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Pesky diagonal lines on a custom CRT challenge designers

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WKetel
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re: Pesky diagonal lines on a custom CRT challenge designers
WKetel   10/2/2010 12:48:15 AM
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A similar system was used to produce printing plates, although I believe that it was done one character at a time. This must have been in about 1982 or 1983. It was much faster than the previous mechanical system, and a great deal more flexible. The other place that stray magnetic fields cause problems is electron microscopes. It seems that they can detect very small changing magnetic fields, leading to the creation of some quite interesting magnetic field detecting instruments. The result is an awareness as to just how much electromagnetic noise we are constantly bombarded with. It is there, it is just hard to see.

tomkinsr
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re: Pesky diagonal lines on a custom CRT challenge designers
tomkinsr   10/2/2010 12:30:19 AM
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I worked for Dipix Systems Limited for a number of years. We sold a number of similar units as output devices for our Digital Image Processing systems. From what I recall, the unit had a precision CRT from Tektronix inside. The devices were very good at imaging data, on Polaroid and film up to 8 x 10 with just marvellous results. Most of our customers were processing Landsat satellite data, some microscopy, some aerial and some military satellite data. I seem to recall the units we sold had an HP-IB interface. We also sold a flying spot scanner to one customer.

CharlesGlorioso
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re: Pesky diagonal lines on a custom CRT challenge designers
CharlesGlorioso   10/1/2010 11:47:20 PM
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Hi Asho, The short answer is accuracy and precision. A traditional TV raster scan has the horizontal axis free running in resonant mode. This is very energy efficient, but produces scans with significant and uncontrollable linearity issues. So we addressed every pixel in x and y and got position accuracy equivalent to our dot size. We still got the benefit of the phosphor persistence, since the camera shutter was always open, it collected light from an illuminated spot after the illuminating beam had moved on. However, we did create reciprocity failure in the film by scanning slowly, and had to correct for that in setting our exposure levels.

David Ashton
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re: Pesky diagonal lines on a custom CRT challenge designers
David Ashton   9/28/2010 8:46:20 PM
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Nice story, Charles. But could you tell us why you had to work one pixel at a time, rather than doing a complete raster scan or multiple scans (obviously it would have to be a complete number of scans) and making the phosphor persistence work for you to reduce the time of a scan?

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