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View Full Version : Comparing models of NV- how to read and understand spot spec charts



Lowdown3
08-15-2020, 07:38 PM
New to night vision purchasing?

In this first one we will discuss blemishes and spot spec charts so you can understand how to interpret these and their importance.


Q: "Night vision is all the same right? A PVS14 is a PVS14 right?"

A: Big negative. All PVS14s are NOT the same. Just because it's called a PVS14 doesn't mean it's built to mil spec or even contains a tube worthy of being called a PVS14.



Q: "Why is the tube important, it's just one part right?"

A. The tube is the very heart of the unit and can be upwards of 90% of the cost of the unit. All night vision tubes come out differently when manufactured and are "graded" based on how well they perform (specifications) and how many flaws in the tube (blemishes) that exact tube has.

Blemishes are black spots in the tube which are a flaw in the manufacturing process. While all NV tubes have some sort of small blemish, they may be so small you cannot see them with the naked eye. They are graded based on SIZE of blemish and the LOCATION of the blemish. This is where you will see a "spot spec" guide that may look like this-

Zone 1- 0
Zone 2- 2
Zone 3- 2

What does that mean? The "zones" are locations within the tube. Zone 1 is the center and it is very important to have a clean Zone 1. If you envision large circles within the "circle" of the tube then Zone 2 is the next outer band from Zone 1, roughly a 1/3 of the way out from Zone 1. Finally Zone 3 is the far outside band- for example if you were looking at a round CLOCK, zone 3 would be where the numbers are located on the clock.

Blemishes (blems) are also further categorized by Size .003 to .006 are tiny and the smallest blemishes that can be measured. Often times your eyes cannot even make out these tiny blemishes. Many people argue that this size should be considered "pepper speck" and not even a blemish.

It's also important to remember that blemishes are inherent in all night vision tubes, they just may be so small you cannot see them with the naked eye. So a true "blem free" tube isn't out there. When you see someone say they have a "blem free" tube what they really mean is that it lacks any large blemishes.

Finally, a blemish is not a sign that your tube has failed or your tube is "bad." They are simply flaws in the manufacturing process. Just like there is no perfect diamond (ask your wife), there is no "perfect" Night Vision tube. This is the major point to remember as new purchasers expect perfection that doesn't really exist with analog technology.

Q: "So what should I look for in a spot spec chart when buying a unit?"

A: You should seek a grade of tube that is as CLEAN AS POSSIBLE. Definitely one that shows a clean Zone 1 Outside of Zone 1 you want as little as possible -and as small as possible-blemishes in the outer zones. Even if it's a "great deal" most people shy away from units advertising blemishes in Zone 1. Some of the worst deals out there right now show spot spec charts with blemishes in Zone 1 and LARGE blemishes in all the other zones-