make thisSNOOPERSCOPE

and see intotal darkness

By Harold Pallat i

PICTURED above is only one of the pos-sible applications of the modified war-

time sniperscope. This unit, called asnooperscope, is an enlarged version of theinstrument used by GI riflemen to enableaccurate fire power in total darkness. Whenthe infrared light source is turned on, theuser, by employing the special eyepiece,can see in the area covered by the light,although to the naked eye total darknessstill prevails,

A number of more practical applicationshave been developed with the snooperscopebecause of its ability to peer through anyopaque material that passes infrared rays.Crime detection laboratories are now usingsimilar equipment for reading through cer-tain types of material. Since the infraredreflection of pigments in paints and inks isdifferent from that of white light, it is pos-sible to detect forged paintings and checksby the way the colors appear. You candemonstrate this by writing a message withIndia ink and then painting over it with acoat of ordinary fountain pen ink. Your eyewill only see the blackened spot but thesnooperscope will peer through the top

Mechanix Illustrated

layer of ink and reveal the writing just asclearly as if there were no top coating. Thistype of inspection can be made photo-graphically if infrared film is used in thecamera. The electronic method permitsinstantaneous examination which often isa great convenience.

As you might have thought, there areseveral photographic applications. Usingthis device, you can take photographs withno visible light source. (For instructionson this type of work, see Shoot 'Em In TheDark, January, 1951, MI, pgs. 148-149.)One of the handiest uses is using the snoop-erscope as a darkroom viewer. Difficult op-erations that have to be carried out in totaldarkness can now be viewed clearlythroughout the process. If you run intotrouble loading film tanks you will appre-ciate a viewer when the film becomessnarled. A test for fogging should be madebefore the viewer is used. Within the nextfew years every modern darkroom may beequipped with infrared viewers.

In scientific laboratories a modified unitsuch as this is used to study the behaviourof small nocturnal animals in total dark-

ness. A converter tube has been used witha microscope to study bacteriological andbotanical specimens under infrared rays.Certain large molecules may now be ex-amined in a different way, since they be-come transparent under infrared light.

Military uses are obvious. The sniper-scope has already been mentioned. TheGermans used infrared-equipped tanksand trucks for driving during blackouts.Under these conditions they could travelalmost as fast as during the day. Carsequipped with a snooperscope would havethe advantage during fog. Certain types offog are transparent to infrared (depend-ing on the particle sizes) and during suchweather increased safety of the road couldbe obtained. The experimenter is cautionedabout building a unit for this purpose, asvery good lenses are required as well aspowerful headlights. Such specialized con-struction is likely to prove difficult anddriving with makeshift equipment wouldbe dangerous.

In the actual construction of your snoop-erscope, your best tube would be one ofseveral British models, which are available

August, 1951 99

on the surplus market. Two of these aretype CRI 143 and CV 147. For operation atthe highest voltages, the tubes should becarefully selected. Other electronic partsrequired are a 4,000 to 6,000-volt low cur-rent power supply (less than one milliam-pere), a light source and two niters.

For indoor operation a 4,000 to 5,000 voltneon sign transformer operates the tubesatisfactorily. Two 1-megohm resistors areused, one in series with each lead, to limitthe current. Rectification is not necessaryunless the objects are in motion (objectsin motion cause a stroboscopic effect whenAC is employed.

For portable use either indoors or out-doors a handy-sized power supply may beconstructed that operates off three standardflashlight cells. For continuous operationleave the power supply on as long as re-quired. Very long battery life can be ob-tained by switching on the power supplyonly momentarily to charge the condenser.The condenser will then store this energyand continue to operate the tube for sometime after the unit is turned off. Place asmall piece of rubber tubing over toggleswitch handle to help eliminate chargepickup.

The high voltage is supplied by a modelairplane ignition transformer with a vi-brator to interrupt the primary current.These transformers are available on themarket with the vibrator already built in.Only two wires need be attached for op-eration. You can make up your own vi-brator coil arrangement by using the partsof an old buzzer or bell. Some types of buz-zers can simply be connected in series withthe primary of the transformer. Try yours

to see if this is possible (1-1/2 volt buzzers).Caution: Avoid contact; these voltagesare high and while not dangerous, cangive you a rather uncomfortable shock.

