Turn a Regular Video Projector in Short-throw Model for ~40$




Introduction: Turn a Regular Video Projector in Short-throw Model for ~40$

About: ...my preferate breakfast is herring in cream sauce; Ja !!

As a video artist, I like to perform video projections directly from the stage. I appreciate this approach because it's easier and faster to install than to hang video projectors on grill-top or less complicated than other installations. Done well, this technique has good results especially with retro-projection, but the efficiency is often limited by the depth of the stage.

To fix that, the easiest solution consists in using short-throw video-projectors, but it may be expensive especially when you're looking for high light-power (e.g. almost 3000$ for 5000 lumens). So I've looked for a cheaper solution to turn my 6000-lumens-video-projectors into power full short-throw projectors.

I've done a lot of research and tests with mirrors; interesting but less practical to use, to adjust and too fragile to transport. And finally, one day when I was taking pictures, I just thought about how the light goes through a wide angle objectif. That's it ! I was looking at the same principle..... but from another perspective. ^^

That's for the story. The solution was easier: just find a way to fix and adjust a kind of wide angle lens in the same way as my video projector's light field.

Step 1: What Do You Need ?

To do so you'll need:

  1. a wide angle lens converter like these below: ~25-30$


    Even if I chose the lens randomly, this brand is a good one. There's a number of different models and quality available on the web....

  2. a short squared aluminium pipe (e.g. like 15x15x~300mm) ~2$
  3. some screws and bolts (M6 metric screws, autostop nuts, rings, handle,...) ~10$
  4. access to a 3D printer (ask your grand-ma, she has one !), free

Step 2: Prepare Your Video Projector to Receive the Lens Support

Because there's too many types of video-projectors, it is impossible to propose a common support that matches all projector. I'm showing you, in my situation, the technique I used to fix the aluminium pipe and I'm sure that your creativity and ability will help you to find a way to have the same (or a better) result.

I used a wooden board as support below the projector. I use it to hang the projector and I took advantage of this support to fix on it a counter-pipe that will receive the aluminium pipe. I think it should be easy to create an equivalent with wood or hardware components. The important thing is to take care : the pipe must be inline and as aligned as possible with the objective of the projector.

Step 3: Print Your 3D Parts

To have a fully adjustable installation, I used three different parts. As you may see, the parts look quite massive. at the beginning, I put too much torque on the screws and the clamping sections broke ; so I increased the size. It's also explained by the fact that, in order to use it, the system must be robust enough to resist the fast manipulations, and to be rigid enough (without any movements) to allow a long installation (in my case, up to 8 hours).

Base support: makes the liaison between the aluminum pipe and the support. It allows the lens to be moved away and adjust the vertical position regarding the projector lens.

Spacer: allows the adjustment of the lens' height on a vertical axis

Lens support: clamps the lens and allows to adjust the lens' inclination

Step 4: Assemble the System

All screws and bolts are metric M6. Feel free to modify in order to have a more compact system.

To allow fast adjustment I chose a kind of plastic handles (but it's not needed). As you may see on the picture, commercial screws may not have the right length to fit the system perfectly (or like me, you don't want to buy new one ^^). So, you can adjust with some washers, saw the screws, adjust the size of supports to fit,...

If you want to use multiple lenses, you can pre-mount the lenses on the support to have a faster switch. Using different plastic colors allows to easily identify the model of the lens support.

Step 5: Calibrate...

Once the system is mounted, use the different adjustments to place the lens in the center of the projector's ray of light. Display an image that uses the whole illuminated surface of your projector (like a test pattern), have a look from the side and adjust the lens to display, through this, all the rectangular images (when there is a bit of dust on the lens, it's easier ^^). Do not try to fit exactly the rectangle to the border of the lens, it's better to have a small gap to use the center of the lens more (see picture).

Step 6: Enjoy !

From an optical (or professional) perspective this system could not replace a real short-throw video projector; but it has saved my "lives" a number of time... :)

Result: (with a 0.43x lens)
The result is acceptable especially when considering the price and the work time (~10 hours). This lens system allows to gain almost 125% of added surface. Without lens (projector at left), it displays a 51x38.5cm image and with the system, it jumps to 76.5x58 cm. It increases the dimensions 1.5x, and the whole displayed image around 2.2x.

Experience feedback after a couple years:
The weakness of this system is the distortion and chromatique aberration generated by the lens (see pictures). The wider the lens angle (or ratio), the greater these problems will be. A good compromise for me is situated around x0.5 (I use the x0.47 lens 90% of the time). In my opinion chromatic aberration is often negligible because it is especially noticeable when pure white is projected.

You can fix the distortion by different means: with the help of a mapping software, by deforming the projected surface, modifying the image or video source,... It also should be interesting to try with different lens quality or suppliers.

Anyway, in my opinion, this solution is reliable, has an unbeatable quality/price ratio and opens up interesting possibilities in terms of video projection (through prisme, light rays transpositions, specific lens effects,...)

Thank you for your interest. Enjoy and I look forward to reading your feedback !!!

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    1 year ago on Step 6

    Why not just use a small convex mirror like they do on ultra short throw projectors? Using extra lenses is almost definitely going to noticeably reduce the image quality which is why all cheap UST projectors use a mirror instead of extra glass.

    High quality lenses are so expensive that it's not worth it for a diy project. Cheap lenses introduce distortion, loss of detail and contrast.

    If working to a tight budget is the goal, I recommend buying a used high quality pro projector off ebay like those made by Barco, Christie, ProjectionDesign, Digital Projection etc. They use removable lenses and most have a short throw option. My Barco F35 has a .8 throw lens. Add a small convex mirror to that and you have a super high quality ultra short throw with 3000 - 20,000 lumens (depending on which projector you start with).


    Reply 1 year ago

    I think it would be more difficult and expensive to get convex mirror that had the exact compound curvature required to "eliminate" distortion. Not to mention that you need a first surface mirror in addition to perfect curvature(s). The author did point out this was not a perfect replacement - it was good enough for his need at the time, and within his skill set. Admittedly, lots of text or thin lines would not be a great use- this is for images and abstracts. A used "name brand" wide angle lens is still 25% of the cost of the used brands of projectors you named on eBay (with questionable bulbs and condition). Very inexpensive "generic" lenses on eBay can be had for even less. "Perfect is the enemy of good enough."


    1 year ago

    This is a very clever solution and one that I've been looking into for more than 2 years (on and off, though...). I tried, like you, with a cheap-ish 0.43x lens from ebay but was quite unhappy with the result. My goal is not having a bigger picture but simply to place the projector slightly closer to the 150" screen. Right now it sits at about 3.5m, which is the distance needed to fill the screen at full zoom, but this leaves only 30-40 cm between the sofa edge and the little Ikea coffee table where the projector is hidden underneath. Ideally I'd want to gain some 50 cm more so that viewers on those seats could be confortable and stretch out. So... yesterday I saw a used Nikon WC-E80 wide 0.8x wide angle adapter that should give me enough room to move the projector forward. My question is, at only 0.8x, woud the image distortion be more acceptable, compared to the cheap unbranded 0.43x? Do you have any experience with that? Cheers!

    Nico Berger
    Nico Berger

    Reply 3 years ago

    Yep; thank's !!