Blue is a lower-pitched color?

Although I am no luddite, I tend to respect and keep machinery that has proven itself (software too) rather than throw it out simply because it has gotten old and other things have come along behind it.

My scanner is a UMAX flatbed UC630, a dinosaur from the days of the three separate passes color scanning technique. So I lay an image down and it does a “red” pass, a “green” pass, and a “blue” pass, in that order.

Which brings me to the QUESTION – why the heck does the hum that it gives off sink a full major 7th (just shy an octave) and get louder when it comes to the blue pass? I should mention that before I owned a scanner of my own, my girlfriend of the time had purchased one for her artwork, and it did exactly the same thing despite being of a different brand.

This is a complete guess, but for what it’s worth -
All scanners use an illuminating light and an array of light sensors to digitise the image. The scan isn’t continous - the scanner moves, stops, scans a “line”, moves again, stops, scans another line, etc. The stops are very short so the scanner seems to move continuously. The sound is made by whatever mechanical system is periodically interrupting the movement of the scanning array.

In a three pass scanner, it may work by using the same light sensors for each colour but physically flipping a red, blue or green tranparent filter in front of the array for each pass. Or switching between red, blue or green lamps. Something like that anyway.

The sensor array won’t have equal sensitivity to all colours. It’s possible that when doing the blue scan, the scanner has to stop at each line position for a little longer which will lower the pitch of the travel mechanism.

Now you can blow my pet theory out of the water by telling me the blue scan takes less time to do…

And here I was all set to post that light in the blue portion of the visible spectrum is of higher frequency than green or yellow or red, and that blue light would therefore, by analogy with sound waves, be considered high-pitched light…

Never mind.

me too MEB

My WAG:
it could be that the method used to create the blue scan light caused this noise just like some floresent bulbs (well actually ballests) cause noise.

Well, the three passes each take the same amount of time. I haven’t timed them with a stopwatch or anything, but the blue pass is definitely not distinctively slower (or, for that matter, faster) than the prior two passes.

So much for speculation!

k2dave made a plausible suggestion. Can you see how the illuminating light is generated? Does the light source change colour between passes?

I’ll let you know. I’m under the impression that the light source does indeed change for each pass, but I admit I’m not sure. I assumed that it was and was wondering why the heck making blue light for the blue pass would result in a different pitch than doing the red and the green pass (with red and green light respectively, I assume).