Science Buddies: "Ask an Expert"

Hello, AAE!

I am currently doing an output-based science project with a partner. We have decided to pick the field of optics and do a DIY smartphone projector. Most of you may already know about this popular DIY and it really isn't new at all but we are planning to innovate/improve this project and really trying to make it a success. Now, the main con of the project is the inability to produce sharp projections from the phone. In our prototype, we used a biconvex lens with a 300mm focal length. The result was not quite good--the projection was bright enough but we can't get it to be focused or sharp even though we have adjusted the distance between the phone and the lens as well as the projector itself from the wall. Let's say, the quality would be around 144p if I would to compare it to YouTube's quality selector.

Moreover, I have read somewhere that doubling the lens would make the projection quite clear but I still have my doubts. Do we need to use another 300mm lens? Or do we need a bigger/smaller one? What do we need to do to let it produce projections bright and sharp enough to make the viewing experience favorable? I would like to hear suggestions from anyone to help us innovate/improve this DIY smartphone projector. I am really looking forward to your replies.

Thank you,
NaCl-y.

Hi NaCl-y,

Based on your description it sounds like the lens might not be parallel to the smartphone's display. You might try moving the angle of the smartphone relative to the lens to get a sharper projected image.

Another possibility is that the smartphone is too close to the lens to produce a focused projected image. So you might try moving the smartphone away from the lens.

I hope this helps. Please ask again if you have more questions.

A. Norman

Hey A. Norman,

Thank you for your reply! We are sure we have made the lens and smartphone's display parallel. Regarding the distance of the smartphone from the lens, we made room inside the box for adjusting the smartphone to/from the lens as a means of finding the perfect focus.

And that's that, we don't have any luck finding the perfect focus for the projected image. So far, we are stuck with our prototype and the submission will be next week. Is there still hope for our project?

Thanks again,
NaCl-y.

Hi NaCl-y,

A few other items could affect the sharpness of your projected image:

The cellphone screen and the lens should be cleaned to remove any smudges.

The interior of the box in which the cellphone is mounted should be lined with black construction paper (or another suitable material) to minimize light reflections inside the box.

And the box should be made as “light tight” as possible to prevent stray light from entering.

Some of the DIY projectors described online use the lens from an ordinary magnifying glass (about 250 mm focal length). This type of lens appears to be of sufficient quality to get a well-focused image. If you are not using a similar lens, you might want to try this type to see if you get better results.

I hope this helps. Please ask again if you have more questions.

A. Norman

Hey A. Norman,

Thank you so much for the suggestions and for replying. I will get back on this thread if we have made any progress or improvements for our next prototype.


NaCl-y