean only in lens-safe ways and retest the image. If the spot moves, breaks up or can no longer be seen when refocusing or cleaning an external surface, it is probably not an internal blemish.

If the image is just soft, smeared or too hard to determine, go back to how to focus night vision before buying it!

Why Image Intensifier Tubes Are Not Perfect Screens

Analog night vision is not a telephone screen. An electro-optical tube that is used to amplify small quantities of light. In this process, the small manufacturing artifacts, tube spots, shading, fixed-pattern texture, and edge artifacts may be present even if the device is working correctly.

Not all defects are acceptable, however. It’s like you are looking at it as a field tool, not a phone screen. The acceptable standard is determined by the quality of the tubes, the grade of the tubes, manufacturer’s policy and vendor selection standards.

NV Guide USA has a good guide to how image intensifier tubes work, for more details on the underlying mechanisms. The practical question here is easier: Does the artifact impact use, price, warranty or trust?

Why Location Matters More Than Panic

Location is important as your eye makes use of the center of the image most. Small dark dot toward the outer edge could not show up in actual use. A similar location near the center of the image can be distracting while navigating, scanning, aiming passively via red dot, and reading terrain detail.

The specific wording of the warranties differ but the field logic is the same: center defects count more than edge defects.

Common Things Users See Through Night Vision

Small Black Spots

The most frequent problem is small night vision black spots. These can be referred to as PVS-14 black spots, PVS-14 blemishes, dark dots, or night vision tube spots.

Cosmetic spots are often those that are small, stable, disclosed, and at the periphery of the image. It’s more significant if the mark is big, new, in the center, in groups and/or does not match the seller’s pictures.

Larger Dark Patches or Shadows

There are various reasons for a larger night vision dark spot. This could be caused by debris, lens obstruction, moisture, tube shading, damage or a serious defect inside the tube.

Test patch on various backgrounds. Check focus/diopter again. Check for condensation, fogging, water seepage, or broken glass. If a dark area appears to be a sharp pattern from a reticle, light source or stationary bright object, then it is possible night vision tube damage and qualified support is required.

Bright Spots or Emission Points

A fixed night vision bright spot may be more alarming than a typical dark speck. A true night vision emission point is a bright point that can be seen in the tube image, for which no light source can be found in the scene. Some bright specks may be a transient reaction to light, reflections, or background, but a bright speck which persists over a long time at a fixed point is not good.

Avoid testing by shining bright lights at the device. Work in controlled, safe low-light conditions and refer to device manual. If the bright point remains in the same position, becomes larger, or flickers, or if it was not provided, consider it a support or warranty problem.

Honeycomb or Fixed-Pattern Texture

There is a slight fixed pattern or night vision honeycomb pattern, particularly when viewing a plain surface, and this is noted by some users. This may be due to the microchannel plate structure or night vision fixed pattern noise (FPN) appearing at a particular gain and light level.

But a slight texture doesn’t necessarily indicate an inferior tube. May be more apparent on a plain wall than out in the field. But heavy FPN noise can be distracting and should impact on price.

Edge Distortion, Shading, or Vignetting

Some night vision edge distortion or slight darkening (shading) may be less serious than a problem in the center image, but it is not unimportant, and may be noticed at night. Origin of edge issues may be from optics, tube characteristics, alignment, accessories, helmet position or user setup.

If the helmet needs to move around, the edges can become very distorted making it less comfortable. Visible edge issues remain and hinder consumer trust when selling.

Flicker, Flashing, or Sudden Image Changes

Not all picture changes are bad! The image may pulse or move due to auto-gating, ambient light changes, weak batteries, dirty contacts, loose battery caps or mount problems. Sudden new dark patches, intermittent failure or flashing that happens at steady state should be investigated.

Blemish Zones: Why Center Spots Matter More

Zone 1: The Center of the Image

The focus is in the center. Detail obscuration, passive aiming disruption or distraction while driving, or obscuration of small items is considered to have real field impact when a center-zone blemish interferes.

If it’s a large blemish in the center, the pricing should be reduced, it should be a factor in whether you return the item, and the spec sheet or warranty terms should be carefully read.

Outer Zones: Still Relevant, Usually Less Critical

Imperfections are more acceptable in the outer zone. The speck of dark near the edge may be barely noticeable when the scan is conducted normally. However, several big edge spots, too much shading, obvious distortion or a blemish that will distract you from using the device should be part of the negotiation.

Match Expectations to Tube Grade and Price

A top quality, hand selected white phosphor tube should not be treated like a "bargain used" with known blemishes. If there is a spec sheet for the tube, use that. It can’t necessarily answer all cosmetic questions but it can help you compare performance, grade and expectations. For a more comprehensive spec breakdown, visit NV Guide USA’s article on how to read night vision specs (the numbers that really matter).

How to Inspect a Night Vision Tube Before You Buy

Ask for Tube Photos Against a Uniform Background

For used night vision inspection, request clear thru-tube pictures/video of NV on a plain, evenly lit surface. Spots that are covered by grass, trees, brush and stars can be exposed by a uniform background.

Request the Spec Sheet When Available

Inquire about the spec sheet for the tube. Not all second hand devices will have one, but if the seller says they have a premium tube then the documentation is important. It may be useful to verify the type of tube, serial information, performance data and occasionally blemish information.

Check the Same Spot at Different Focus Settings

Focus changes shall be a part of a practical PVS-14 tube inspection. First adjust the diopter and then move the objective from close to distant. If the location on the screen changes significantly with focus, or that the location moves or disappears after cleaning an exterior surface, this is likely caused by dirt or optical debris. A blemish on the inside of the tube is typically permanent.

