Mystery optical device

Having a weed-out I came across something I bought ages ago at a garage sale for 2 quid with no idea what it was - it just looked interesting. Still no idea what it's for, but maybe someone here will know....

Here's what you see when looking into the four apertures:

I'm struggling to imagine what this would have used for - any ideas?

Robin

Probably from a DLP [digital light projector]

MichaelG.

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Edit: https://electronics.howstuffworks.com/lcd-projectors1.htm

Edited By Michael Gilligan on 01/02/2019 21:13:57

Colour enlarger ?

Roy

Thanks Michael, but can you explain (or point me to an explanation) of the need for its curious optical properties?

Robin.

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I've just edited my post ^^^

It's a trichroic prism used to split incoming light across three mono image sensors giving much greater sensitivity than a bayer matrix.

Neil

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Depends which direction the light is travelling

MichaelG.

Indeed, but you know my interests are biased towards imaging

I've found them on Wikipedia, but called 'dichroic'.

en.wikipedia.org/wiki/Dichroic_prism

and this:

en.wikipedia.org/wiki/Three-CCD_camera

Would be good for astrophotography, although getting three specialist cooled mono cameras at ~ £1000 each might be a bit of a barrier.

Neil

Edited By Neil Wyatt on 02/02/2019 20:32:36

You might want to play with one of these, Neil:

**LINK**

https://www.surplusshed.com/pages/item/L14828.html

MichaelG.

Neil is correct, but the simple expanation is that it is from a older colour TV camera where they had individual detectors one each for Red Green and Blue. The device separates the colours and feeds them to the correct sensor, probably a Vidicon vacuum tube. They are still used in higher quality CCD cameras -3CCD types.

Robert G8RPI.

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It's a good job I only claimed 'probably' then

MichaelG.

Most DLPs use a simple rotating filter wheel but some of the early high end ones use a combiner similar to the splitter shown but it's easier to combine colour than split them so simple methods are used. The spliter uses "dichroics" that reflect one set of wavelengths and transmit another.

Similar devices are used in fluorescence microscopes. I designed equipment using this stuff for several years but have now gone back to aviation .

Neil may be interested to know that I used to use Starlight Xpress cooled CCD cameras in instruments. They were sooo much cheaper than "proper" scientific ones that used the same, normally Sony HAD, CCDS. This come back to topic because these CCD are monochrome and intended to be used 3 at a time for high end video cameras that use dichoric splitters like the one pictured (but smaller). Being for a small market CCD availability was sporadic.

Robert G8RPI.

Thanks! A trichroic prism it is then. Because it's mounted on a wooden base I guess it came from some sort of bench demonstration rather than having been part of a projector or some sort optical instrument or camera.

MichaelG - thanks for the link to howstuffworks page, but I have to confess that the explanation given there confused me. I understood about splitting white light into RGB components, but it goes on to say:

"All three of the LCD screens in the projector display the same image or moving images, only in gray scale."

Unfortunately the author of the article doesn't seem to say that the original image must have been split into RGB components, and the intensity of the of the individual components must be represented by different degrees of grayness. I may be guilty of having read 'same' as 'identical'. Not the same are they?

If anyone can use this thing let me know - no use to me, but it will sicken me to bung what may be a precision made thing into the bin.

Robin.

Edited By Robin Graham on 02/02/2019 23:34:09

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Robin,

I would say that your 'guilt' clearly demonstrates that you have understood the process

... I will send you a P.M. regards re-homing the thing.

MichaelG.

I found something like that in a box of old vidicons, pcbs etc. Inside the bigger triangular box are a couple of front surface mirrors and a dichroic block like one shown. I got it for the input output lends units (nice eyepieces). The block shown is 50mm on a side and carries two pretty coloured bits of glass. Basically it takes in an image, splits up the colours and shoves out 3 beams to the vidicons.

If anyone wants the dichroic mirror block shown you can have it, just a PM.

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P.M. sent

MichaelG.

There is only one (very obscure) colour photographic process - Lippmann - all others, film or digital record images in mono, which may later be dyed or filtered to give colour.

If anyone is interested the book 'Colour Photography' by the late Brian Coe is a fascinating history of film colour photography.

No, sorry, its actually intended for parties. You produce it and say 'What is this for?' and while everyone is arguing you get a clear run at the punch bowl ...

Tim

Many thanks to Robin, and to Roger, for their donations to my "must find a use for that" collection ... hours of optical fun ahead !!

Robin's device is nicely mounted as a demonstration-piece, and [although he numbered & lettered it differently] is apparently identical to the model explained on the Wikipedia page: **LINK**

https://en.m.wikipedia.org/wiki/Dichroic_prism

MichaelG