• The WEAPONSIGHT, IMAGE INTENSIFIED, L1 series - Part 2 (by Peter Laidler)

    The following article is published with the kind permission of Advisory Panel Member, Mr. Peter Laidler. On behalf of MILSURPS.COM members, we'd like to publicly thank him for his support of this forum, as well the broader Lee Enfield collector community in general.

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    (Part 2)
    (Or a bit of heavy reading for the holidays..........)
    By Captain Mainwaring
    (a.k.a. Peter Laidler)

    Portrait of the WEAPON SIGHT, Image Intensified, L1A7, the subject of this article.

    (Click PIC to Enlarge)

    Before I go on a bit, someone commented about the name ‘IW as in individual weaponsight’ being a bit of a puzzler. We’ll yes ….., it is really but it doesn’t mean that at all. It actually stands for Image Intensified Weaponsight – IIW but the initials just stuck and the name Individual Weaponsight just followed on. There aren’t many of you who will have this kit but it is available if you look hard plus it’s an important part of the L42 rifle kit. Don’t forget that Brian Dick at BDL Ltd. (click here), in South Carolina, USA. has the booklets so get them while you can. Sorry if advertising isn’t allowed but being cheap, I don’t expect it’ll ruffle too many feathers.

    The two little handbooks. The blue training guide and the buff user handbook. Both available in reprint format from Brian Dick at BDL Ltd. (click here), in South Carolina, USA.

    (Click PIC to Enlarge)

    Where were we….. Oh yes. There’s a lot of mystery surrounding the night sight but I’ll let you into a secret. The vision unit really consists of three (or four if it’s a sight) sections.

    There’s the front bit that consists of the OG or Objective glass. Behind this is a little lens cell that moves very slightly backwards and forwards, via a little thumb-wheel on the left hand side of the casing (yes, that’s it, the knurled wheel thingy…..) that allows you to focus from about 15 metres out to infinity. And behind this, in the focal plane of the object glass is the moving or fixed graticle …..or being technical, the reticle if it’s etched on a glass plate. It’s these features that make these image intensifiers VERY expensive and take them out of the realms of being just ‘night vision’ to being ‘night sights’ and unlawful in some Countries. This part is simplicity itself to remove by unscrewing the 8x allen bolts from around the front housing.

    The mid section showing the knurled focusing thumbscrew, the inverter housing and cap plus the on-off switch. In truth, the switch was a bit flimsy and not really man enough for the job. But protected by the shield and easy to change if damaged, it just about managed. But give a flimsy bit of kit like this switch to a cold, wet and hungry soldier was a bit, well..........!

    (Click PIC to Enlarge)

    The second bit, behind the objective focusing and reticle stuff is ‘THE TUBE’. It’s this electronic or optro-electronic or optronic for short ‘TUBE’ that is the magic part of the whole system and it’s only this that will cause you any problems. This converts the picture that it sees from the OG lens and reticle into a green image so that the bit behind it can pick it up, focus it and make it into a viewable picture that your eye can see. You’re right….., that’s as far as I’m going to go about the tube, simply because what I know about the internal workings of the tube can be written an the back of a postage stamp with a biro and there’d STILL be room for the lords prayer!

    However, I’ll tell you what I do know. That they are extremely light sensitive, even when the power is switched off. I’ll explain what I mean. I saw one that had been left with the front cover flipped off after night observation in the border bandit country of xxxxxxxx. And as the mist covered half sun came up the following morning, it tracked the suns path which burned a distinct arc across the phosphoric plates of the tube. Yes, it destroyed it. I know that you’re going to comment that ‘…well the ones I’ve seen have a shut-down mechanism that operates in milliseconds’. Yes, they do, but the shut down mechanism can’t recognize a gradual build up of damaging light. The tubes (on the L1 - IIW sights that I understand….) are USE sensitive and not TIME sensitive meaning that they become worn out or old through use and not age. So you could have a 4 year old sight that’s virtually useless simply because it’s been in use constantly night after night for years while another 10 year old sight that’s had little use will be as fresh as the day it was made.

    The very heart of night vision. The electronic TUBE. Well, how did we photograph it if it’s just soooo light sensitive? Easy, we taped over the ends after taking it out of its storage box in the darkroom.

