Using Commodity Hardware in Laboratories?

PhysicsTom asks: "I am a Senior Physics student who's final year project is based upon using common, easily available technology to replace parts of the aparatus used in various departmental labs. Currently, my main area of interest is trying to integrate certain computer peripherals (such as scanners and digital cameras) into experiments at an earlier stage, so that images gained from the experiments (such as difraction patterns, etc) can be analysed in a program such as MathCAD straight off, rather than the much less efficient methods we're using at the moment. The problem is that I am having trouble finding out about the way in which scanners and digital cameras work, and how this would affect their accuracy with respect to what I am aiming to do." Basically, how do the various hardware aspects of such devices affect their ability to accurately measure or scan the subject of the experiment?

"The information I am looking for includes things like: the resolution of their grey-scales, what degree of accuracy the motor steps at, how uniformly distributed the CCDs are in the arrays, and other issues that might affect accuracy. Just so that I can know how close to the 'real' picture what I get out of the scanner/camera is. If anyone can tell me all these boring facts for any suchequipment (preferably solutions currently available in the UK) then I would be very appreciative."

Comments

No guarantees

[TheSHAD0W]

And the answer is... You can't depend on it. You can't even depend on one camera being identical in specs to another. These devices are made for the consumer market and aren't meant for scientific use.

This doesn't mean you can't use them, though. What it does mean is that you'll need to select something you're pretty sure can handle what you want, and then devise procedures for calibrating the devices' output.

Calibration

[Ami Ganguli]

Have you considered just calibrating the equipment? You'll probably need this anyway since, even if you can get the specs, they'll be expressed as ranges and individual components can fall anywhere within the range (as well as changing physically over the life of the equipment). This is true of your custom hardware as well.

If you want to get an idea of how the equipment performs before you buy, just bring your test images and a laptop into the store and ask to try the demo model.

Talk to some of the researchers in your lab. They probably already have tests as well as software that will compensate for irregularities in a CCD based on the results of the calibration.

Seems to me...

[sysadmn]

that the first lab, or first part of each lab, should be spent analyzing errors introduced by the equipment! That would be no different than running a control sample through a chromatograph before running unknowns, or verifying a signal generator's output before testing a circuit.
It would be a good lesson in the real world - like the old aphorism

In theory, there is no difference between theory and practice. In practice, there is.

Re:Hm, well, when I was in college...

[Anonymous Coward]

I guess a gravity bong is a good way to demonstrate PV=nRT

Good for imaging, unsuitable for measurement

[dgarant]

Consumer imaging devices are great if what you want to record are spatial patterns of light in an image or over time. But if you need to record absolute light values, or measure differences within a still image, or compare values over time, you will need a scientific measuring device capable of maintaining a calibrated black level as well as a known response to light. Consumer scanners typically only maintain a calibration within a single scan cycle, then recalibrate for the next scan, in order to give consumers the best digitization for each individual target. Consumer photo and video CCDs let the black level 'float' over time so as to give the best overall exposure at any given instant. These design features make consumer equipment useless as measurement devices, but ideal as pattern recorders.

Hear hear!! (Too late to change your topic?)

[coyote-san]

Not only do I agree 100%, I would put it even more strongly.

Stop thinking like a freshman who expects to find the answers in the back of the book. Even if you find this information someplace, the nature of commodity (vs. scientific) gear is that the manufacturer can change it at any time to meet market needs.

You're a senior and need to start thinking like one. If you need calibration data, and you do, you should be thinking about how to get it for yourself using other commodity equipment. This is important today, critical with the improved hardware a decade or two from now.

A trivial example I would have killed for 20 years ago? A 600 DPI laser printer. With it you can easily produce high quality optical test patterns, including some basic grey scales. (A standard sized sheet of paper will have far more 'pixels' than the CCD element in the camera.)

A slightly more advanced example is what you can do with a cheap A/D card. 10-bits of accuracy doesn't sound like much, but if you're clever you can leverage it.

Finally, I would strongly recommend that you review the "Amateur Scientist" columns in Scientific American over the past four or five years. If you can construct a simple closed feedback loop (cheap op-amp chip) and monitor it with an A/D converter ($100), you can do some incredible experiments.

Drivers are highly suspect.

[JabberWokky]

Whatever you use, open source drivers are a very very good idea - the Windows drivers for many scanners (and I would guess for the digital cameras as well) process the images to "clean" them - remove artifacts like the glimmer in tight lines, etc.

Artifacts from CCDs are bad enough - you don't need more caused my "corrective" software designed for human perception.

--
Evan