In an attempt to demystify thermal imaging and night vision systems in practical terms, it is hoped these notes might go some way in helping to overcome those "dark" secrets and misinformation that continues to surround them.
The following pages are long, and may be considered boring to a casual reader, but might possibly contain some specific information that could be of interest to a serious reader.
YOU HAVE BEEN WARNED !
The following sections discuss
Thermal Imaging or Image Intensifying -
Facts about thermal -
Using night vision -
Considerations for a night vision scope -
What you will see -
Sample images -
Image below, courtesy "Guns America"
Before we start, I believe it is important for the reader to be well aware that there is a "LOT of EXPERT" information provided on forums and industry web sites, regarding "seeing and detection distances etc." with night vision and thermal imaging.
A number of the claims and advice provided, can only be described as figments of wild imagination probably brought about by the use of "funny weed" and are simply not achievable.
There are at times the reverse, where it is said that it is all useless and no help in identifying a target reliably. You just need to understand what the benefits and limitations are.
One Australian business, claiming to be a major supplier of thermal equipment, the owner / technical adviser does not even know or understand which way IR frequencies vary with respect to temperature increases.
Don't be fooled by some well known brands, they are not necessarily all high specification items as they would like you believe.
Advertising is an art form.
Hopefully after going down these pages it will all become a little better understood.
First of all we need to understand that "Night Vision" was intended to enable us to see in the dark, not to be a long range observation device as are telescopes, binoculars etc.
Certainly as the technology advances we are able to see greater distances than in the past, and we are able benefit from it all.
OK, now let us look at what various types of night vision will give us.
Thermal imaging detects the "heat" in all objects, living or not, you need no light at all.
Image intensifying requires light, IR and or visible, that is "multiplied" by the tube fitted in the device.
With thermal, obviously the greater the temperature difference, the greater one object will stand out from other surrounding objects.
For example, on a hot day in the "field", a small animal will not be easy to see against the surrounding hot ground, rocks etc. whereas at night in the same location it will stand out clearly.
But let’s think about that for a moment, why would you need thermal or any other night vision system in the daylight anyway?
A "live target" among rocks etc. that is a similar size to the rocks, that are still hot from the days sun, can be a little hard to distinguish until the rocks have cooled somewhat, therefore providing a greater temperature difference between them and the target. Naturally enough a moving target will be obvious. (Rocks do not normally move ! ....Hopefully)
Something that should be pointed out here regarding thermal, is that "detection" distances quoted by various manufacturers should be viewed cautiously, as they are calculated distances and NOT actual distances. Therefore some may be considered to be a little "generous" where one make of a particular specification will promote one distance while another with exactly the same specification, different one, as the user has no way of actually confirming the figures.
So in real terms one stating say, 1600 m will be no different in performance to another indicating 1800 m.
System sensitivity is of more concern, and yes, this should probably be included the "Facts about Thermal" page.
Other forms of night vision, ie. image intensifying, require some LIGHT, whether it is the ambient light generated by stars, moon or an external infrared light source, and they amplify whatever light is available.
Although the night is never TOTALLY dark, it will require no less than Gen 3, and at the same time will need at least, starlight available to produce a workable image, or an external IR light source, which in turn can create a problem with nocturnal animals (see below).
Digital however, only detects what the ambient or external light / IR intense enough to produce an image. This is limited by the sensitivity of the sensor fitted and does not "magnify" any available light.
Digital equipment should really be viewed as a consumer product at this time, due to its inherent requirement of very high levels of Infrared light to provide any worthwhile detection range at night. Therefore can hardly be considered real "night vision" regardless of what resolution quality it may or may not have.
I don't see why you would purchase a "night vision" product and then be required to provide illumination of some kind to make it work???
Remember, the actual IR light can be seen by nocturnal animals as well as the visible red light generated by the illuminator that is very visible and a high power illuminator will show an intense red light which can be seen extremely well from the "targets" direction.
"Covert" IR is less noticeable when viewed directly at the source but the IR light produced can still be seen by nocturnal animals.
