This is a beautifully-made, brand new item and we thoroughly recommend it if you are planning to build a right-angle telescope or are going to build an erecting star diagonal.
The prism diverts the light path through a right-angle AND it gives complete inversion of the image. This means that it turns an astronomical image upright and the right way round.
In other words this prism can be used to turn an astronomical refracting telescope into a terrestrial spotting telescope.
These prisms are military, unused and of the highest possible quality.
Face size: 25 mm x 27 mm
Price: £55.00
This is a much larger and lower quality item than the PR6. It is of military origin and has been stripped out of wartime high-angle gun sights.
All these prisms have some chips and scratches but all are of useable quality. The prism diverts the light path through a right-angle AND it gives complete inversion of the image.
Face size: 63 mm x 39 mm
Price: £15.00
This fascinating beam-splitting prism has been stripped out of wartime military optical systems
All the items that we have in stock have some edge or corner chips and some slight marks in the anti-reflection coating but they are all of useable quality.
The light enters one face and is divided UNEQUALLY between the two other faces. A face at right-angles receives a bright image but the straight-through face seems to incorporate a neutral density filter, making this path ideal for lunar observations, where glare can be a nuisance.
SAFETY: These prisms are totally unsuitable for solar observation. The heat transmitted through the prism would cause irreversible damage to the eyes.
Face size: 33 mm x 22 mm
Price: £15.00
This fascinating beam-splitting prism has been stripped out of wartime military optical systems
The exit face of this glass block is a circular convex lens, 31mm in diameter, with a split view; one half views the input from a flat face 37mm X 17mm, set at right angles to it and has a semi-circle and two lines engraved on it. In addition this half of the circular face views the light input to the square face (36mm square) on the opposite side of the cube, using a beam-splitter principle.
The other half of this semi-circular face views an equally concave circular face set at right angles to it. This face is also 31mm in diameter and has a cross-hair superimposed upon it.
We do not know for what this military prism was used, nor can we imagine for what an astronomer could use it, but it is in good condition, is fully bloomed and must have cost a lot of money.
Price: £15.00
The purpose of a dove prism is to cause the light path to be rotated at twice the rate of rotation of the prism. If you look through this prism and rotate it through 90° the view seems to rotate through 180°.
The prism is shown on the left in this photograph. Its faces are 22mm square and are sloped, so that the prism deviates the path of the light through about 70°. It is in a heavy, cork-lined brass cell with adjusting screws. The prism can be easily removed from its cell.
| Total weight including brass cell: | 5 oz |
| Weight of prism alone: | 1 oz. (25 grammes) |
Price: £12.00
This is the same as the previous item but larger; it is shown on the right in the photograph. The faces are 31mm square.
| Total weight including brass cell: | 11 oz |
| Weight of prism alone: | 3 oz. (75 grammes) |
Price: £15.00
This is a rectangle of glass, 145mm x 60mm which is 3mm thick. It is a neutral density filter so it seems to be a dark, smoky grey.
An eclipse of the Sun was observed through a wad of five of these, by looking at the Sun reflected in a bowl of water. The five layers of filter gave the image a deep red colouration.
Price: £6.00
This is a circle of glass, 60mm in diameter and 5mm thick. It is neutral density and is a dark grey.
Price: £6.00
This is a disc of orange glass 33mm diameter and 1 ½ mm thick.
Price: £6.00
SAFETY: NEVER observe the Sun directly through these, or any other coloured filters The coloured filter may remove the bright VISIBLE light, but not the dangerous radiation. Also, of course, the filter might fragment if it were used in a telescope.
Just do not use them for solar observations – there are other methods.
This is a HUGE and beautifully made item. It is a roughly circular hollow brass plate, 7” in diameter and painted black. It was the rear end of a large, American wartime telescope.
Inside this 1 ½” thick casting is a large brass disc, which carries the coloured filters. By turning one of a pair of control knobs, this brass filter wheel can be made to rotate, to put different filter combinations in front of a large eyepiece built into the housing. If this assembly were part of a telescope the view could be made red, yellow, clear and polarizing. By turning the other (‘Density’) knob a second polarizing filter rotates in front of the first, to vary the brightness of that image. Please note that the polarizing filters are in poor condition, but could easily be replaced.
The large eyepiece is a Plossl with a fine-focusing ring. The total weight 5 lb.
Price: £50.00
These are brand new black anodised rings with different threads on each end.
The sizes available are: C49/52, C49/55, C49/58, C49/62, C52/52, C52/55, C52/58, C52/62, C55/55, C55/58, C55/62, C58/58, C58/62 and C62/62.
Price: £5.00 each
This is supplied in its original fitted steel box. The geared head of the theodolite has a worm-driven elevation platform that carries the telescope. This platform can be tilted about 20o above and below the horizontal. The telescope gives an erect image at a magnification of x1. A cross-hair is superimposed on the field of view.
