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| PrismsRight-angled prisms divert the light through an angle of 90o, so these prisms can be used to make a star diagonal. They behave just like a mirror, so the final image is laterally reversed.
PR. 2 Right angle prism
£12.00
PR. 3 Pentaprism, faces 30mm square A pentaprism, as you could guess, has five sides. Its purpose is to deviate light through 90o, just like a right-angle prism, but without causing any lateral inversion. You can make a star diagonal out of one of these and the image is still a true astronomical image, i.e. upside down and back-to-front. Since the light path through the prism is quite long there is perceptible light absorption by the glass. The prism is in good condition but there may be one or two small browning marks in the silvering. These marks will not be in focus when the prism is in use. £15.00
PR. 4 Pentaprism, faces 35mm square
£18.00
PR. 5 95 degree PrismThis prism, like the right angle prisms, is intended to reflect light round a corner. It came from a military periscope and is mounted on a short, stainless steel pedestal whose circular base is drilled with five holes. The faces are 33mm square, the hypotenuse is silvered and it is a lovely item. Since it is not exactly right angled I will part with it at low cost. £10.00
PR. 8 Straight-through Amici (roof) Prism This prism is used in a telescope to convert an astronomical image (upside down and back-to-front) to a terrestrial image. If you want to build a small, straight-through terrestrial telescope, this is the prism for you! It is used instead of a pair of erector lenses and is placed between the objective lens and the eyepiece. The entry and exit faces of the prism are 14mm square. The prism weighs 1 oz. (25g) £15.00
PR. 6 Amici prism (right angle roof prism)
 
This is a really lovely item and I thoroughly recommend it if you are planning to build a right-angle telescope or make yourself a star diagonal. This beautiful prism diverts the light through a right angle AND turns the image the right way up and the right way round. In other words this prism can be used to turn an astronomical telescope into a terrestrial spotting ‘scope. This prism is of the highest quality and I recommend it to you
without reservation. I have never seen prisms whose angles are so
superbly ground. The faces are 25mm x 27mm.
PR. 7 Amici prism
£6.00
PR.9 Beam splitter cuboid Bloomed.
The faces are 33mm X 22mm. The light enters one face and is divided
unequally between 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 observation.
All have the odd chip at the corner, and some have slight marks
in the anti-reflection coating. I have used one to build a lunar eclipse telescope with two eyepieces, set at right angles to each other, where the observer can simultaneously watch the eclipse through the straight-through eyepiece and photograph it through the eyepiece at right angles to the observer’s eyepiece. Neat, huh?
SAFETY: Do not try to use these for solar observation, the
power of the Sun's light is too dangerous and could cause permanent
blindness. PR. 10A Multiple prism cube
I just don’t know about this one! Read the following notes carefully because there may be a short written test at the end. 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. Got it? I don’t know what this military prism was used for, nor can I imagine what you could use it for. It is in good condition, fully bloomed and must have cost a lot of money. I’m letting it go at a silly price. Perhaps an executive toy…
PR. 11 Dove prism in holder, 22mm
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 90o the view seems to rotate through 180o. The prism is shown on the left in this photograph. Its faces are 22mm square and are sloped, so that the prism deviates the light through about 70o. It is in a heavy, cork-lined brass cell with adjusting screws. Try to find a use for this one because it is magnificent. Total weight including brass cell: 5 oz. Weight of prism alone: 1 oz. (25gramme) £10.00
PR. 12 Dove prism in holder, 31mmThis 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. (75gramme) £12.00 |
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