OK, THERMAL

STARLIGHT ? ?    

NO.   Thermal does NOT require starlight, or any other kind of light to operate to it's full potential.

First of all, let's clear this up. Thermal devices are IR devices, regardless of what so many self proclaimed experts claim. 

They detect ONLY INFRARED, i.e. "HEAT". Heat IS INFRARED!!

Thermal devices detect IR in the far IR wave lengths, and NOTHING but INFRARED. For other than gasses, 8000 - 14000 nanometres.

Many wrongly refer to "image intensifying" devices, commonly referred to as "Night Vision", as IR, because they can "see" some IR wave lengths (Near IR). 

They need light of some type, visible light (Although low level) and yes, they can use the shorter wave lengths, (the higher IR frequencies closer to visible light and out to about 950 Nano meters) of reflected IR. 

We will only refer to un-cooled items here, as they are the types you will be using, as against those cryogenically cooled devices only used in fixed or semi fixed military situations. (With the appropriate price tag)

Unfortunately the specifications used in advertising for Thermal Imaging can be very misleading.  

Importantly, you need to understand what the "quoted" magnification actually means as this can appear very impressive.

For example, 3 - 24 X means 3 X optical magnification only. 

All the other figures are digital (Zoom) magnification, and they DO NOT / WILL NOT produce the same degree of clarity as optical magnification. 

Usually only the first step, at times the second step of digital zoom, with a current high spec device is of real benefit in most situations.

Be aware that digital magnification will magnify the atmospheric "interference" as well.

More on magnification later.

                                                     DRI

 DRI  (DETECTION, RECOGNITION, IDENTIFICATION) are commonly quoted figures derived by using the "Johnson Criteria" and indicate a range of distances that are based on two probabilities, of, 50% and 90% of accomplishing those tasks. 

THESE FIGURES WILL VARY CONSIDERABLY with differing atmospheric conditions etc. and therefore must NEVER be considered as absolute.

The Johnson Criteria is purely THEORETICAL, a CALCULATION ONLY, and has VERY LITTLE bearing on real life situations.

The figures quoted by GSCI are the average distance between the 50% and 90% distances referred to above. 

A major feature in promoting a product is to state the "DETECTION" distance. 

Detection means just that, detection, a few pixels and NOTHING else. 

The normal standard is to "detect" a man sized target (1.7 m x 0.5 m) or a NATO target, (2.3 m x 2.3 m) at a specified distance. 

Example, a MAN sized target @ 3330 m, NATO target @ 4500 m.  

All you will be seeing is a few pixels of a "hot" spot, you will NOT be seeing it as a "man", or whatever. 

From there you have "RECOGNITION", the distance, where you can recognize that it is a man / person (or whatever) but NOT who it is.

Then, comes "IDENTIFICATION", again the distance, which is often not provided, being considerably less than recognition. Identification is regarded as only identifying that a human "target" is a "good guy" or a "bad guy", again, NOT who it is.

Experience using thermal imaging will extend your own "Recognition" and "Identification" distances once you have become accustomed to how a person / animal moves, and reacts, combined with what you might expect to see in your area of operation.

When you investigate the D.R.I. figures for the different models with the same pixel size, and the same focal length and lens speed, you will find the D.R.I. figures are identical. 

There is no loss of DRI between the 640 X 480 and 384 X 288 FPA sizes.

A casual look at these figures, it may seem to suggest the 640 X  480 FPA will contain more pixels in the "wanted target" image than the 384 X 288 FPA, but this is not so.

The specific "wanted target" within that image, at the same distance with the same lens and either size FPA, that "wanted target" will contain no more or no less pixels than the other, regardless of what you might think.

When comparing figures provided by various manufacturers quoting the "same" specification products, most state an average figure between the 50% and 90% probability distances, while other manufacturers, generally those of a more specialist nature may give a more conservative figure.

This does NOT indicate a lower specification item, but a more realistic expectation of detection distances achievable under average conditions. 

Some manufacturers seem to stretch distances somewhat for advertising purposes.

Smaller "targets" will obviously need to be closer for all the above categories.

Remember these figures are calculations ONLY.

Another important piece of information is the operating or refresh rate, 

e.g.  7, 9, 30, 50 Hz and so on. 

What this means to the user is how smooth and realistic a moving image appears. 

Anything below 25 Hz (Standard video camera frame rate) produces a lagging image on a moving target, especially a fast moving one. Most available devices will now be 50 Hz. 

At first thought it would be fair to say that a "new picture", @ say, 9 times a second, an available rate for some imported products, would or should be fine. 

Sorry, no it is not, OK maybe for casual observations but not much more.

