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The Truth, the Whole Truth, and Nothing but the Truth ...

Part One

Hello friends. By the time you read this, the holiday season will have passed but as I am writing this it's not here yet. Hope you and yours had a good one,  with some time off somewhere, and a pause to reflect what Christmas really is all about. It's not trees, lights, booze, gifts and time off from work. Rather, all those things are supposed to be in honor of the Son of God who was sent 2000 years ago. Our spiritual beliefs vary, but most of us acknowledge a higher being.

 Our country was founded by men who knew God, and looked to Him  for guidance. Our country and our leaders, unfortunately, have changed since  then, with most looking to themselves rather than God for direction. Are we still One Nation Under God? Or do we think we've gotten so smart since then that we don't need Him anymore? Is our society healthier now than in the earlier days? What do you think?

 Your mission this month, should you decide to accept it, is to examine, in  depth, several issues relating to the application, selection, and use of night  vision equipment. As always, the bottom line in these articles is to help you get the best piece of equipment, at the best price, for the job you need to do. We sometimes are painfully honest in our attempts to do this. Reputable vendors selling quality equipment should take no offense from anything we discuss. Some pukes in the  industry, however, would rather not see you educated. The more you know about what you're buying the fewer opportunities they will have to rip  you off. As always, if you or any member of your force is caught or killed, the sergeant will disavow any knowledge of your action.

 Sometimes it is difficult to get a fair deal when the beancounters have to purchase from the lowest bidder. There are reasons a firm is low  bidder. Usually they are positive reasons (lower overhead, higher  volume, not greedy, etc.). But it's not unheard of for a particular vendor to be cheapest because he has found a way to give you less than  the other vendors. Surveillance equipment is a complex field, and it is not difficult for an unscrupulous vendor to offer something that appears to meet the system specs but which actually is less than the purchasing agency thinks they're getting, and less than the other vendors are offering. There is no such thing as a free lunch.  Investigate carefully and compare precisely what is offered by each  vendor.

 We saw one recently where the low bidder held back the  accessories the manufacturer includes with the piece and charged them as separate line items on the invoice. Of course he was "cheaper" than the rest of us. By the time the using agency finished fighting with the  vendor and finally ended up with what they wanted to get in the first place, they had spent hundreds more than they should have. If the using  agency had a better understanding of what they were trying to buy they  would have eliminated the sneaky vendor from the running. This is one of the reasons it is so important to have the technical types who will  be using the equipment review all bids before an award is made.

 While I'm on the soapbox about price, I'll repeat the words I've said here previously: It's dumb to pay too much, but it's also dumb to pay  too little. If you pay too much, all you've lost is a bit of money. But  if you pay too little, you might lose everything because the thing you  bought doesn't do what you paid for it to do. The small bit extra you pay to assure that you are dealing with a reputable vendor is peanuts  when amortized over the life of the equipment.

 There is no product or service that someone cannot make a little bit  shoddier, or cut some corner, in order to sell a little cheaper. The  people who buy on price only are this man's lawful prey. (These words were penned by somebody famous; I don't remember who.)
Most of us don't have any complaint with our competitors who sell for  less. After all, they know what their product and service is worth ...

 The summation of all the above is: do not buy the cheapest unless you're certain all other factors are equal. Look for value, not lowest price. Make sure the lowest bidder has read your specs carefully and  has covered all of them in his bid. Many agencies who purchase hi tech  equipment need some handholding while they are getting started. This is  the first thing to go when a vendor cuts his prices to rock bottom.
We'll cover a bit more about purchasing night vision later. I'm tired  (pronounce: tarred) of the issue now.
We'll presume at this point that you know enough about night vision to appreciate what it can contribute to your operation. Most decent night vision systems will operate in several modes: handheld, as a weapons sight, as an intensifier in front of a video camera or 35mm film camera. Additional applications might include dash or deck mounting for  piloting a vehicle at night. In order to specify the proper equipment inventory for your particular purpose, it is necessary to understand night vision on a system level. The actual night vision device, the  "intensifier", is only one component of a complete package. Other stuff  must be added to the basic intensifier to make a useful system.

 The drawing shows a typical basic configuration. The particular system  shown is the Dark Invader, but the concept is the same for most manufacturers. Note the intensifier as the heart of the system. Most accessories attach to the intensifier in some way. On the front of the intensifier, some sort of lens is necessary to capture, magnify and  focus whatever it is you are observing. This lens, always where the light enters first, is called the objective lens. This objective lens  is what to change if you want to vary the magnification or field of view that the scope sees. In most night vision systems the objective lens is variable power, providing a zoom capability. A 135mm lens is typical on many units.

