Focal length looks to be 400mm but being imperial I would say the focal length is 16 inchs
Crazy 
That’s a great find on the mirror and being able to put it to good use.
1940
C.A.Parsons &Co Ltd
90/408 =? 90 cm diameter and 408mm focal
OB 11624 =? serial number
from wiki pedi
The Company was founded by Charles Algernon Parsons in 1889 to produce steam turbines, his own invention. At the beginning of the 20th century, the company was producing up to 50 turbines a year at its factory in Heaton in Newcastle upon Tyne.
C. A. Parsons and Company was a British engineering firm which was once one of the largest employers on Tyneside. The company became Reyrolle Parsons in 1968, merged with Clarke Chapman to form Northern Engineering Industries in 1977, became part of Rolls-Royce plc in 1989, and still survives today as a division of Siemens.
He also designed special Optics for searchlights:
http://houseofdavid.ca/parsons.htm#searchlight
Some of those photo’s look like some sort of Alien arrival lol! mad……
Kennybobby,
Thanks, saves me doing the search.
90/408
Im not sure they would have been using a metric system then. Usually with the metric system units are not mixed. It would be 90/40.8cm or 900/408mm. I thought it may have something to do with aperture
This was a 5min build to see if the saucepan lid was parabolic seems it kinda is. After reading this on CP fourm it has got me wondering, like a big wok maybe not custom made but will it focus to a hot spot. Anyone could build a mutha recoil on a low budget.
At what point does one need to take precautions not to blind pilots above?
In the general driection of the beams there is a small airport within range of the lights and it shuts about 9pm after that there isnt many planes. If I have them on and see a plane I kill the light. As they get brighter and longer range I have to be more careful. I would like to hire a plane set them up fly over and light the sky up to see what it is like.
What do you suppose the little arrow is meant to indicate? Does it seem to have a different curvature at right angles to the arrow, e.g. vertical plane versus horizontal plane ? See the bold note below.
From the history:
“Parsons introduced many improvements in construction. The silvered side of the glass was protected by a coat of copper deposited electrically, and later on further protection was given by an additional backing of sheet lead reinforced by wire netting. This rendered the reflector immune from damage by exposure to oil fumes, salt water and other destructive influences met with in service. It also greatly reduced the risks of breakage. Indeed, a mirror protected in this way may remain serviceable after being pierced by a rifle bullet or a shell splinter.”
“Parsons, however, did not confine his efforts to the perfection of parabolic reflectors for throwing straight parallel shafts of light. For certain purposes, as for example when a large area such as a harbour or the landing ground of an aerodrome has to be illuminated, what is required is a flat divergent beam. To produce such beams, Parsons invented and devised methods for the manufacture of a most ingenious form of reflector, curved to a parabolic form in the vertical plane and to an elliptical form in the horizontal plane, both curves having a common focus. The parabolic curvature resulted in the light issuing in a beam of uniform depth, while the effect of the transverse elliptical curvature was to cause the rays first to converge into a vertical line at the secondary focus of the ellipse, and then to diverge at a predetermined angle. Searchlights equipped with such reflectors therefore not only projected a fan-shaped beam of the required type, but the whole of the light was able to pass through a narrow vertical slot situated at the secondary focus. Consequently the searchlight could be operated behind a loop-hole where its chances of being damaged by rifle fire would be very slight.”
That’s some beautiful countryside and CRAZY beamshots. Wow 
Kennybobby,
It doesnt look like it, seems to be equal focus. If I hold the OL comp light at the focal point it will focus back and burn your hand. If I turn it a little it will throw the beam out. I think the light they are talking about it more square. When I get a stand/cradle built for it I will have more of and idea. I also want to set it up so I can swap the light engine. Now I need a new AC/DC tig welder to weld aluminium it is too big to take to work.
When you start dealing with lasers instead of flashlights.
Did some work on the zoo-me-150mm this morning. The drawing is a work in progress, usually I build things without drawing them except for electrical circuits. the piston/heatsink is 42mm diameter. The lower bush will be 42mm long. A copper or aluminium sleave? Will cover the magnetic limit switches. To save length the motor will be noncaptive mounted in the piston. I am yet to work out how the cables will lay when the piston moves.
Nice looking job on the machining—copper can be difficult to get a good finish; its so soft, gummy and grabby causing lots of pull-outs.
Are you looking to use a traveling-screw type actuator with the screw passing thru the motor.
I use a lot of high speed steel so I can make the cutter I want. I find the last few cuts need to just skim the surface off. 8 use high speed chuck. Wd40 and slow feed. Takes times and hone your cutter probably most important. There are 5 pieces of copper bar there silver soldered together.
Yes that type of motor, I was going to have a fixed motor but this way will be better.
Not sure how to do the cables yet. I could bore a hole next to the barrel with a hole for the cables to pass through. Put a spring loaded plunger in there to push any slack down the bored hole. The other thing is if there are no snags the piston will just bundle them up
i made some notes on one of your previous drawings just for talking purposes.
Do you see this as 3 Lens as marked, is that a correct assumption?
Is the distance from L2 to L3 fixed?
For focusing you are wanting to move L1 (fixed to LED) with respect to L2?
Would it matter if the L1 to L3 was fixed and L2 was moved for focus?
i was looking at a concept in which the heatsink was shortened into a collar piece that is press or shrink fit onto the copper tube at the L1/LED end, and then move L2 for the focusing.
It is hard for me to explain probably because I dont really know what Im talking about. I only know what i see and I dont know how it works it just does.
Yes it could be looked at as a 3 element lens. L1 is fixed and wont change although I suspect aperture has something to do with the beam characteristics. If L2 and L3 are fixed L1 can be moved to focus the lens. In a follow spot the light is in an elliptical reflector. This reflector focuses to a second spot which is what the lens focuses on. In these spotlights they move L2 to adjust the beam size. Depending on where the elements are changes the beam shape.
To zoom in L2 moves toward the led, L3 moves away from L2.
Zoom out L2 moves away from the led. L3 move toward L2.
When I write it down, that is why they only move L2. But after thinking about this, L3 has to move to zoom in and out.
My idea when building the light is to cut down the amount of light hitting the barrel of the lens reducing stray reflections. So L1 is designed to only let light out that will hit L2, when fully zoomed in the light from L1 only illuminates the centre of L2, zoomed out light from L1 illuminates all of L2. The reason for this is that at all postions of travel L3 is fully illuminated. That is the reason why I build 2 soon to be 3 element lens lights. They are hard to get right, i will eventually.
Edited to clear it up
Took the mirror outside to see how it fitted in a temporary stand I made for it. As i walked into the sun the mirror burnt my ear. It is dangerous in the sun.
Didnt do what I planned over the weekend but I did work on lights. Waiting for 310mm and 250mm glass lens.
11inch search light.
9 1/4 inch on reflector for it yet.
