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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."
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.
I'm sorry to inform you but this information is illegal to discuss as it would enable you to use this device as you see fit.
Please continue to use the equipment as the manufacturer intended but please refrain from learning anything about it or using it for actual work.
Your friends in peace
USA
..which just shows that the human brain is ill-adapted for thinking and was probably designed for cooling the blood-T P
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.
It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail. - Abraham Maslow
First you can check out How Things Work for the basics.
Second, off the shelf imaging devices are challenging to use for scientific data collection for a number of reasons. The main one being their response is usually designed to replicate the human eye rather than a true spectral response--the difference between photometry and radiometry.
For resolution tests, go to www edmundoptics com and check out the various testing targets available. The cheapest mylar USAF targets are pretty good for testing spatial resolution. Remember that when you get close to the resolution limit of the CCD, aliasing due to misalignment is going to be a factor. Your resolution could be up to a factor of 2X (per axis) better than you can test for, unless you're able to align the target with the pixels.
You should also try to figure out which CCD the device uses. Yahoo!'s Electronics Marketplace is a good place to search for components and there is usally a link to the manufacuter's spec sheet. Some spec sheets are quite detailed and will give you plenty of information regarding sensitivity, dark current, spectral response, etc.
Be skeptical of resolution claims. A flatbed scanner I have claims 9600 dpi or about 2.6e-6 m resolution. In reality, it's no better than about 5e-5 m.
Also, the picture you get out vs the "real" picture is highly dependent on the imager's software & firmware. Autoexposure and color correction functions are usually present and can play havoc with an attempt to figure out what the "real" image is. Again, test targets may help here--if you can control all the other variables in the system, you can do some calibration experiments to figure out what the imager is doing to your image.
Well, I hope this points you in the right direction.
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.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
If your goal is to reduce the cost of automating experiments that require an optical sensor, then consider the imaging equipment being used by amateur astronomers. These imagers are less expensive than the "professional grade" units, and are much more adaptable to being attached to equipment than are consumer units. Most of the amateur astronomy magazines have an assortment of ads for these units. As indicated by other folks, you'll need to develop or acquire physical calibration standards for noise, linearity, sensitivity versus exposure time, resolution, dark response, pattern sensitivity, repeatability and temperature stability, to name a few. It sounds like fun. Good Luck, Art