GuerillaBeam slide holder

GuerillaBeam is a modular flashlight image projector.

A GuerillaBeam projector consists of this slide holder, an attached photo lens, and light. The light is typically an adapted Cree XM-L flashlight, but other light sources (strobe lights, e.g) might fit and work as well.

What to expect

• image brightness comparable to conventional projectors with 100 Watt
• to fit 2 mm photo slides (usually glassless, like the current Agfa CS2 format)
• projection range between 1 and 150 m
• good enough image quality, (much) higher resolution than digital projectors. 

Compatible devices 

• any SLR camera lens (Canon, Nikon, Pentax e.g.)
• photo projector lenses with (standard) tube diameters of 42, 52 and 62mm
• high power LED flashlights and other

How to make:

Firstly, determine the thickness of your 35mm slide mounts. There's one version for slides with up to 2.00mm thickness (i.e. Agfa CS), and another one for thick slides  up to 2.5mm.  (Other sizes available on request).

1. Print the slide holder.

• Wall thickness of 0.8mm and layer height <0.2mm is recommended. Assuming there are no major defects in your print, this will suffice to support lenses up to 2kg.
• Recommended infill percentage is 23%. With greater wall strengths, it can also be zero.
• For FDM printers, and for the slides to fit, you will have to print with support material. Its only a minimal amount at the slide slot, but it's crucial. Using Cura, automatic support generation for overhangs >51% usually works perfectly. With other slicers you might have to manually place support material.

2. Install a condensor lens:

To work as intended  the projection device requires condensor lenses or it will only work with reduced brightness, not covering the whole image area of your slide (typically only a 20mm circle). The simplest way of obtaining a suitable lens is to get a credit card magnifier lens, cut it to appropriate size (38x48mm) and carefully place it into to the corresponding slots (located right next to the slide slot).  A single lenses with around 100 mm focal length (10 dpt power) ususally works, but you might want to try and experiment with other lens values. 

Lights 

A good basic light can be any focused Cree XM-L flashlight. Those are sold from $10 upwards and typically use 18650 batteries. Especially suited is the TrustFire X8 (or the slightly inferior UltraFire X8). Lights with multiple LEDs (like ThruNite TN30 or Sky Ray King) can give even brighter images, but yield lower efficiency and can cause overheat problems.

Suitable photo lenses

Any lens with an  f-number of 2.8 or less will work fine, provided there's an adapter for it. Slower lenses (f/3.5, f/4, etc.)  will work too, but only with significantly reduced brightness and image quality.

Recommended focal lengths are between 50mm (most powerful, lightweight and affordable) up to 200mm (long range, but costly at f/2.8).

Slides

You can use common classic photo slides of 50 by 50 mm (2 inch) size with thicknesses up to 2 mm. The best slides come from professional photo labs, but you can absolutely make slides at home by printing on overhead transparencies. Despite inferior slide quality, this method is usually sufficient and (more importantly) reasonable quick.