Construction oj the snooperscope: Theimage converter tube is mounted in a plas-tic drinking cup 3-1/2in. high by 2-1/2in. indiameter. The optical system required de-pends upon your intended use. We used asmall tripod type magnifier lens of 10 power(1 in. focal length) for the front lens andobjects from three inches to one and a halffeet can be focused. There is no reason whya greater range cannot be had with this lensby moving it closer or farther away fromthe tube.

After selecting the lens system mount itin a hole cut into the bottom of the cup. Ajeweler's saw or coping saw is ideal for cut-ting the hole. Paint the inside of the cupwith black paint. Black airplane dopeworks fine. No light other than that fromthe lens must be permitted to hit the tube.Place an infrared filter between tube andlens to reduce effects of stray white light.

The image converter tube is insertedwith the graphite side toward the frontlens and the metal ring toward the mouthof the cup. A thin flexible lead from themetal ring connects to the positive side ofthe power supply. Some tubes were manu-factured without this lead, in which case apiece of spring metal pressed against themetal ring will work just as well. The frontend of the tube has a graphite ring aroundit. This is the end where the infrared imageis to be focused. The graphite coating is thecathode or negative lead. Connect this leadto the B minus side of the power supply. Apiece of spring [Continued on page 150]

100 Mechanix Illustrated

Top view of simplified power supply for portableuse. Cells are the ordinary flashlight type. The en-tire unit is mounted on a 3/4-in. plywood baseboard.

The snooperscope itself. For indoor use a smallneon sign transformer (right) may be used topower the infrared tube within the plastic cup.

ISO

Snooperscope[Continued from page 100]

brass or even the flat sheet metal carefullyremoved from a tin can should be formedwith the fingers so it fits snugly around thecathode terminal.

The rear viewing lens is optional as it isonly required if you wish to view the imagesclosely with the eye. It should have aboutthree power and a focal length between 2-1/2and 4 in. This lens is mounted and cementedto a piece of plastic or wood. The materialshould be opaque and have good insulatingqualities. The handle is a plastic bicycle han-dlebar grip which is cemented over a holedrilled into the side of the drinking cup forthe high voltage leads. The lead wire can bethe plastic type of zip cord, over which isplaced plastic insulating tubing.

Light source: The main limit to the view-ing distance is the power and type of lightsource. Greater intensity means greater dis-tance. For the direct viewing of glowingobjects this imposes little difficulty. Such ob-jects as the moon and extra bright stars maybe viewed directly. A small flashlight with aplastic filter may be detected at quite a dis-tance. Reflected light from objects requiresthe use of heat lamps, photofloods or standard100 to 300-watt lamps to illuminate them. Ofcourse these lights are filtered so that novisible light is seen. The light source shownon page 100 consists of a 300 watt sealed beamoutdoor type floodlight (115 volt), a glasstype infrared filter and a 10x10 in. recessedlighting box.

Outdoor applications involving greaterdistances require a bulb with a sharply fo-cused reflector. Gold-plated reflectors givevery good results. The sniperscope used a 30watt, 6 volt bulb similar to the type used inauto headlights. This was operated on a smallrechargeable storage battery. Good substi-tutes are auto spotlights of the sealed beamtype such as Westinghouse type 4535 or theGeneral Electric 4524. Standard type flash-lights with small dry cells will not provideample infrared for viewing by reflection.Never point your snooperscope at extremelybright light sources like the sun. Damage tothe tube may result.

Infrared filters: Experimental filters can bemade by sandwiching several layers of darkred and blue cellophane between two sheetsof clear plastic. Both plastic and glass typesare available from photographic and scientificsupply houses. The latter type is to be usedwhenever heat is involved. Infrared filterscut out all or most of the visible radiation andallow the heat rays to pass through unob-

[Continued on page 152]

August, 1951

Snooperscope[Continued from page 150]

structed. Since a tungsten lamp producesmuch more infrared than it does visible light,the action of a filter reduces its strength onlyslightly, while to our eyes it now becomestotal black. Don't forget that it is possibleto overheat even glass filters, so light sourcesshould not be left on longer than necessary. •

August, 1951