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OK, so how much can you see?
This page, to a large extent is the same as the previous page on Resolution.
IT SHOULD BE NOTED HERE that with all the developments in software / firmware, in thermal imaging, there has been some significant changes in performance regarding image quality / resolution. Therefore some of the details below while not incorrect, can now be bettered by the newer devices from reputable manufacturers.
When time permits this page will be fully updated, but in the meantime what is indicated below is still generally applicable.
Image intensifying has not moved forward in real performance, and the current devices are about as far as can be achieved.
When it comes to performance there is much talk in some circles about there being no benefit going past Gen 2+, because "Gen 3 will not provide much improvement over 2+".
YES there IS benefit, while some Gen 2+ tubes may indeed have the same number of lp / mm, they still have only 22,000 - 25,000 X light gain, whereas Gen 3 will have 50,000 - 70,000 X light gain! The resolution may theoretically be the same, but due to the lower gain you will not see anywhere near the same distance under comparable light conditions. (You will not have any of the other "improvements" that comes with the Generation rise either).
You cannot compare Gen 2+ (or any other type of NV) using additional light, with Gen 3, unless you also provide the same amount of additional light for the Gen 3 !
I have and use both Gen 2+ HPT and Gen 3 from the same manufacturer, both with 61 lp / mm, but the Gen 2+ HPT will NOT detect / see anything like the same distance, due to the lower light gain. ( identical optical magnification! )
I suspect that this argument is probably promoted by people who either do not understand there is more than just line pairs per mm in the specifications, have never actually compared both, or, maybe they do know, but can only supply Gen 2+, and are unable to supply Gen 3 items. So therefore will not acknowledge Gen 3 superiority (??)
The one high specification Gen 2 + are the, Photonis XR 5 tubes. Although these are only Gen 2 +, their manufacturing processes will match Gen 3 tubes for resolution and signal / noise ratio, but they do not have the same light magnification ability, it is still down at Gen 2 level. Only the resolution, lp / mm, and signal to noise is higher than Gen 2 +.
It is common practice to state only the lp / mm figures in most advertising, but you need to explore all the figures yourself. Not hard to find, shown above anyway.
It is normal to have a range of lp / mm and light gain within each generation, both are due to normal manufacturing variations.
Manufacturers with a good reputation will supply a detailed specification sheet with each Gen 2+ and Gen 3 tube supplied.
Now it is time to think about what you will actually see, if and when you do "detect" our kangaroo. It will not matter with any type of NV when the range has extended out to even half the maximum detection distance, if the kangaroo is stationary and bent over feeding! It will just be a "lump" but thermal will tell you there is a "hot spot" and therefore it is not a bush, stump or whatever. OK once it stands up or moves things get a little easier.
So resolution or not, thermal, even commercial grade will tell you more than image intensifying, especially at extended distances, the kangaroo we have been talking about will be seen as a hot spot at 600 - 700 m whereas even Gen 3 image intensifying you would be lucky to even notice it regardless of that "better" resolution it is deemed to have.
Don't confuse detection with recognition or resolution!
As I have shown previously on other pages, cattle on clear pasture are identifiable at about 800 m with commercial grade thermal at 4.1 X. Sure they are bigger than "our" kangaroo, but with Gen 3, @ 6 X optical, 68 lp / mm, an FOM of 1938, a light gain of 52,000, with starlight only, the same cattle are barely detectable as indistinct shadows, NOT identifiable as anything.
Anything said here should not to be taken that image intensifying products of any Generation are not going to be of use, they are (Except Gen 1), you just need to understand them, and that is no different for thermal imaging.
As a note, thermal will see into shadows / between bushes, whereas image intensifying will not, even when using extra IR, due to the IR glare off the "face" of the surrounding objects, negating any anticipated "benefit", just as a spotlight will do.
I have mentioned before, I personally use thermal, in both commercial and professional grade as well as professional Image Intensifying. (And have used digital as well, which I have not included in this discussion). Digital has much the same characteristics of detection etc as most image intensifying NV, being somewhere between Generation 1 and Generation 2 equipment (at this time of writing) although it is always improving.
Therefore I believe I can make a qualified judgement as to which is more effective.
You need to be cautious about the use of extra IR with Gen 3 gear, not that it will hurt it too much, but it tends glare off the foreground if it is too bright will not help at longer distances at all, unless it has a very narrow beam that will highlight a small area only .
