Some things to help you understand:
A Galvo Scanner... Image from Cambridge Technologies web site. This is a high end device, typically used for laser based machining, not an inexpensive one.
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The next image is two galvos with mirrors in a scan head, this lets you do X-Y deflection, taken from the Scannermax web site,
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The third image is conceptually what is going on.
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The fourth image, is a oscilloscope screen shot of the position feedback signals from a high performance scanner pair, showing you the movement occurring behind a projected image.
Note the bright spots and some overshoot at the corners, this is a well tuned and accurate scan pair, projecting the standard test pattern at 60KPPS (Image Laser-FX.com, probably taken by L.M. Roberts) . The forth image is the same thing as the eye sees it, with the laser gated on and off as needed. The image is not geometrically corrected, as a test was going on at the time, for something else. The image is about 15 years old, and things are a lot better now. This is a multiple exposure trace of the position signal, its a bit blurry from filming off a scope screen. See where it dwells at the corners? This is the software adding a correction so you see a sharp right angle projected. This is without the "retrace" being blanked. The retrace is the mirrors moving to the next projected position.
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The fifth image is the same test pattern, but projected by a different system, in Laser, so you can see the difference between what goes on "Behind the scenes" with the mechanical motion, and what actually happens on the screen.
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The green Ilda Test image is shot on a pair of hand made galvos, by a brilliant technologist who's screen name is Elm Chan, if home made galvos and home made scanner amps can do that, imagine how sharp a good modern system can be.
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The sixth image is what you would get, in terms of overshoot, if you scanned an image direct from a CSV without correcting for galvo characteristics in software, or without "pulling points".
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The seventh image with the red bar, shows tangent distortion, which is a curve that occurs naturally any time a mirror on a shaft is used to scan light. This is one of the things we correct for in software. It does not affect the center to outer two thirds of an image much, but it does catch the outer edges at wide angles. Easily corrected for in modern software. Your seeing a raw, uncorrected image there.
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edits done, I need to get back to work.
!
Steve
Last edited by mixedgas; 05-31-2017 at 11:15.
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...