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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."
You can probably get some specifications from manufacturers, but I wouldn't really rely on them (you may for example get 8-bit grey scale, but it may be a non-linear response). WHy not calibrate it yourself: you have got the equipment. Also different models may vary slightly (some manufacturers will change components without telling you). Pay a bit more for good quality equipment, and bear in mind that for example the quality of a ccd camera depends a lot on the lens you use, and it may be better to buy greyscale equipment rather than use colour eqiupment in grey modes.
Also for image capture avoid anything that adds software artefacts (especially compression). firewire uncompressed cameras (we get ours from www.unibrain.gr, very good) are good for high framerate high res, with good Linux support.
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.
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