Probably not many 9 Hz devices are still available these days, but be aware.

The next thing to consider is the detector pitch and FPA (Focal Plane Array) size, in the past, thermal devices were commonly 25 microns with an FPA with 384 X 288 pixels. These days 17 um is the general "standard" pitch with 12 um becoming more common.  

When considering the difference in the quoted specification of the both FPA sizes you will find a noticeable variation in the quoted magnification between the two versions. 

For example, if you compare both, using a 50 mm focal length lens, an FPA with 640 X 480 pixels and a pitch of 17 microns you will have 2 X optical, where one of 384 X 288, also 17 microns, you will now have 3 X optical. You have approximately 50% higher optical magnification with the smaller FPA. 

This is because the larger FPA provides a wider field of view at any specified distance, which in turn produces a wider overall image compared with the "wanted target". (Difficult to explain in text).

By using the smaller FPA you are effectively producing a 1.5 X "zoom" from what you would have from the otherwise equivalent 640 X 480 unit.   This applies to all devices regardless of the lens length.   

The smaller FPA will exhibit some slight "degradation" of image quality due to the greater "expansion" of the image onto the viewing AMOLED screen, (just as it does when "zooming"). 

The higher magnification of the "target" may offset any degradation (??).

Now, if we refer to an FPA using 12 microns, these are smaller overall, even with the same number of pixels, they will have the same effect. 

All of these, if the pixels numbers are similar, they will give you an optical magnification approximately the same as one with 17 microns at one focal length higher. 

For example a 50 mm focal length lens with 640 X 512 / 12 micron pixels produces about 2.8 X optical.

To retain 3 X magnification with 17 microns, you need to go to a 75 mm focal length lens.

The common belief here is the smaller pixels will give a better image due to their smaller size.

This sounds like a great advance, BUT the 12 micron image, even with similar pixel numbers, when interpolated onto the AMOLED produces an image quality approximately identical to a 17 micron one due to the "stretching" of the image because the FPA is physically smaller.

Things are always improving, now a 12 micron FPA with the brands we supply, with their inbuilt image management does provide great value as the image "quality" is equivalent to the 17 micron models, but with the advantage of a 1.4 x higher magnification with a given focal length lens, and therefore a cheaper scope.

To achieve "better" image you need to go to a 12 micron sensor with the same overall physical size of the equivalent 17 micron sensor. This will provide what you hope to gain, but it will NOT provide any extra magnification. It will provide you with a very high price tag though (If you can actually find a device).

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  NOW LETS LOOK CAREFULLY AT MAGNIFICATION FOR A MOMENT.

It is in my opinion, based on years of using thermal devices, that the best all round general purpose magnification is 3 X obtained with todays specification products.

Although a new 12 micron sensor may be worth considering with it's inherent "extra" magnification. See below.

Why, you ask. OK firstly we will look at 17 micron units, and always combined with a 640 X 480 FPA. This will produce 3 X using a 75 mm focal length lens, a practical physical size. It will also give the user a large enough image to work with in virtually all situations.

A common request is for more magnification. 

Great, but you will need to step up to a 100 mm focal length lens, which is longer and at the same time, a bigger diameter to retain your overall sensitivity. 

Providing you a 33 % magnification gain, which may sound good, but in practical terms is it worth the extra size ?? 

A large somewhat cumbersome device in most situations.

Now if we were to go to 12 micron sensors and 640 X 512 pixels and still use a 75 mm focal length lens, you will now have approximately 4.25 X. 

Great, more magnification, AND you keep the physical size of the lens and therefore the overall scope size under control and still retain the same overall image quality.

Digital "zoom" still applies in all situations in all devices.

Regarding sensitivity figures often quoted, they are in most instances complete garbage. This is a complex situation and not well understood. (See below) 

Sensitivity and the lens. The "f" number (Speed of the lens not the focal length) of the lens governs the amount of thermal energy entering the unit just as it does with light in a camera.  

Consider heat (IR) and light as being the same, as they are the same, other than their wave length / frequency. 

System  sensitivity (Overall sensitivity) is determined by multiplying the FPA sensitivity in milliKelvins by the the lens "f" number squared. 

For example, a unit with an FPA sensitivity of 50 mK using an f 1.0 lens will have an system sensitivity of 50 mK. e.g. 50 x 1.0 x 1.0 = 50, whereas an f 1.3 lens would be 50 x 1.3 x 1.3 = 84 mK. 

If you jump to say, an f 1.5 lens you will now have a system sensitivity of 112 mK. This shows the decrease in the system or overall sensitivity with the "slower" lenses.

Don't be too alarmed about the overall system sensitivity, (within reason). 