This applies to any "NV" system requiring additional IR !
The general consensus is that Image Intensifying units will provide more detail or definition of the "target" when compared with most thermal imaging, this is an interpretation view point only, but regardless, you will still NOT see a "desired target" in dark shadows, whereas thermal will make these stand out and be seen without question. (See the above image)
For example, a high end Gen 3 unit can provide an exceptional image in the right conditions, but you will still need a high contrast "target" to stand out from the background and surrounding objects.
The higher specification models of thermal imaging can now provide the user with outstanding detail giving the best of both worlds.
There are units combining thermal and image intensifying NV, but unfortunately they are usually out of reach of the general "public", as are some of the new High Spec thermal only products.
Do not expect to get the same performance from a $300 NV item that you will get from one costing $30,000!
This in no way implies that ONLY professional grade equipment should be considered.
Commercial products are always a proposition in most situations, but $300 will not buy anything but toys.
Whatever produces the desired results and is within a budget is obviously the choice to make.
If you intend to make observations, for example, from inside a motor vehicle or inside a building, thermal imaging will not "see" through glass windows, while image intensifying can be used but with a reduction in performance.
When making a choice of a system type to use, remember that any type of night vision that requires some degree of light (image intensifying and digital), will have difficulty when trying to observe something or someone when they are partially covered or concealed behind bushes, trees, in shadows etc.
Thermal will "see" any part of the target that is not completely covered, even in total darkness.
The use of infrared illumination will only provide limited benefit when used in attempting to light up between the bushes. All that will be seen is the IR glare reflected of the face of the bush, just as that observed when using a spotlight in the same situation.
Having said that, a "hot" target completely covered by an object which prevents any heat being radiated, will not be seen with thermal imaging either.
Various "generations" of image intensifying night vision exist, these nominally start at Gen1, there is mention of Gen 0 at times, and go up to Gen 3, plus various "improvements" after that. Generation 4 * (see below) is also referred to at times but it is not an official classification.
The Generations relate to changes in design and their performance in low light conditions, and at the same time image quality improves accordingly.
The greater number of line pairs per mm (lp / mm) the better the image resolution produced but will not substantially increase the detection distance, unless you have increased light magnification as well.
There are other improvements as generations go up, such as signal to noise ratio which is an important part of seeing an object clearly, especially in adverse conditions.
Prices naturally increase relative to their performance. It is important to be aware of just what the differences actually are. Unfortunately it is difficult to explain all this in text. It is always beneficial to discuss this in detail with us prior to making a decision what may be applicable for the job at hand.
One difference between types of night vision systems that may influence selection for a shooter, is that with the use of IR illumination with image intensifying units, "eye shine" can be detected. Thermal imaging will not produce this effect, as no illumination is required, therefore there is nothing to be reflected back to the shooter.
A situation to consider, for instance, even a medium sized animal in a “clear” paddock with average pasture, at 100 – 200 +M, thermal imaging will clearly indicate a “target” is there, even partially obscured by grass or shadows, you may not see enough of it to properly identify what it is, but you will know it is there.
Changing from thermal for spotting to an image intensifying NV scope to shoot, a common suggestion, even with Gen 3, the "target" will tend to blend into the shadows and shapes in the grass and can be difficult to even see, (unless it is a high contrast target), even though it is widely accepted that this type of equipment will (supposedly) provide better definition of the target than thermal.
A classic example of how thermal will show up a target that may otherwise be missed with a quick scan of the surroundings can be seen in the image above. Just imagine how difficult it would be if the man was even just into the edge of the trees. Ref. Image Courtesy "GUNS AMERICA"
* Photonis have now released a "4G" tube (not "Gen 4") which has some modified specifications over their XR5 tubes. Basically the XR5 has better signal to noise ratio and an improvement to average lp / mm over "normal" Gen 2. There is also slight improvement to the EBI. Unfortunately the light amplification is still low (Gen 2 level). The 4G has the ability to use a longer wave IR. In my opinion it will not provide any real benefit to most users for the extra money required.