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    As a matter of interest, if you are tempted to strip your sight, then I have been advised that if you use a dark-room, and direct a 15w bulb towards the ceiling and work in this subdued light (you’ll quickly get used to it……) then that won’t cause any harm or damage to an unprotected tube. And here’s another thing. At the end of this, I’ll give you a list of all the neoprene sealing rings applicable to this sight. They are readily available from any bearing or seal suppliers under these international part/type numbers. The front and rear plate of the tube should be crystal clean, wipe with clean methylated spirit on a cotton bud if you must use anything. When you close up your sight ALWAYS use new seals, ALWAYS, ALWAYS, just smeared with a dob of rubber grease or coppa slip but NOT mineral grease

    Associated with the tube is the battery power source, a switch and if you’ve got a later one, the ABC dimmer unit. There’s no mystery to this either. The battery and switch can easily be tested with a multimeter and they either work or they don’t! Faulty tubes have one distinct giveaway in that they’re always speckly….., a bit like a snowstorm howling across the screen. The degree of tiredness is relative to the severity of the snowstorm but clearly, always check the battery first. The good news is that the tube from the British IIW/ SS20/L1 sight is the same as the US equivalent sight. The tubes are still current, now made by EEV (part of the GEC group) of Cheltenham, Essex as type P-8079-HP. Here are a few other numbers to quote to help your quest along. K/EEV R9224 and you could quote the old MoD number of 5960-99-038-2689 too.

    Just in behind the tube is the last bit, called the ocular lens assembly and this has at the rear an eyepiece shutter that opens when you push your eye onto it and flaps shut when you remove it. I’ll tell you why. If the shutter didn’t snap shut, then as soon as you removed the sight from your eye, your face will be illuminated by a big green rosy glow from the rear of the ocular lens. And while this nice warm rosy green glow might be miniscule in the real world, to a night vision equipped observer on the other side looking at you, it looks like a huge glowing torch shining on your face……………….. And it is for this reason why the Armed Forces don’t bother with Infra Red illuminators. Our night vision is passive. If YOU can pick up the infra red illuminator of your own AND his night vision, then guess what the enemy observer can pick up too………, yep, got it in one and as sure as god made little green apples, mortars will follow shortly.

    The ocular end and the eye shutter. The importance of this shutter is explained within the text.

    The ocular lens assembly. This simply transfers to the eye a viewable picture of the green intensified image. Simple really.

    (Click PIC to Enlarge)

    Removing the ocular lens assembly is a little more, but not TOO difficult. Between the sight casing and the ocular lens assembly you’ll see a threaded locking ring. You’ll have to unscrew this with a set of special or home made adjustable pin pliers. Unscrew it and the ocular will follow. Then you’ll see the rear end of and rear screen of the all important tube. Once again, if it needs cleaning, then just a wipe with pure methylated spirit on a cotton bud will suffice. Like most telescopes….., which this is, the focus of the image is carried out by easily adjusting the focal distance of the ocular lens from the image on the rear screen.

    The OG lens cap. MOST important bit of kit. There were several different types and this is the latest. Note the small pinhole in the centre. There was sufficient light allowed to pass into the tube to allow the sight to operate and allow it to be zeroed in daylight. But written around the edge in large letters were the words ‘DO NOT REMOVE IN DAYLIGHT’

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    What else is there to tell you? Not a lot really. You can do most things with care. But if you’re hell bent on removing the tube, then it can only be removed through the rear. First remove the inverter housing cover, unscrew the inverter from the tube, then carefully withdraw the tube through the rear. It’s as simple as that.

    If you’re not game and wish to take your IIW sight to one of the specialists, then might I strongly suggest that you take with you a set of the seals and tell him to renew them PLUS a copy of the user handbook so while it’s physically different to what he’s used to dealing with, he’ll quickly understand it.

    Right, here’s that all important list of ‘O’ rings and seals if you must…..

    Battery cover 200-030-4470 or 4490
    Switch seal PP45/7
    Switch cover screw seals x4 400-001-4490-041
    OG main lens seal 200-040-4470 or 4490
    Focusing adjuster shaft 200-012-4470 or 4490
    Field lens seal 200-025-4470 or 4490
    OG casing to main casing* 200-038-4470 or 4490
    Zeroing shaft seals x2 200-008-4470 or 4490
    Main ocular lens seal 200-034-4470 or 4490
    Ocular inner housing seal 200-033-4470 or 4490
    Insulator bushing seal* 200-038-4470 or 4490

    There are two I haven’t mentioned and they’re the flat gasket type seals for the ON-OFF switch cover plate and the inverter plate that you can easily cut from inner tube.

    4470 or 4490 is alternative material hardness

    Some of the most important seals used in the rebuilding of needy L1A7 night sights. Never but NEVER use the old seals again and if you have a sight, please keep a set as spares, especially the battery cover. Stray light and dust are the arch enemy of night vision kit. They are available from all good engineering suppliers using the code numbers supplied.

