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If you have old camera lenses, a macro bellows and a high power LED flashlight, you can use those to build a battery powered projector.

As high power LED lamps are much more efficient than classic slide projectors, and camera lenses are often brighter than their often cheap projector counterpieces this can be a very powerful combination.

I've done projections over 200m distance, using a Cree XM-L T6 light and a 400mm f/5.6 lens.

Step 1: Select the Right Flashlight

The outcome will depend largely on the flashlight you chose.

The ideal flashlight would evenly light a tight spot of 45mm diameter (the image area of a 35mm slide) at very close distance and as bright as possible.

Indicators for good flashlights are:

  • ultrabright (around 1000 Lumen, comparable to a car headlight)
  • with Cree XM-L or XM-L2 LED's (those are most efficient)
  • long range over 100m, a deep parabolic reflector with a diameter of ~45mm
  • enough juice: at least 4xAA or 2x18650

An example for an affordable matching flashlight is the chinese SomeFire X8 model (for example UltraFire X8).

Step 2: Pick the Right Lens

Projecting works best with very bright or very long lenses (but not with zooms!).
Here's a list of lenses that have proven useable, together with their estimated 2nd/3rd hand market price:

  • 50mm f/2.X ($5..$15)
  • 50mm f/1.X ($15..50)
  • 135mm f/2.8 ($15..25)
  • 200mm f/3.3 or f/4 ($20..40)
  • 400mm f/5.6 ($30...)
  • 500mm f/8 ($30...)

If you don't know what to chose, i recommend to select one of the following lenses

  1. 135mm f/2.8 -will project a spot at a distance (5 Meters up to 50m)
  2. 50mm, which projects a larger image at shorter distances (2 Meters up to 30m)
    f/1.4 is ideal, but f/1.7 and f/2.8 will work too (though darker)

Step 3: Prepare the Bellows

You will be cutting slits into the bellows in order to position the 35mm film just where it would be in a camera or slide projector.

In order to do that, just extend the bellows halfway and measure a distance of 44mm from the lens flange. This should be within +/-3mm to the exact flange focal distance of your lens (you can adjust it with the bellows)

Now make two incisions to the left and right side of the bellows, and insert the 35 mm film.
Just be careful to make them horizontally centered, symetrical, and not too wide.

Insert the 35mm film with the image bottom-up.

Step 4: Attach the Flashlight

You will have to find some way to attach your flashlight.

I used M42 extension tubes and gaffer tape, you might find another solution. Whatever works :)

Step 5: Start Projecting

Congratulations! You should have a working projector.

If you'd like to have this in a more solid form please have a look at the GuerillaBeam 3d printed projector. :)

<p>Hi</p><p>Thank you for sharing you idea. It's excellent. I have a question<br>regarding large display on screen within short distance. So which equipment<br>should I buy? Thanks</p>
Generally and personally, I'd recommend buying or 3d-printing a GuerillaBeam projector (which I happen to produce ;-) ).<br> To answer your question specifically:<br> For a large screen and short distance you need a lens with&nbsp;<em>short</em> focal length (aka. wide angle lens).<br> You can find out which lens best suits your needs by calculating the throw ratio (distance divided by image width) and looking it up in the table here:&nbsp;<a href="https://gbeam.de/knowhow/35mm-lenses/#lens-comparison" rel="nofollow">https://gbeam.de/knowhow/35mm-lenses/#lens-comparison<br> <br> D</a>id this answer your question?
<p>What flashlight would you recommend on Amazon?</p>
<p>From where did you get the film?? :O</p>
<p>It's just transparency sheet, and an inkjet printer. </p>
<p>Where did you get the images? </p><p>Very nice project, I have to try it! :)</p>
<p>The images I get from the internet, or I design them myself, using for instance Inkscape.</p><p>Then I print them on transparency sheets (that is normally used for overhead projectors).</p>
<p>Nice idea, also the led illumination is not so hot as the halogen bulbs in slide show projectors. A clever addition would be an adapter for common slide frames between lamp and bellows. Maybe a thing to 3d print ;-) </p>
<p>As you mentioned 3d printing:<br>I did it. Please have a look at http://guerillabeam.net.</p><p>You can also find the 3d models free at https://clara.io/user/universalist</p>
<p>put a stripted lcd screan without the backlight just the transparent crystal insted of the slilds you could send movies i tryed that with the old a4 projector and a broken lcd screan works perfect</p>
I tried this, but LCDs give much darker images which i find unsatisfying. Also it makes the building way more complicated.<br><br>Maybe my follow-up project &quot;GuerillaBeam&quot; will mate with some of the LCD projectors that are already to be found here. It's not on Instructables yet, but it could easily be modified to acommodate an LCD module. :)
<p>you could also compensate the bright spot in the midle by diming the center of a slide or puting a dimed filter bihind a slide could give you a veter quality &quot;beter then my englisch lol&quot;</p>
OMG! <br><br>This is in the same family as my submission (fear not, it isn't the same thing) <br><br>I've done lots of tinkering with and bookmarking of resources and parts that might be useful <br><br>If there are any snags you run into, I'd be happy to share any of the resources I have that might save you a few hours and/ or dollars.<br><br>On a side note, I've also played a lot with things along the line of quadrat's suggestion
<p>Very clever!</p>

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