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CAN RESOLUTION BE DESCRIBED IN TEXT?
Probably not but here goes -
Resolution and detection tend to go hand in hand and can at times be difficult to separate.
Simplistically, resolution with Image Intensifying night vision is governed by the number of lines per millimetre, while in Thermal Imaging it is pixel size and number, FPA size. From there it gets a bit more complicated. We also need to be aware of DRI in regard to thermal.
Detection, Recognition and Identification apply specifically to thermal. This is explained in "Facts about Thermal Imaging".
The comparisons below are somewhat vague as it is hard to compare all specifications of Thermal equipment at the same time.
The thermal referred to below is a commercial grade monocular, 17 micron, 384 X 288 FPA with a 50 MM focal length lens, producing a nominal 4 X optical magnification compared with a 4 X magnification image intensifying unit.
Keep in mind that most of what is to follow is also contained in other pages.
With all the types of Night Vision equipment available these days, not in respect to makers but purely generations, you need to know and understand what people are trying to tell you.
Unfortunately a lot of the advice and view points you get do not give the full picture, or make a proper comparison, some being comments made by users without having access to ALL types of systems to make a proper comparison.
For example, image intensifying NV is regarded as having superior resolution compared to thermal.
Yes and no, it is true to some extent, but you need to be aware that commonly quoted statements are made without distances or conditions being taken into account or how you should actually make a comparison.
It becomes more difficult to provide a simple statement when you introduce the variations of generations of image intensifying gear, magnification and the amount of ambient light or external Infrared sources etc.
With this sort of equipment the low generations (Gen 1) have only low resolution and low light gain but, comes with a low price.
This is where resolution and detection becomes confusing. You need to be able to detect / see the target before you can talk about the resolution (how sharp the image appears).
If you have trouble seeing the target because it is too dark, then you can never really say how sharp it is. So you need to have a lot of illumination or a higher Generation unit to be able to see it well first. This then introduces a higher resolution tube, e.g. having more lines per mm.
So can we really try to interpret resolution????
Using the above basic optical magnification of 4X and no external Infrared source with image intensifying equipment, and a kangaroo (3/4 grown), a standard Australian object -
Gen 1, with 35 - 45 line pairs per millimetre and light gain of between 900 and 1000 times, with a full moon you should see the kangaroo at a hundred meters, at about 50 metres you will see it is a kangaroo and a reasonable image.
With starlight only you will barely, if at all, see the animal at 100 m.
Using the specified thermal (4.1 X optical) and no light at all, no moon and even with heavy cloud cover, you will see a very good image at 100 m as well as seeing it quite well at 2 - 300 meters.
OK, we have a slight problem here, the thermal will cost many times that of any Gen 1.
Gen 2+, with 45 - 64 line pairs and 22,000 to 25,000 times light gain, same conditions, you might see a workable image at a couple of hundred meters in full moon, (see "Important note" below) and possibly detect it to maybe 200 m and maybe, only just detect it at about 150 m or there about in starlight only. Even with the better resolution and light gain, a kangaroo will be rather hard to actually pick out from the inherent shade and shadows in the overall field of view.
Thermal, the same as above.
Thermal still about twice the price of commercial grade image intensifying NV or about the same as professional grade NV. (Some commercial grade NV Gen 2+ can have as little as only 45 lp / mm!)
Gen 3, "starting" level, minimum of 60 line pairs per mm and a light gain of between 50,000 to 70,000 times. Full moon, 250 m, with a fair image, again, depending on how well it will stand out in the surroundings. No moon, again, maybe 200 meters, and average image, if you can actually pick the animal from the background..
Thermal performance, same as above.
Commercial thermal cost is now similar.
Now jump straight to the top end of Gen 3.
Gen 3, line pairs 68 to 72, and a light gain within the same range.
Resolution will be improved but detection distance will be much the same as the light gain is still within the given range of 50,000 to 70,000 times, there are other factors as well that will also give added improvement besides just lp/mm.
Thermal, again still the same as above, but commercial grade is now cheaper by comparison.
It now probably time to consider a professional grade of thermal, but the comparison price will jump to about double that of the tubed unit.
Price comparisons will vary considerably as the exchange rate on the $Au changes.
IMPORTANT NOTE. As mentioned above, seeing "the kangaroo" with ANY Image Intensifying (NV) depends HUGELY on the background as a kangaroo tends to blend into the shading of even a grassy pasture. Technically it will be well visible, but no quite so in practical terms!
High contrast animals (large black pig) will fair a bit better with regard to standing out against the background.
The above distances are only approximate and will vary considerably under varying conditions!
Additional factors also apply, such as suitable optical magnification for the distances mentioned combined with the associated lens speed.
The standard "line pairs / millimetre" (lp / mm) test chart ( USAF 1951 ) is subject to the operators interpretation of the lines resolved. Even so it is a good indication of the units ability to resolve the stated line pairs and resolution.
So now you are be fully aware (?) that resolution is difficult to describe at differing distances and differing conditions with different grades of NV and also Thermal.
In all grades of NV, "noise" will become a factor with low light levels, (but not so with thermal) which in turn degrades the image to varying degrees, obviously the higher light gain the lower the light level can go before this becomes a problem.
While we are on the subject of Line Pairs, these are not a fixed manufactured thing.
All they refer to is the ability to differentiate between the standard patterns on the test sheet.
A different situation, even a high end Gen 3, even with Autogating and a high spec of say, 72 lp / mm will drop to a very low lp / mm of around 20 - 30 when subjected to a bright light, such as vehicle headlights appearing into view, not an overall scene brightness, the ability to see "high" definition will drop until the bright light has been removed.
“Auto Gating”, is a system that turns the sensor on and off rapidly is designed to minimize the problem of shut down and also prevent tube damage.
Site updated, SEPTEMBER 22, 2021.