Optical magnification helps with thermal over digital magnification (zoom), and you need to be remember that the "f" the lower the number the better, preferably f1:0 if it is possible or even practical. Anything over f1.4 for thermal will start to be detrimental.
Basically, the greater the available light input (sensitivity) for all image intensifying regardless of the number of line pairs per mm, the better the image and detection distance as this will reduce the "noise" on the image you get with low light.
A problem with obtaining more optical magnification is the focal length increases and at the same time the f number also increases. To overcome this, the lens diameter must increase. The "f" number is calculated by dividing the focal length by the lens diameter. Or if you have the f number you want to obtain, divide the focal length by the f number and see how big the lens diameter will need to be. For example, a 6 X optical magnification scope with a focal length of 165 mm and a lens diameter of 97 mm, gives us an f 1.7 lens. As you can see by this, the lens diameter becomes very large if you want a "fast" lens and high magnification.
Should you say OK, I want an f 1.0 lens on that 6 X scope, the lens would need to be 165 mm in diameter!
There are some NV scopes, mainly digital, these days at 10 X, to keep the lens size under control the f number suffers. When this occurs the magnification might just be what you want but the light "input" is reduced, so you will not get the overall benefit you were hoping for.
Loosely speaking when you are comparing thermal NV images, using a 640 x 480 FPA, 17 microns, a 50 mm focal length lens for example, will provide a nominal 2 X optical magnification and 3 X optical for a 75 mm lens.
Things can be modified by selecting an FPA size of 384 x 288, again 17 microns, providing greater magnification, 3 X for 50 mm focal length and 4,5 X for the 75 mm lens, at the same time not losing resolution with the smaller FPA, other than a small amount of the image "quality" as it is interpolated to the OLED screen for viewing, e.g. you may not have quite as nice an image, although you may not see a huge loss and gained a bigger target image.
You do have a narrower field of view though, which in my opinion (from a users perspective) is of little consequence, and be more than compensated for by the extra optical magnification(??)
The matter of resolution between the two FPA sizes can be hard to visualize in text, but you will have exactly the same number of pixels in the "wanted target" with both FPA sizes when using the same pixel size!!
Having said all that, the best option performance wise, it is better to stay with the 640 x 480 FPA and go to the longer focal length lens, staying at the same optical magnification, better image and have the benefit of a better image when using the next "zoom" feature, (if you can justify the extra expense).
There are no free lunches, including with night vision equipment.
While you are researching night vision, a piece of advice. Be wary of the "rave reviews" given on forums and magazine advertising etc for low specification items, especially those relating to Gen 1, as they are generally written by first time purchasers who have never previously used night vision and are therefore stunned by what they can see for the first time.
For instance I recently saw a review on a 4X Gen 1 scope, the reviewer gave it 5 stars, as he could ID a coyote at 75 yards with full moon ?? With full moon you don't even need NV at that distance.
Gen 1 has a place (?) for limited observation but it will never provide satisfactory results for a serious user without massive amounts of additional IR light or large amounts of moonlight. Even with low resolution thermal will get an indication that something is "there" but not much else, especially with the slow lenses normally associated with low resolution units.
These ramblings here are intended to outline the main points to look at when investigating the resolution / detection ability of a night vision product, there are other factors that are important in the overall outcome as well. Things like E.B.I, (Equivalent Background Illumination), Radiant Sensitivity, Photocathode Sensitivity, Signal to Noise etc. All these factors have an effect, and they follow the trend of improving as the Generations and "grades" within Generations rise, even though the line pairs and light magnifications will vary within each specified generation.
While having nothing at all to do with resolution, thermal will allow a quick "scan" of the surrounding countryside, both close and far as you will see "hot spots" quickly without needing to actually look for a target. This is primarily because you are seeing a heat source, critical focusing for distance is not required, just focus for a general mid distance. You really only need to focus on a target for identification purposes, if required, once it has been detected. Image intensifying equipment will show up possible targets reasonably when you are working in clear field or paddock and only where there is a lot of contrast to allow an object to really stand out.
When considering "how much will you see" it is vitally important to be aware that manufactures ALWAYS select a unit that is at the highest end of tolerances, and ONLY film in ideal conditions ( Low humidity, best contrasting scene, very close target etc ) that way producing the best image possible. YOU will not always have all that working for you in your "corner".
The following sample images are random ones collected from time to time an are NOT carefully selected for "viewing"
Again, please note these images are greatly enlarged for viewing and therefore are of much lower resolution that that seen directly with the unit used to produce them.
Site updated, SEPTEMBER 22, 2021.