The geared head is 3” in diameter and made of heavy brass. It provides a 64:1 reduction ratio when a graduated thimble is rotated by hand. There is an engraved angle scale, in mils, on the geared head. There is also an angle scale engraved on the thimble, so angles can be measured to less than 1 mil. The worm drive to the geared head is fitted with a disengagement mechanism, so the geared head can be slewed rapidly by hand.
The entire device is carried on a massive ball and socket head attached to an equally massive steel angle bracket.
Weight: 15lb
Price: £60.00 Only 1 left
This is the mechanism on MT. 1 (above) that tilts the tiny telescope.
This mechanism could be used to tilt a tiny optical component such as a mirror or a prism within an optical system or, of course, you could use it to tilt a very small sighting telescope to carry-out some measurement.
Price: £10.00
We make worm-wheel sets ourselves, to order. The worm wheels can be made of either aluminium alloy or brass. The teeth are cut at 20 teeth per inch, so a 6” diameter wheel would have about 380 teeth. Each wheel is ½” thick and the central boss is 1½” thick. We bore the boss to accept 1″ shafts, but it can be bored to accept other shaft sizes at an extra charge.
The worm that causes the worm-wheel to rotate is mounted in shielded ball races, held in a sturdy aluminium alloy or brass bracket. The worm is mounted on ¼” (6.35 mm) silver steel rod.
The smallest diameter worm-wheel that we will make is 6 inches while the largest diameter is 10 inches.
All our worm-wheels are made to order so the price will depend upon the requirements of the customer.
This has a short, helically-grooved draw-tube. A spring-loaded ball-bearing presses into the groove so that the draw-tube moves in or out when it is rotated. There are clamp screws for both the draw-tube and the eyepiece. It is made of brass and can be finished in satin black or left as polished brass.
We can make this in a 2” version.
Price: from £150.00
This is a black plastic instrument knob with deep, semi-circular indentations around the edge so that the operator can achieve a firm grip. On the rear face there is a brass insert to accept ¼” diameter shafts.
Price: £5.00
This x-y stage has a base plate on which the two rectangular tables slide. There is a I” diameter hole through the base and both the sliding tables. The tables (6″ x 4″) permit movement in the X and Y axes. There are brackets at the side of each table to hold a micrometer thimble so the table’s movement can be accurately measured or adjusted. Each table moves by about I” against a powerful spring. There is no free movement in the slideways.
You can use these for their original purpose, which was to measure items under a microscope, or you can adapt them to hold components on the lathe, while carrying-out light milling or drilling operations. We have used one for years, to hold worm-wheels while the lathe cuts the teeth in the rim of the wheel. Black anodised and very heavy, these magnificent precision items are brand new.
Price: £50.00
This is a very dark brown material. It can be drilled, tapped, turned and glued. It is useful for making plugs for the rear end of refractors or just for general construction work. Each block is nominally 6 ¼” X 4” X 1 ½.
The material is made of layers of paper bonded within synthetic resin. When you are deigning items made from SRBP you should be aware that it will split along the layers if you apply tension across the ‘grain’, just as timber will split.
Safety: Wear respiratory protection and eye protection when you are handling SRBP. This material is a good heat insulator so drills get very hot very quickly when you are drilling it. This heat can cause the drill to jam in the material and then either shatter or pick-up the workpiece, with danger of injury to the operator. In addition the dust from sanding and the fumes from machining are irritating and potentially harmful to the lungs.
Price: £7.00
This is a hard brown tube that machines and threads beautifully. It is tough, light and may be glued. This material is ideal for bushing, making small lens cells etc. It cuts easily with a hacksaw.
Take note of the safety precautions needed when handling SRBP.
The tube has an outside diameter of 2” and a bore of 1.45”.
Price: £6.00 per foot length
This is an excellent heavy brass tube that cuts and machines well. The outside is coated with textured black paint.
The dimensions are 48 mm O.D., 45 mm I.D. with a length of 79 mm.
Price: £7.00
These handsome screws have a slotted, knurled head and a 1” long thread. They can be used as clamp screws, such as in finder rings, wherever it is important not to bruise the material that is being clamped.
Price: £0.60 each
These screws have a large, knurled head and are very attractive. The thread is ¾” long.
Price: £0.60 each
Each ring is mounted on a pillar that is provided with a ‘foot’ by which the ring is bolted to the telescope. The curvature of this ‘foot’ will match the curvature of the customer’s telescope tube.
Each of the six adjustment screws is provided with a soft-lined pressure pad (not shown) to cradle the finder telescope, so that it is not damaged when the adjustment screws are tightened.
We recommend these luxurious brass rings whenever appearance and quality are of the essence. They are supplied with four brass 2BA cheese-head screws to mount the rings to the telescope.
Price: From £200.00 per pair