 We're not going to crawl too deep into optics here, but we should learn a few things so we know what optional lenses to specify when we order  the night vision system. Overall magnification ratio is determined by  dividing the focal length of the objective lens by that of the  eyepiece. On the typical system we are examining, a 25mm eyepiece is  supplied. The 135mm objective lens divided by the 25mm eyepiece figures out to a 5.4:1 zoom ratio. We change objective lenses rather than eyepieces, so let's look at what changing to a longer objective lens would do. Another typical objective lens is 200mm. With the same 25mm  eyepiece, that would give us a 8:1 zoom ratio. We get orders for 1200mm objectives on occasion, which means the operator requires (envelope, please...) a 48:1 zoom capability.

 A cheaper way to stretch the capability of a single objective lens is to put a 2X multiplier (also referred to as a "doubler") in front of the objective lens. A doubler is about 1/3 the price of a typical  objective lens and, as you guessed, will double the magnification of  the system. A doubler is a small optical part which threads between the  tail end of the objective lens and the front of the intensifier. It can be taken on and off in seconds.

 Don't go crazy with long lenses. Once you get beyond a certain point it becomes difficult to hold the scope steady enough. We find above about 200mm is more than most men can handhold steady enough to get a good image, unless you don't smoke, don't drink booze or coffee, and go to  church a lot. You should automatically think tripod to provide a stable  platform if you need a long lens. By the way, please don't skimp on the tripod. A good, sturdy fluid head tripod will be a joy to use, and has applications for many things other than the night vision. There really isn't much difference in price between a mediocre tripod and a truly fine one. If your agency doesn't already have a tripod, slide down to  your neighborhood camera store and try before you buy.

 Earlier this week I was on a roof playing with a Dark Invader behind a  1200mm lens (actually a small telescope). The unit was mounted on a heavy duty tripod. Although I could count the rivets on a water tower  about a mile away, the vibrations from passing airplanes and truck  traffic were enough to spoil a serious observation effort. I doubt if a  long lens could be used in a vehicle, as the vehicle's suspension would let everything bounce around enough to cause problems.

 Now would be as good a time as any to talk about some ways to save  money on objective lenses. You can buy whatever one you need from the night vision supplier, and it will work very well. They will be  expensive though, and probably there will not be a great variety of them available. Another route you can take is to buy what is called a T  Flange. A T flange threads directly onto the front of the image intensifier, and lets you use the various lenses from a 35mm film  camera setup as objective lenses for the night vision.

 This is nice for  several reasons: one, you possibly already have a heavy duty investment in lenses for the 35mm setup (and maybe even have some exotic lenses), second, your people are probably already familiar with the characteristics of these lenses, and third, if you have to buy lenses you might as well save money and buy ones that can do double duty for  both your 35mm and your night vision system. A typical T flange costs  $75. Note that if you order one of these, you will need to specify what 35mm camera lenses you have (Nikon, Minolta, Yashica, Canon, Pentax,  Olympus, etc.) so your faithful supplier can give you the proper T  flange. They are universal to a point. I have one here that is for a  Yashica. Several different brands of lenses fit it.

 Another option for inexpensive lenses, and one that we recommend, is to get a C mount adapter. This adapter might run you $70. A C mount adapter will let you use the myriad (I like that word...) of inexpensive and very popular CCTV video system lenses as objective lenses. This adapter also threads onto the front of the night vision, and the standard C mount CCTV lenses thread into the adapter. CCTV lenses are available in many nifty configurations, including telephoto, wide angle, pinhole, various disguised lenses, and even fiber optic.

 And should your requirements for the night vision system be rather  exotic, remote control CCTV lenses are readily available which provide  remote adjustments for focus, zoom and iris. By the way, if you're going that elaborate don't overlook remote pan and tilt systems that can move the entire night vision system and associated camera. Control  is usually via wireline, although our firm manufactures a line of remote wireless (radio) control and telephone line control systems.

 Now it's time to talk turkey about the intensifier. See the drawing.  This is the heart of the night vision system. The intensifier is what actually does the light amplification. There's really not much to it. The intensifier consists of a tube (that's right - a tube), usually 3  volts worth of batteries, a switch, a brightness control, a housing and not much else. Later, we'll discuss a few modern enhancements to the basic system that are offered by certain manufacturers. A night vision device consists, in its minimum configuration, of a tube, its  batteries, a housing, and optics in and out. The performance of the entire package is dependent totally on the quality and performance of  the tube. Pay attention to this next section - it's important.

