Finding Uniform Focusing in Flexible Fresnel Lenses

[huguchosli]

Well this thread title sucks, sorry. << Mentor Note: Title Edited>>

I have a plano convex lens (actually equivalent stack of two fresnels each with focal length 120mm, groove pitch: 0.3mm).
If I put a photo behind it at a 45mm distance and view through the lens from a 12mm distane, I get perfect focus in the middle area.

I am able to correct the spherical distortion by adding a pre-distortion to the original printed photo in photoshop.

Similarly I can reduce the chromtic aberration in a similar way.

What I can't do is get things on the edges in focus as well.

The lens is flexible and bendable.
So is the material the photo is printed on.

What kind of geometic distortion should I apply to the fresnel lens and the photo frame to achieve uniform focusing?

I am picking up where these researchers left off. http://www.cs.ucsb.edu/~mturk/pubs/IsmoICAT-EGVE2016.pdf

The bending of the lens as illustrated in that research paper seems the ideal fresnel lens bended shape to me, that is, if they also bent it in the other axis.
https://i.imgur.com/WKw35Y3.png

https://i.imgur.com/YgQq3Kv.png

https://i.imgur.com/JSb7fjd.png

The original authors seem to have disregarded actual optical distortion and went with trial and error and (quoting) "good enough" results.

Even though we do not have the technology of custom shaped screens (not just bendable in one axis at a time) and may not ever, this can still be used for a full FOV stereocope ( https://en.wikipedia.org/wiki/Stereoscope ). I am not aware of one existing to date.

I could write some software in Python to take stereo data and convert it to properly pre-distorted frames to be printable on a vacuum formable photo frame sheet. The thin fresnel lens are also vacuum formable and simply bendable. So anyone wanting their own complete FOV stereoscope can build one for very cheap. Seems fun but the optical distortion calculating part for achieving uniform focus is beyond my expertise, if anyone wants to chime in with a distortion/3d shape for the fresnel lens and photo frame, that would be awesome.

 

[eljose79]

Hello,

First of all, I appreciate your enthusiasm and interest in this topic. As a fellow scientist, I can understand your frustration with the trial and error approach used by the original authors in their research paper. However, it is important to note that sometimes, in science, we have to start with "good enough" results and then continue to improve upon them.

In terms of achieving uniform focus, there are a few things to consider. First, it is important to understand the concept of depth of field. This is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. In your case, the depth of field is affected by the distance between the lens and the photo, as well as the focal length of the lens. So, to achieve uniform focus, you may need to adjust these parameters accordingly.

Additionally, the shape of the lens and the photo frame can also play a role in achieving uniform focus. As you mentioned, the bending of the lens can help correct for spherical distortion, but it may not be enough to achieve uniform focus. In this case, you may need to experiment with different shapes and curvatures of the lens and the photo frame to find the optimal combination.

Another factor to consider is the refractive index of the material used for the lens and the photo frame. This can affect the way light bends and passes through the materials, which in turn can affect the focus of the image.

In terms of the distortion/3D shape for the lens and photo frame, this would require some complex calculations and simulations. I would suggest consulting with an optical engineer or a specialist in this field to help you with this aspect.

In conclusion, achieving uniform focus in this setup may require a combination of adjusting parameters such as distance, focal length, and shape, as well as considering the refractive index of the materials used. I hope this helps and I wish you the best of luck with your project!