Sunday, 23 September 2012

The Ross epidiascope

It's been a long time since I posted here - sorry folks. The day job got in the way, and then somehow I got out of the habit. I'm going to try and post about once a week for the next few weeks. (Maybe once a fortnight might be more realistic.) Let's see. Anyway the plan is to try something regular, if not frequent.

A Ross Epidiascope

I like old gear, and I like fiddling with old stuff to try and get it to work. And I like my photographs big. So when the possibility to buy a beast like this came up I went for it, even though I hardly need another project, and have only just enough space to keep it.

Ross Epidiascope

OK. What is it?

An Epidiascope is like an old-style slide projector or magic lantern and overhead projector built into one. It would have been used mainly for displaying images during lectures, talks and so on. So education was the main market, though no doubt they were used in cinemas, military etc. The gadget has a dual function, and I guess this is made economical because of the powerful light source.

Dia function

The more familiar function is that of a slide projector. That's the "dia" part of the name, from the Greek for "through", and in most languages but not English the word for "slide" is based on "dia". ("Das Dia", in German.) This slide projector is no ordinary 35mm projector like I remember being terrorised with by neighbours just back from their holiday. ("You must come round and see our slides.") Instead of projecting a 24x36mm image (or even a 56x56mm image if you are lucky enough to work with MF slides on a Hasselblad) the slides are three and a quarter inches square. So images of 80x80mm or so can be displayed, with correspondingly better resolution and punch. And instead of a perhaps 250W bulb, the epidiascope has a 1000W bulb for four times the brightness, or four times the area. That at least is the theory. I want to try it out.

The lens used is a 10.5 inch projector lens of about f/5. That was obviously intended for a fairly long throw, as well as coverage of the larger slide. I will have to see how it performs for me, but a wider lens might work better in my limited space. This is for experimentation as well. In any case the lens seems a good one and may also be useful as a taking lens for 4x5. Watch this space.

Epi function

The other function is the "epi" one, and this refers to projecting the surface of an opaque object or drawing. So in this respect the epidiascope behaves more like a modern day visualiser. The object to be projected is placed on a movable tray under the projector and can be brought flat against a glass underneath it. The light from the huge bulb is split into two paths and reflected off two mirrors in the side of the gadget. It illuminates the object, and the light reflected off it is reflected by a mirror and projected by a huge 17inch lens. The combination of the mirror an the lens restores the object to normal way round. (As opposed to upside down or mirror image.)

The area projected is about six inches (150mm) square. So quite large images should be projected. Once again, I need to try it to see how well it works in practice. Watch this space!


I have no idea how old this object is. Ross marketed models very like this as early as 1932 and up to the 1960s. Mine appears to be a later model as it has a fan added on the front. Mine is similar but not quite the same as this one and a contemporary advert for a very similar one is available on-line here: Mine is Type B.E model 2, which suggests it's not the oldest. More information would be gratefully received!

My plans are firstly to get it going and see how good it actually is. That means cleaning it carefully and re-wiring it inside. If the bulb inside is no good or blows, and it looks like I will continue to tinker with it I will probably replace the original bulb with a modern and more easily replaceable halogen one. I would also like to try making old-style three and a quarter inch slides. If all else fails these are very interesting lenses to try out. We will see...

Ross Epidiascope: open

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