Where the PDAF sensors are...

Started Dec 15, 2011 | Discussions thread
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Helen
Helen Veteran Member • Posts: 7,146
Where the PDAF sensors are...
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Thought folks might be interested in this image. I was messing around with the 30-110mm lens last night, and happened to take a shot of the TV screen. When I examined the shot, I saw something interesting. On the attached image, I have (messily) highlighted the ends of the lines to aid visibility, because, even magnified to the largest size that DPReview allows, these do not show as clearly as on the original.

Basically, there are nine evenly-spaced horizontal lines on the image which are symmetrically arranged (if the yellow end markers I added indicate otherwise, it's only due to the difficulty I had seeing the lines in the program I used to edit the image) - and the top and bottom ones are shorter than the others. I am 99.9% sure that these indicate the positions of the phase-detect AF pixel arrays on the J1's sensor (which are not capable of image capture). These lines do not normally show in images, but something about the moving image from my LCD TV caused them to be visible, presumably because that something made it difficult for the image processing in the camera to accurately clone them out of the image as it would normally do - it's mis-guessed the colours to use. I took several shots and the lines were always in exactly the same place on each one - of course, I took normal shots of other subjects (i.e. not LCD screens!) afterwards to verify the lines were not something that would appear in every shot for some reason and in those subsequent shots, the lines were totally invisible, as the designers intended.

Whether this pattern is observable by photographing any LCD screen, I haven't checked. Visibility may vary according to the spec of the screen photographed and the TV system it's displaying - its visibility even varies according to the program you view the image in, but it is there, it's not an artefact. NB - these lines can only be seen if the TV image is photographed close enough (or with a powerful enough telephoto setting) to clearly resolve the screen's pixels - this seems to be what confuses the image processing into leaving the PDAF lines somewhat visible.

Anyway, I just thought it was intriguing to see where the PDAF sensors live...

Nikon 1 J1
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