 If you will be purchasing night vision, you must understand the information following or you stand a good chance of being taken  advantage of.

 Intensifier tube performance is a very important factor in evaluating and selecting a night vision device. I will list here some of the many specs to contrast and compare between the various units offered. I will  also explain how to tell which spec is better than another.

 First some soapbox.
Intensifiers are graded based on the tube's demonstrated performance in  a variety of tests conducted by the tube's manufacturer. The grade  assigned determines the quality of the tube, also its price. Note well - it is practically impossible for anyone other than a highly  specialized lab to authenticate claimed specifications. I do not know  of any police agency that genuinely has the capability to perform these tests. Knowing this, it is VERY common for several night vision system  manufacturers to claim unrealistically high performance for their systems.

 At least three regular suppliers of night vision to the law enforcement community greatly exaggerate the performance of their  equipment. If you are buying night vision on competitive bid, and  select the unit based on the vendor's paperwork only, there is an excellent chance you will end up buying a piece from one of these  unscrupulous, but apparently respectable, vendors. Every intensifier  tube is supplied with a data sheet by the manufacturer indicating the  various tests a particular tube has undergone and its performance in  the different areas. Insist that a prospective vendor submit a tube data sheet with each bid. I am certain, now that this has been said in print probably for the first time, that some vendors will start forging tube data sheets. Protect yourself accordingly with a statement to be  signed indicating that the vendor is telling the truth about the  performance of his equipment.

 The only real way to protect yourself is  to require a side by side demo of each piece by the respective vendors. This requirement, unfortunately, will serve to raise prices as vendors  can't afford to fly all over the country to demo a piece that might only make them a few hundred dollars if they get the sale. Also, it is common for a vendor to make up a demo using a super top quality tube even though he is using low spec garbage in his production pieces. I really don't know what else to suggest except to buy from a reputable  vendor, and CHECK several police references. Requiring a one year unconditional warranty against defects in materials and workmanship  will protect you against at least one poor quality system from a well known supplier who wouldn't dare offer a warranty with their garbage.

 Try to deal with a vendor who really understands night vision. Many of  the guys out there selling (brokering) the stuff on competitive bids  literally never have seen a night vision piece. Certain agencies interview each prospective vendor by phone to see how much they really know about the equipment.

 Something else we see on occasion are optimistic groupies who buy a single night vision piece hoping to get rich by selling them. Well, the  facts of life in night vision is that it's a cutthroat market with minimal profit and very high inventory costs. Unless a dealer sells  large quantities he likely can't make enough, selling at competitive pricing, to afford to keep the line. So what happens is some guy buys  one piece, then when he can't sell it anywhere else he blows it out cheap in a competitive bid somewhere just to get some of his "investment" back.

 Of course the purchasing agency will get a unit at a  low price, but if or when they have questions they're out of luck trying to get any help out of this guy. I've personally seen this exact  scenario at least three times recently. Perceptive purchasing agents  require a statement from the prospective vendor certifying that he is a regular dealer for the system offered. Requiring a letter to that  effect from the dealer's manufacturer also would not be a bad idea.

 OK. Time for specs. If you're allowed to have sharp objects, cut this section out and file it in your section's wish list folder for when the  budget finally happens and you can buy one of these goodies.

Specs to compare are:


Diameter of Image Intensifier

Cathode Sensitivity

 White Light Gain

Center Resolution

See the data sheet reprinted here. This is a typical data sheet for a  top quality 25mm tube, and is one from a Dark Invader.

 Many more specs than those above will be listed on a data sheet supplied with a tube, but the ones indicated are the most important.

 Diameter of Image Intensifier - More is better. Measured in millimeters (mm). Intensifier tubes typically come in two sizes: 18mm and 25mm. The  25mm is the one to choose unless you have an extremely specialized  application requiring a smaller tube (like night vision goggles, which  must, for reasons of size, use an 18mm tube). The greater the diameter the bigger, and better, the image. Sort of like the difference between a tiny TV screen and a large one. The difference between 18mm and 25mm is greater than it seems. Going by area (Pi times the radius squared), we see that the area of an 18mm tube is 254mm. The area of a 25mm tube is 491mm, or almost two times as much. There are plenty of both 18mm and 25mm systems out there.

