Looking for info on the L42 L1A1 scope turrets

If you think the British engraving is convoluted you should see the early production REL Mk.1 !!!
The engraving runs 360 degree around the tube with some info on the top, some at 3 o'clock, some at 6 o'clock, etc.
But, we learned to how to make world class optical glass in less than 6 months.
We were casting billets of optical glass that was second to none but we did not have bombs dropping on our head either.
Our problem was with sealing the scopes and I have had the opportunity to open a number of early REL scopes that still had the soldered over screws.
The seals were oiled cotton twine....Nothing else.
I know it is used on valve packing and Vickers guns but not sure it is kosher for a scope adjustment movement.
The saga of soldering the mounts to the action was also a real bone of contention, as Canada did not solder the pads and there were copious letters back and forth between the UK and Canada on that subject.

I would slightly ........, no vehemently, disagree about REL optical glass Warren, especially with regards REL No32's. There was a soecific instruction called a 'Miscelaneous Instruction Tels,Searchlights and Instrument EMER relating to any Canadian REL telescopes that are in UK military service. To the effect that due to the non interchangeability of the lens optical patters, it may be necessary to replace the lenses as a set with UK production.

To illustrate the point, have a look at various REL Mk1's and 2's. Ocular lens sets with double sprung spacers in order to match the optical light path to focus the graticle. I've got one in front of me now. If the lenses don't match, just replace them from a known matching set from a No42 or 53.

Sorry to disagree Warren but while the glass grinding might be perfect (it is.....) the glass spec was not, hence the refractive index per lens (and there's 4x lenses per ocular set) was not to the spec. Easy to illustrate using a spotlight and a black board

I'm not sure that REL No32's were any worse than UK production regarding waterproofing. Some UK's were good while others were poor

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Originally Posted by Warren

If you think the British engraving is convoluted you should see the early production REL Mk.1 !!!
The engraving runs 360 degree around the tube with some info on the top, some at 3 o'clock, some at 6 o'clock, etc.
But, we learned to how to make world class optical glass in less than 6 months.
We were casting billets of optical glass that was second to none but we did not have bombs dropping on our head either.
Our problem was with sealing the scopes and I have had the opportunity to open a number of early REL scopes that still had the soldered over screws.
The seals were oiled cotton twine....Nothing else.
I know it is used on valve packing and Vickers guns but not sure it is kosher for a scope adjustment movement.
The saga of soldering the mounts to the action was also a real bone of contention, as Canada did not solder the pads and there were copious letters back and forth between the UK and Canada on that subject.

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Are those features ever seen on any other No.32 Mk.I's? Not that I've seen apart or taken apart; in fact was there any spec. for water or weather-proofing the non-R.E.L. Mk.I. scopes? No evidence of same that I've noticed.

Sounds like R.E.L./S.A.L. were pro-actively looking for ways to improve the design, rather than slavishly copying what was provided; a policy that is evident throughout their production - though of course they soon realized they could design better and did: the C67, Telescopes, Observing, Snipers & Stand, Monte Carlo stock for the No4(T) etc.

Can't speak to the quality of R.E.L.s glass compared to UK production, but looked through many R.E.L. and UK produced No.42s and the light transmission of the R.E.L's was clearly and considerably better in almost all cases. Perhaps a bit more spherical distortion at the edge of the f.o.v. though?

As Peter mentioned the curvature of the ocular lens doublets is different from U.K. production - ' don't know why, but commonality of production was reportedly an issue R.E.L/S.A.L. also tried to put into effect where possible.

The difference in curvature of the lenses and spacing between them is due to the different refractive index - which will affect the light convergence point - of the flint and crown glass used. Hence the need to extend the space between the ocular lenses. Not just the oculars, but the erector cell lenses too. In short, the glass used was not to the specification set. But, that said, by adjusting the focal layout of the lenses they produced, they achieved the aim with a hint of outer spherical distortion.

That said, again..... No good trying to replace a, say, cracked REL ocular or erector with a UK lens. From my limited experience once again of having fixed one or two, best start again and use a UK ocular and erector set throughout. That's why you should ALWAYS have a spare No42 or 53 handy.

Incidentally, waterproofing Mk1 and 2 turrets is absolute simplicity itself. You machine a radiused half recess into the lower edge of the thumbscrew/scale drum and a corresponding half recess into the index plate. Insert a suitable diameter x 1mm thickness neporene O ring (cheap per 100!), bit of rubber or silicon grease and that's it sealed at its weak point. EXACTLY as per the W rated No32 Mk3's and L1A1's

I'll second that. One of the most useful pieces of advice Peter ever gave me, when I started having a go at repairing some tatty scopes of my own, was to stick to using complete lens sets. You know that these have been on the optical bench & are matched.

It's not always possible, but if you can manage to turn up a nice No42 or No53 with good lenses made by the same manufacturer as the No32 you're rebuilding, the lenses (as a rule of thumb) will generally fit into the tube without too many dramas. I have several Kershaw No53's I've stashed away for using on a couple of needy AK&S No32 Mk3's........& likewise HBMCo No42's to restore HBMCo No32 Mk1's.......