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    If there is a demand for the seals, I’ll see if I can’t get a few sets made up for the cost plus post. They won’t be more than a few ££’s. Can’t get any fairer than that can I?

    But I could be wrong.............

    Copyright ©2006 - 2009 by Peter Laidler and MILSURPS.COM

    Collector's Comments and Feedback:

    1. In addition to being a trained and highly experienced military "Armourer", Peter Laidler has authored two excellent books about the No.4(T) sniper rifles and their No.32 scopes. They are titled "An Armourer's Perspective: .303 No.4(T) Sniper Rifle", which he co-authored with Ian Skennerton and his own dedicated work, "Telescope Sighting No.32".

    If you're really interested in some in-depth learning about the No.4(T) sniper rifles and the No.32 series of scopes, their history, evolution, repair and adjustments for shooting, I'd highly recommend those two books, which are pictured below.
    ....... (Feedback by "Badger")

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    2. Here are a set of pics showing the PVS-1 night scope mounted on my L42A1. Note the picture of the batteries that came with it and specifically the date on them. It's 1993 and they still work. I had to throw a couple out that were dated back in the 70's. I hope I can find replacements in the future. Also Notice that they are 7.0v instead of 6.5v. While the batteries shown in the picture are marked 7 volts, a 6.5 volt battery is identical. This is because each individual cell in the battery produces 2.12 volts. These particular batteries are 3 cell units, therefore 3 x 2.12 = 6.36, if the units in question were four cell units they would be '8 volt' (actually 8.48 volt). The 7 volt nomenclature is unlikely to be correct, although a six volt battery fresh off the production line will show 7.xx volts. More important for anyone who owns such a device is the amp hour rating of the battery, as this will have a greater effect on the run time of the device. Please note that it's highly illegal to throw them in the garbage or dispose of them anywhere but a hazardous waste facility. ...... (Feedback and pics provided courtesy of "Ricoim")

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    3. The IWS weapon sight was a 3.75x magnification first generation British weapon sight, based on a triple staged intensifier tube with Automatic brightness control, in fact it is the same tube that was used in the later versions of the US PVS-2 system. It was designed to be mounted on the L42a1 rifle, Carl Gustav rocket launcher, L1a1 rifle, and M16 rifle and the L7 GMPG.

    It was powered by two 6.75 volt mercury batteries providing about 70-100 hours of power for the unit. It is superior to the PVS-2 type system in that it has an internally adjustable reticle (graticule) that lies in the front focal plane of the weapon each click is ½ Mil of adjustment (1mil =~3.4 MOA). In contrast the PVS-2 had a fixed reticle and could only be used with externally adjustable mounts designed for specific weapons such as the M16 or M14. The effective range for the unit is 300m under starlight conditions, improving to 500m in higher ambient light conditions (moonlight) which is similar to ranges for the PVS-2 unit of the same vintage. During the Vietnam war PVS-2 equipped XM-21 sniper rifles regularly scored kills out to 300-500m. The sight comes equipped with a front lens cap that incorporates a neutral density filter to be used during daylight to zero the unit, it can be set to three settings.

    The reticle of the unit:

    Points a and b on the reticule correspond to 200m and 500m respectively for 7.62mm weapons. The cross above point a is used to boresight the Carl Gustav anti-tank weapon. Points b,c,d,e,f correspond to 100, 200, 300, 400, 500m when using the Carl Gustav Lines G,H,I correspond to leads of 7.5 mils, 15 mils, and 30 mils respectively. These were typically employed when using the Carl Gustav, but could also be employed as windage holds with the 7.62mm rifles.

    Zeroing the Unit:

    Place unit in stable rest and sight the rifle at 200m using iron sights. While viewing the target through the eyepiece adjust the filter and focusing knob to obtain a clear image. Adjust the reticle screws so that point a on the reticle corresponds to the target. If possible verify the zero by firing a group. Adjust if necessary.
    ...... (Feedback by "harlikwin")

    IWS Reticle

    (Click PIC to Enlarge)

    Note: The opinions expressed herein or statements made in this article are solely those of the author, and do not necessarily reflect the views of the Military Surplus Collectors Forums, or the ownership and moderation group of this site. MILSURPS.COM accepts no legal liability or responsibility for any claims made or opinions expressed herein. Also, please note that neither the author nor MILSURPS.COM recommends that any member of these forums, or a reader of this article, try this type of experimentation without the proper knowledge, equipment and training.
    This article was originally published in forum thread: The WEAPONSIGHT, IMAGE INTENSIFIED, L1 series - Part 2 (by Peter Laidler) started by Badger View original post
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