 Cathode Sensitivity - More is better. Measured in microamps per lumen (uA/Lu). Also referred to as "Photocathode Response". 350 uA/Lu or more is excellent. Less than about 250 is unacceptable. Photocathode  sensitivity is the ability of an image intensifier to gather light at very low light levels. This is a rather critical spec.

 White Light Gain - More is better (I'm starting to sound like George  Orwell...). No units of measurement here, just numbers. This is, rather obviously, the factor by which the night vision device will amplify the  existing light it so faithfully gathers for you. This spec is the one most often quoted, and exaggerated. Gain is important, but look at the  other areas of performance also.

 Do not accept less than 50,000, and 60,000 to 70,000 is commendable. I have evaluated pieces from certain  manufacturers whose published gain was 70,000. My calibrated eyeball suspects that a realistic estimate would be maybe 20,000. If you had never seen anything else to compare it to, you would have been impressed. If you had, you would have been disgusted.  Center Resolution - More is better. Measured in line pairs per  millimeter (lp/mm). Also frequently exaggerated. This spec is very important if you will be filming or videotaping whatever dastardly deeds you observe through your night vision. More resolution means a more detailed image, and well could mean the difference between  positive facial ID and something the State's Attorney won't accept.

 Hold out for 34 - 36 lp/mm. Note that this is line pairs per millimeter of the active tube face. This is another reason to go for a 25mm tube  vice an 18mm. In a quality 25mm tube, this will equal 36 line pairs (72 lines) per millimeter times 25, or very roughly 1800 lines. The more lines the better the picture. As a reference, standard home TV is maybe  400 lines in a good set. Extremely high definition medical imaging  systems might be around 800 lines. You can see that the resolution of a  very good tube will greatly exceed anything you can hang behind the night vision system to record the image.

 The industry has developed standard references to be used in evaluating image intensifier tubes. They are, in ascending order of quality:  Commercial Grade, Mil Spec, and Hand Select. Refer to the table below  for specifics:





Cathode Sensitivity

 Below 239

240 - 325

Above 325

 White Light Gain

Below 30,000

30,000 - 50,000



20 - 28

28 - 36

36 - 40

You could be completely safe in specifying a night vision system by  requiring that any system offered meet hand select specs for all three  criteria. If this upsets any manufacturer it means his piece is not up to the quality of others on the market. Speaking of which, there are several manufacturers who do legitimately offer a night vision package to law enforcement which meets all the above specs and is, in most cases, lower priced than lesser units. Call our office if you want some names. I'm not allowed to mention them in print.

 Again, be aware than vendors can claim anything they want for their particular piece. Tube data sheet, guarantee and/or demo.

 We're about out of space for this issue so apparently this will be a  two, or maybe even three, part series. Next time we'll finish up on the configuration of the night vision system and get into eyepieces, relay lenses, film and video cameras attached to these things, 35mm film processing details, and much more. We'll also examine in some detail what all the various accessories are for that are offered by the manufacturers. We'll cover how to initially set up and operate the system and how to use it in typical surveillance scenarios.

 Is there anything else relating to night vision that you'd like to see  here? Please let me or the magazine know so it can happen.

 By the way, if anyone has any experience using a Dark Invader in front  of a 16mm movie camera, please contact either our office or George  Andrews of the Peoria County (Illinois) Sheriff's Department. Our  number is (410) 879-4035, and George's number is (309) 697-7826.

 The 1989 Secret Service PPC regionals are scheduled for 5, 6, and 7 May 1989 at the usual location in Beltsville, Maryland. Contact me for details if you're interested in participating or exhibiting there. Participation is restricted to law enforcement. This event is always enjoyable and generally attracts the heavies in the industry who don't often show their faces elsewhere. Their facility is beautiful and the  Secret Service crowd are very gracious hosts. Last year had beautiful weather (certain of the exhibits were outdoors), free gourmet ice cream  and sodas all week, superb catered meals and golf cart shuttle service around the facility. We will be in our usual spot in the lower classroom building. Please look us up and introduce yourself.

 There's at least a few turtles out there. See you next month.

 Copyright (C) December 1988 by Steve Uhrig, SWS Security

"Please note: At the time these articles were written, SWS distributed the Dark Invader line of night vision equipment, manufactured by B. E. Meyers Company. We no longer recommend this brand of equipment or this company. Please see our links page for a link to another night vision supplier who we recommend."