While it may be reduced by the use of "slower" lenses, the only feature that is affected is the ability to see extremely small differences in temperature, e.g. the shading or slight temperature variations over an animals body.

All you will encounter is only a few 1/1000 thousandths of one degree difference ! 

A far more important factor in overall image quality, (image detail) is governed by the built in firmware / software in the device.

With professional grade thermal devices that may have an overall SYSTEM SENSITIVITY of around say, 85 mK will actually produce better, sharper, clearer and more detailed images than a device that has a supposedly superior sensitivity!

Don't confuse FPA sensitivity quoted, with system sensitivity.

There is NO USER that will actually SEE this difference in sensitivity.

On some forums there is almost hysteria when it comes to the FPA sensitivity !! 

Regardless, with all thermal devices there will be some "visible" losses at lower temperature things, e.g. trees and shrubs etc. as they lose their heat into the night in cold conditions, but the detection distance for animals and the like, will not be of any concern, they are still just as hot. 

                                                      BE AWARE.

The industry standard test for sensitivity is done on heated black "targets" at 30 degrees Celsius and using an f1.0 lens.

Many "lesser manufacturers" have the same sensors tested at temperatures HIGHER than industry standard of 30 degrees (40, 50 and even 60 degrees) Celsius to obtain a "better" sensitivity figure than their competitors. 

A HIGHLY DECEPTIVE PROCESS although technically not illegal.

These "better" sensitivity claims are made because they are well aware that users can not actually conduct the tests themselves, and will be highly impressed by the low figures quoted !

Some European manufacturers use 300 mK (28.4 degrees Celsius) which will actually produce a slightly "worse looking" sensitivity figure if you are to be critical.

KELVIN, just to explain - One degree Kelvin is equal to one degree Celsius - they just start at different points.

E.g. 0  degrees C = 273.15 K, and 1 degree C = 274.15 K, both up by one degree, and so on, so you can see from that, in each system one (1) degree is the same as the other. 

Kelvin is the scientific system for measuring absolute zero. 

e.g.  0 Degrees Kelvin = Minus 273.15 degrees Celsius. 

Scientists do not believe you can have a minus temperature. 

1 mK is 1/1000 of a Kelvin. 

So with a sensitivity of say 50 mK for example, you can see temperature differences of 50/1000 or 0.05 of one degree of temperature!

Do NOT believe all the claims made by most suppliers, that you can see through fog, smoke, rain, etc. 

Well, OK, yes you can, but with reduced performance (D.R.I).

Even atmospheric pressure alters the performance capability of thermal imaging (and all other types of NV as well). 

Remember, anything, including foliage, that completely prevents "heat" being "seen" will prevent detection with thermal. 

Any obstruction in the line of sight will prevent detection with ALL optical equipment.  

A real benefit of thermal imaging over other forms of night vision, apart from the far greater range, is that you need NO light at all, visible or near infrared*, and at the same time it is possible to see objects that are hidden in dark shadows even partially obscured by foliage etc.

(As noted above. *near infrared are the infrared wave lengths closer to visible light, which image intensifying and digital devices can detect but thermal devices do not) Thermal devices, other than those used to detect gasses, detect ONLY Far infrared range (8000 - 14000 NM).

     Thermal is superior to all other "night vision" devices in all situations.

Thermal WILL allow you to see into shadows and total darkness.  

Image Intensifying and Digital WILL NOT ! 

Thermal WILL show indications of a potential target amongst bushes, trees etc. 

Image Intensifying and Digital WILL NOT !

                                                ************

The above diagram shows a portion of the electromagnetic spectrum. 

The whole spectrum starts way down below radio frequencies and continues far above X-Ray.

As you can see all the Infrared frequencies that we are involved with, are "same thing" as Radio Waves, Visible light, and upwards, just different frequencies, which in turn governs the wave lengths.

It can be clearly seen by this, that as the frequency increases, the wave length decreases.

(Wave length is measured over one full cycle).

It is interesting to note that one Australian reseller of night vision / thermal devices, claiming to be a major supplier to the Australian Military (???) does not understand. It appeared to be that just after reading the information on my old web site, he made some changes but kept the same text now in bold, which only highlights the fact he still does NOT understand, and obviously did no research on the subject. 

He quotes,  "as the plate heats, the frequency of the energy released decreases", ,...."there will be Thermal IR energy emitted along with frequencies down to the upper red spectrum".... "it will start to glow red (a lower frequency), which we can see with our eyes .." (??)

NO, the frequency INCREASES, (get faster) all the way up to, and past visible light and into X-rays etc. 

Wave length DECREASES. (i.e. gets shorter).

There is so much to learn about this subject, please call and discuss it with us.