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Magic lantern project

Liesegang's 'Janax' Magic lantern

While strolling on the weekly antique market in the city of Delft, this nice looking magic lantern projector showed up.
I have always wanted a magic lantern, so this was a great opportunity. The projector is a "Liesegang Janax" epidiascope, from around the 1918's. This means that it can do both projection of slides (like a slide projector) and other objects (like a overhead projector). Next to buying the projector, I also bought one box of glass slides from some kind of expedition in Norway.

Magic lantern Type Janax

The lantern was already of the "electric" type: a 500 Watt lamp would normally provide the light. The ultimate goal is to replace the lamp with a LED lamp and turn it into a digital projector.
Keep reading to find out more about this project!

Optics: The lenses

The lantern consists of 4 different lenses. Two for light accumulation, and two as a projection lens: Magic lantern (Janax) lenses

And how they are placed inside the lantern:

Magic lantern (Janax) lenses

Unfortunately, there are two problems with the lenses. One lens has a damaged corner, and the other is full of airbubbles. Apperantly airbubbles are not necessarily a bad thing (atleast, not in the early 19's wink), but they definetly do show up on the image. And so the quest for two new lenses started. These lenses are quite old which make it difficult to find a replacement.

One lens bears the name "Liesegang No. 10" (or No. 16) which apperantly is a German system for classifying lenses. I have not been able to find any useful information about this system however (if you do so, let me know!)
So, it has to be done through a more difficult approach. The first task is determining the focal length. I have done this semi-accurately using two laserpointers taken from broken memory sticks.

[picture]. Two parallel laserpointers (placed way beyond the expected focal length) should merge together at a certain distance behind the lens. This distance should be the focal length, if I am correct.

This lead to the following information.

Lens Diameter Focal length Thickness Type
Lens 1 42mm 270mm 1mm
Lens 2 50mm 55mm 2mm
Lens 3 115mm 85mm 41mm Aspheric
Lens 4 114mm 260mm 19mm PCX

Currently I am trying to find out if it is possible to find lenses which match most of these characteristics.

Display: The TFT display

In order to turn the projector to a digital projector, it needs a way to present the image to the display. Through an instructable I found some information about using TFT screens for exactly this purpose.
At eBay there are so many TFT displays which have composite connectors, which can directly connect to the RaspberryPi. This is the approach I decided to go for, as an experiment. After a couple of days the TFT came in, and after opening it, removin the backlight, and all kinds of thin layers on the TFT displays itself, it was ready to put inside the projector. At the same place as a normal slide.
Using a simple flashlight a little bit of display was visible. RaspberryPi connected to TFT

Putting this together in the front part of the magic lantern, resulted in the following setup: MagicPie

More light

Realizing the small flashlight was definetly not going to emit enough light, another item was bought on eBay. This time a 50 watt LED light with adapter. Upon arrival I connected it to an old CPU cooler from an Athlon XP 2600 machine and powered it (just for the sake of testing) by a 9.6v battery.

LED with CPU cooler

Later the power supply will be merged with the other supplies. For now this is quite practical. I also plan on making it temperature controlled.

Current status

With a glass slide (left) and TFT panel (right) Currently I am trying to find two important parts for my projector, which is a rather difficult task:

  • »A better TFT screen with high resolution with a maximum size of 4.3". a 1024x768 resolution would be nice.
  • » Replacement for the collimating lenses.

Finding the right TFT display is a difficult task, as searching is a difficult task: searching on quotes (like 4.3") does not work very well in search engines, and a 4.3 or 3.5, even between double quotes will in many search engines also match for a "10.5".

One proper site I found is Panelook which provides an okay search engine. The Truly TFT7201280-4-E panel looks like a great display (4.3", 1280x720!), but there is not much information to be found about it :(.

For the optics I am considering Edmund optics or their more experimental quality lenses from Anchor optics.

Written by Almar Joling.