Of course, you don't always have the luxury of picking & choosing the make of No42 that turns up...........unless you have 450 of them. I wonder, does the gentleman concerned still intend to convert them all into No32's? I would have thought the appearance of relatively inexpensive copies from the Far East would have made that financially unfeasible, if it ever was.

Another turret for the survey, and serial number info in case it's useful.

Sorry to disagree Warren but while the glass grinding might be perfect (it is.....) the glass spec was not, hence the refractive index per lens (and there's 4x lenses per ocular set) was not to the spec. Easy to illustrate using a spotlight and a black board


Please demonstrate this as I would love to see it, probably along with a number of others...
Of course you cannot mix Brit and Cdn lenses that is a give. BUT" sometimes ya get lucky" and get a decent match.
Flint glass, crown glass and the Canadian Balsam used as the glue all have a slightly different refractive index, batch to batch.
That is a given. When originally making the scopes the maker had a lot of choice in assembling matched couplets and the use of a focimeter/lensometer.
I am waiting with baited breath for the lens demo with the flashlight and blackboard as I know several others will be as well.
Perhaps a short video is in order.
The optical engineer who helps me on occasion and I know he would probably be interested as well.
I have some great info from him that some of which I cannot understand and I will send it to you and I am sure you can help us all by an explanation of it, as you taught it.
Anything I can learn on the subject of the theory of simple and complex lenses is more than welcome. The mathematics and forumuli just kill me. I even built an optical bench to work at it.
The mechanical end is rather straight forward, but lens theory is a real bald spot scratchier...for those of us who are folically efficient. And, for us more mature guys.
Many of us who repair the No. 32 keep in touch with each other and share parts back and forth. Even with the exorbitant price of postage, now we manage.
Appreciate the offer of the blackboard tutorial and as most mobile phones have video clip of up to 30 seconds and more it will be a no brainer to post it here.
Hopefully, without overstepping any bounds here, if someone needs No.32 parts just ask, I just might have it.

Ignore reference to a torch - I will try to use a laser for simplicity.

Time to yawn now and nod off for a few minutes........
But back to ocular lenses. You'd think that with modern plastics, like spectacles, you'd think that you could grind or even cast new lenses from optical grade plastics. Someone had tried it, partially successfully too and gave me a set to bench test. Alas, each doublet was cast/machined as a single piece. Without the benefit of the different refractive index qualities of very hard flint flat/concave lens (the flat OUTER lens, -that's why it cracks/chips sooooooo easily) and softer crown, (the inner double convex), you loose the ability to focus on the grat and eventually the image within the distance within the telescope. (that's why we've got prismatic binos)

I did get the optical plasticised lenses to work successfully but only by inserting ONE as the internal lens in the ocular lens train while extending the distance between the lenses. For some reason that I never quite understood, I couldn't get the ocular train to work in the reverse order.

It is for the same reason that later Mk3 ocular lens sets using the plossl optical system have slightly convex outer surfaces instead of flat.
And the same reason why later, the most forward of the erector lens forward facing surface (we call it the 'screen' lens because it acts as the image screen) is very slightly convex instead of FLAT.

Here's a word of advice about erector cells. I'm sure everyone knows this so go back to sleep......
the rear lens is DOUBLE CONVEX. The most pronounced convex surface must face forward towards the graticle - AWAY from the stop-down shield
The screen lens is a PLAIN and CONVEX lens. BUT NOT ALWAYS on later production. In these cases, the most pronounced convex surfaces must face each other, towards the spacer.

Stay awake at the back of the class..........
HOW CAN I TELL WHICH convex surfaces are greater or smaller without an optical radius gauge. That's easy............ Get a dark shallow dish - a saucer is perfect and JUST cover the bottom with water. just a few thou deep will do Place the lens in.
On a flat surface, when viewed from directly above, the water will show over the whole lens
On a convex surface with a LARGE radius, the water will show over a small area at the centre
On a convex surface with a SMALL radius, the water will show over a large area at the centre. The two greater curvatures are to meet. The lens with the flattest curvature will act as the screen. So assemble accordingly.

There is another method by using the size of the reflection of a light but let's keep it simple

Just use a clock dial lens gauge...
Problem solved
You can pick up used ones for a 5'ver on Ebay
A perfectly flat or plano lens surface is almost impossible to manufacture.
I'll post a picture of one of mine later today.

---------- Post added at 11:28 AM ---------- Previous post was at 11:24 AM ----------

Also a big thanks for the pictures of the turrets to those that sent them to my email addie and as a PM.
It is looking about 50/50 on screws and no screws.
I just do not feel comfortable without the grub screws but if it works without ...why not.
It sure saves me time and trouble in drilling, tapping and installing a 10 BA grub screw.
I just (personally) think it is mickey mouse and was the reason I thought the conversion was done with by an outside contractor: bid low and cut corners...