Yes, when LCOS panels are used with lasers they can be “Focus Free.” I have found that even very technical people have a hard time believing this as it goes against one’s everyday experience dealing with “normal” light and lenses. People assume that the main function of a lens is to “focus light.” After all, people are used to having to focus a camera lens or with a projector using lamps or LED light.
The optical physics of why it is focus free would take a long technical discussion, but it has to do with the laser light being effectively infinite f-number. It is analogous to stopping a camera down to a high f-number where the depth of focus become very large.
Hopefully, “seeing is believing.” I have uploaded a couple of still pictures (click on images for larger versions) and a short YouTube video demonstrating the focus free nature of the a Laseno Projector (sold in the U.S. as the AAXA L2). This projector used a SYL2010 SVGA (800×600) LCOS plane with a 5.4 micron pixel pitch and 0.21″ diagonal.
For the top picture in this article, I projected the image the ceiling and some crown molding in my house. This ceiling has lots of angle and different depths to it and with the crown molding in the way there is some obvious depth differences. Of course with the Laseno/AAXA L2 projector, there is no focusing necessary.
For the picture on the left, I projected the image at a skewed angle from the side to cause a range of depths to be displayed. The problem you have is that while the projected image is focus free, when the laser light hits the screen it looses it high f-number characteristics and thus the camera needs to focus. By projecting the image on a flat piece of paper and shooting the picture straight onto the piece of paper I was able to focus the camera while demonstrating the focus free nature of the projector.
But perhaps the best way to demonstrate the focus free nature of a laser/LCOS projector is with a video. I shot a short ~1 minute video where I mounted the projector on a little dolly and pulled it back away from the screen. There was some shaking as I moved the projector so I stopped occasionally as I moved it it back so you could see it was still in focus. I zoomed with the video camera in so you could see the detail in the video image. Note that the camera’s exposures was locked/fixed on the starting frame, so as the image gets larger, it becomes darker by the ratio of the area so as the projector pull back the video gets a little dark.
I would recommend watching the video at 720p and in full screen to see how the focus is maintained.
Other Information on the Images
The ~2 year old Laseno projector I used for these pictures has a fixed focus lens. The image become well focused about 8″ from the projector to infinity.
The Laseno projection lens is not of high quality and you will see some serious chroma aberrations in picture as well as some spots having some blur due to the quality of the lens. Additionally the projector has “100% offset” meaning that it projects through only the top half of the projection lens so that the projector will project upward from a flat surface without having a keystone effect. Because of the offset projection, the image is best at the bottom of the image (which is from the center of the lens) at the chroma aberrations (color separation) become progressively worst toward the time.
You definitely will see laser speckle in the images. The despeckle design was low cost and done over 3 years ago and it uses frequency doubled green lasers which inherently have a high amount of speckle. Most people who have seen the AAXA L1/L2 “live and compared it to the ShowWX have said that the speckle with the Laseno/AAXA L1/L2 is less than that of Microvision’s ShowWX.