[Leica] Time-line: focal length in centimeters versus millimeters on projection lenses, Epidiaskop IIIs

["Willem-Jan Markerink" <w.j.markerink@a1.nl>]

Dear group,

Last week I became the proud owner of what must be one of the most 
unique pieces of Leitz projection equipment, the Large Lecture Hall 
Epidiascope IIIs[*]....a monstrous steel contraption, 211cm tall, 
64cm wide, 94cm long, 300-500kg. Needed a full-size horsetrailer with 
loading-ramp to haul it home, 5 men for pushing it in the trailer, 3 
men for controlled unloading....8-))

Here a preliminary image, lenses removed:

http://www.a1.nl/phomepag/markerink/epimonst.jpg

However, even though I bought it from the university where it had 
been in active duty many many moons ago, it had been so long out of 
duty, pushed aside in a projection room, only recently being forced 
to move due to demolishing of the lecture hall itself, that no body 
knew its year of build or purchase....it even preceeded the career of 
the current janitor 
("It's old Jim, but not as we know it...."....8-))

My only time-line reference is the fact that I already had an 
episcopic lens from another IIIs, with different focal length 
annotation; 1:3.5/700mm instead of f=100cm/1:3.5 (both 'EPIS', and 
yes, that's 20cm & 30cm lens diameter....the big one is too heavy to 
lift to chest-height(!)).
Can anyone tell me whether this helps putting a date stamp on it, at 
least accurate to a margin of a decade?

Serial number of the projector itself is A87052, but I doubt that 
helps anything, unless a few known samples around this number exist.

Oh, diascopic projection (up to 4x5", wooden slide-adapters of 
14x14cm) is 110v/1500W (E40 lamp), episcopic projection is 4x 1500W 
(with lens/condensor between lamp and paper, each lamp one lens, 
never seen that in smaller episcopes; probably a must in large 
lecture halls because of the highly inefficient nature of the 
episcopic projection (reflective)). Episcope lenses are 50cm/1:5.7 
and 60cm/1:4.5, in a dual/revolver set-up (for slightly different 
formats of slides)....same lenses are used on smaller Diaskop and 
Epidiaskop.

[*] have yet to find the official German name, did speak to Leitz 
folks on the PhotoKina, who agreed with my 'Grossraum Epidiaskop 
IIIs' translation....further cooperative research is pending, as 
hardly anyone working at Leitz today knows much about any 
(Epi)Diaskop....either they are able to trace down one or more 
senior/retired employees, or I might get an invitation to do research 
in the Leitz archives itself....ah, the honor!....:))

See also....

http://www.a1.nl/phomepag/markerink/epimonst.htm

....for the only picture from a IIIs I have found in Leitz literature 
thusfar (this one has a 130cm episcope lens, 70cm diascope lens, but 
with 'internal' focus, unlike the 'open' screw-collar of both my 
700mm and 100cm episcope lens (and both diascope lenses as 
well....only on an older & smaller Epidiaskop I have such 
sliding/internal focussing lenses)  

Only one time before have I seen such a IIIs projector being traded, 
in the UK (within some kind of association of historical photography, 
tried to track down more info back then, but failed due to their 
shielded membership structure (internal auction)).

More about the last range of 'smaller' Diaskop and Epidiaskop (until 
late 60's) on:

http://www.a1.nl/phomepag/markerink/diaskop.htm
http://www.a1.nl/phomepag/markerink/epidiask.htm

Bottom line:
If *anyone* knows more about *any* of these projectors, in particular 
this huge IIIs, please step forward, in the name of optical/academic 
history....;))

- --                 
Bye,

Willem-Jan Markerink

      The desire to understand 
is sometimes far less intelligent than
     the inability to understand

<w.j.markerink@a1.nl>
[note: 'a-one' & 'en-el'!]


- --
To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html