I received concerns that the chroma aberrations (color fringes) seen in the photos in Part 2B were caused by poor alignment of the lasers. I had aligned the lasers per Celluon’s instructions before running the test but I decided to repeat the alignment to see if there would be a difference.
After my first redo of the alignment I notice that the horizontal resolution got slightly better in places but the vertical resolution got worse. The problem I identified is that the alignment procedure does not make aligning the pairs of red and green lasers easy. The alignment routine turns all 5 lasers on a once which makes it very difficult to see pairs of lasers of the same color.
To improve on the procedure, I put a red color filter in front of the projector output to eliminate the blue and two green lasers and then aligned the two red laser to each other. Then using a green color filter, I aligned the two green lasers. I did this for both horizontally and vertically. On this first pass I didn’t worry about the other colors. On the next pass I moved the red pair by always the same amount horizontally and vertically and similarly for the green pair. I went around this loop a few times trying for the best possible alignment (see picture of alignment image above).
After the re-alignment I did notice some slightly better horizontal resolution in the vertical lines (but not that much and not everywhere) and some very slight improvement in the vertical resolution. There was still the large chroma aberrations, particularly on the left side of the image (much less so on the right side) that some had claimed were “proof” that the lasers were horribly aligned (which they were not before). The likely cause of the chroma aberrations is the output lens and/or angle error in the mechanical alignment of the lasers.
Below shows the comparison before and after on the 72-inch diagonal image.
Note the overall effect (and the key point of the earlier article_ of the projected image going further out of focus at smaller image sizes. Even at 72-inch diagonal the image is far from what should be considered sharp/in-focus even after the re-calibration.
Below shows the left and right side of the 72-in diagonal image. The green arrows show that there is minimal chroma aberration on the right side but there is a significant issue on the left side. Additionally, you may note the sets of parallel horizontal lines have lost all definition on the left and right side and the 1 pixel wide targets are not resolved (compare to the center target above). This loss of resolution on the sides of the image is inherent in Microvision’s scanning process.
While the re-alignment did make some parts of the image a little more defined, the nature of the laser scanning process could not fully resolved other areas. In future article I hope to get into this some more.
One other small correction from the earlier article, the images labeled “24-inch diagonal” are actually closer to 22-inches in diagonal.
Below are the high-resolution (20 megapixel) images for the 72-in, 22-in, and 12-in images after calibration. I used a slightly different test patter which is also below (click on the various images for the high-resolution version).
Just to verify that my camera/lens combination was in no way limiting the visible resolution of the projected image, I also took some pictures of about 1/3 of the image (to roughly triple the resolution) and with an 85mm F1.8 “prime” (non-zoom) lens shot at F6.3 so it would show extremely find detail (including the texture of the white wall the image was projected onto).
Below are the images showing the Center-Left, Center and Center-Right resolution targets of the test chart above. Among other things to notice how the resolution of the projected image drops from the center to the left and right and also how the chroma/color aberrations/fringes are most pronounce on the center-left image.