Compare Low-Light and Slightly Brighter Conditions

Some artefacts are more prominent under certain gain and light conditions. Very low light may highlight scintillation and noise while slightly higher safe conditions may help with spotting spots. Avoid use of analog night vision while looking into sun, headlights, weapon lights, visible lasers or strong IR sources.

Document What You See

When purchasing, hold on to those documents:

• Date and time of the inspection
• Lighting condition + background
• Gain setting (if applicable)
• Focus and diopter notes
• Check out the photos or video through the tube.
• Housing, objective, and eyepiece photos
• Seller’s description of blemishes, hours, damage and warranty
• Tube serial/spec sheet information (where available)

No big deal for an honest seller if he/she documents a costly product.

Normal Blemish or Real Damage?

Usually Normal or Cosmetic

Minor outer-zone blemishes, mild fixed-pattern texture and imperfection disclosed up front may be acceptable. If the price is fair, then a tube with a blemish can still be utilized.

Concerning

Be wary of large blemishes in the center-zone, bright spots after exposure to bright lights or impact, extreme night vision shading, bright points that don’t fade, moisture marks or unclear terms such as ‘normal for night vision’ without photos.

Deal Breakers for Most Buyers

If there are obvious reticle burns, large dark areas in the center of the device, or growing defects, intermittent tube failure, moisture inside the device, or the lack of basic documentation of a high dollar device or no-return sale with the seller refusing to send clear pictures, most buyers should walk away.

Used Night Vision Buying Checklist

Questions to Ask the Seller

Ask direct questions before payment:

1. What type/housing is it?
2. Does it have a spec sheet for a tube?
3. Are there any PVS-14 blemishes, tube spots, shades or bright points known?
4. Do the photos reflect current times and the exact device was used?
5. Has a bright light, lasers, water, heavy recoil, or impact been experienced?
6. Was it worn on the helmet or in the hand or attached to a weapon?
7. Do hours exist or is the time history not known?
8. Are warranties or vendor supports still available?
9. What are the return policies if the image is not the one specified in the listing?

Photos and Videos to Request

Ask for photos of the exterior housing, photos of the objective and eyepiece, through-the-tube photos with a plain background, a short video, if applicable, information on the gain behavior, and serial/spec details that the seller can share without problems. If you’re using binoculars, request each tube individually.

How to Judge Price Against Imperfections

Just because the tube is flawed doesn’t mean it’s a bad purchase. If the blemish is cosmetic and disclosed and priced for this, it might be the right tool. But there’s resale value, too: Even if you can deal with that spot, the next person may put a huge mark down on it.

When to Walk Away

When the seller avoids taking pictures with a uniform background, doesn’t provide basic information about the tube, tries to rush you to the decision, displays photographs from another tube, or considers all that you see as "normal" without any proof, walk away.

Troubleshooting Before You Blame the Tube

Clean the Lenses Safely

Lens-safe cleaning procedures should be used and do not use aggressive solvents, scraping or disassembly. Dirt from outside can look like dirt from inside! Once you’ve bought it, proper cap, case, battery, and storage habits are important and are covered in the guide on how to transport and store night vision gear.

Recheck Focus and Diopter

Poor focus may exacerbate the appearance of dust, grain, edge distortion and noise in low-light conditions. Now focus the objective for the distance of the object being viewed, after setting the diopter for the eye.

Change the Background

A uniform surface displays spots. They are concealed among a mess of a field scene. Use both: one to spot the blemishes the other to indicate if they impair use.

Check Battery and Contacts

Some image instability is due to power considerations and not to image intensifier tube blemishes. Use a known good battery, check the cap and contacts, and test handheld before mounting, external packs or cables are added.

How Blemishes Affect Real Field Use

Hunting and Scanning

The outer-zone spot is not significant for hunting and scanning purposes. Since a center defect can be right on top of the detail you are assessing, it is different.

Helmet-Mounted Movement

Comfort and clarity are key with helmet mounted night vision. Distracting center mark, excessive edge distortion, or extreme shading can cause eye strain and diminish confidence when walking. For those considering either mono or binocular, the NV Guide USA guide on PVS-14 vs dual-tube night vision can help inform that bigger purchase.

Buying for Resale Value

When the device is operational, visible blemishes have an impact on resale. Documentation, honest photographs and a clean inspection record preserves value.

Preventing New Damage After Purchase

Avoid Bright Stationary Lights

Bright-light exposure and burn is in addition to normal cosmetic blemish, and do not leave analog night vision pointed at bright stationary lights, lasers, headlights or the sun.

Use Caps, Store Correctly, and Remove Batteries

Keep dry, remove batteries and store them, and use caps and cases. When using night vision devices in rain or humidity, boats, or wet fields, know night vision waterproofing and the capabilities of your specific housing.

Do Not Mount Unrated Devices on Heavy-Recoil Rifles

Not all NVS are created equal, so don’t put all guns on all night vision devices. Recoil rating, mount compatibility, and manufacturer guidance are important.

Reinspect Periodically

Get baseline after-purchase through-the-tube photos. If a spot is discovered later, you’ll be able to tell if it’s a new spot or it was just noticed.

Final Verdict

Not everything that is a night vision blemish is tube failure and not everything that is a night vision black spot is a deal breaker. Real image-intensified devices may exhibit small, stable, disclosed outer-zone imperfections that are considered normal.

However, blemishes are never something that can be overlooked when it comes to a costly night vision purchase. Remove dirt from tube artifacts, make judgement about size & location, look for bright points & burn patterns, compare with documentation, and make decision based on clarity, disclosure, price, warranty & intended use. If the seller doesn’t show you the picture, if he/she is dodging your direct question, or if he/she wants top dollar for a questionable tube, skip it.