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  1. #21
    Photo Engineer's Avatar
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    Basically a microdensitometer is a regular densitometer recalibrated to have a high intensity beam with a small aperture. It must be smaller than the smallest line you wish to scan. We typically used 1000, 100, 10 and 1 micron lines.

    Usually, 10 microns is small enough, and therefore a 1 micron or 0.5 micron aperture would be OK.

    PE

  2. #22

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    Objects 3-4 microns can be measured with quality optical microscope, this is about the size of grain clumps I believe,but it sounds expensive.
    http://www.microbiologyprocedure.com...icroscope.html

  3. #23
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    Grain clumps are smaller, and appear as noise in photomicrographs of edges. This is how RMSG is calculated, by analyzing the noise.

    PE

  4. #24

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    By all means get yourself a better microscope !
    The type depends on what you want to see: butterfly wings can be seen with low magnification, filmgrain at verry high.
    I know this is a bit on the side-line of this forum, but still, you can allways send me a personal message.

    Good luck !
    Peter

  5. #25
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    This is a little off topic, but about 15 years ago I know a rather brilliant fellow who was making an electron microscope the size of a sugar cube as his doctoral thesis. At the time it blew my mind that it was so small. I can only imagine the size they can make them now!

  6. #26

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    Quote Originally Posted by David Foy View Post
    Scientific American published instructions for making an electron microscope at home. Martin Gardner's column, I believe. Check the indexes from 30 to 40 years ago.
    Most likely "Amatuer Scientist" and not Martin Gardner.

    I happen to have all the Amatuer Scientist articles on CD - it was $30 at Fry's several years ago and I could not pass that up. I have a whole basement full of Scientific Americans, most every issue from 1950 up to 1990.

    It's September, 1973 - "A High School Physics Club Builds Electron Microscopes" and has a difficulty level of "4 - possibly lethal"! I wonder what level 5 is - "may blow entire world"?

    It's a transmission electron microscope. it will take some glass-blowing, a good vacuum system, and it has a nice vacuum tube power supply.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  7. #27

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    I looked into having a friend of mine TEM my samples, if I ever made any worth while (which I have not- yet).

    The local machine is for rent at $175 per hour, and apparently he'd be stretched to do 3 an hour (maybe up to 7 if he was doing a bunch, but apparently set up time takes a while, something about a perfect vacum and charging the flux capacitor) On the flip side, the TEM at the local U is used for taking pictures of bucky balls and nano tubes, so I'm pretty sure it could fill a frame with a halide crystal if I wanted to.

    PE, if you have time, it would be useful to know the specific issues of preparing an emulsion sample for a TEM, since at some of us might hand samples of to the local universities for grain portrature, and it'd probably be advantageous to also hand a list of things to watch for when preparing the sample. (I'm assuming that no one here is actually going to try to run one themselves, the Nano geeks I know spend about 2 weeks on how to learn the machine badly, and it apparently takes months to learn how to use it well)

  8. #28
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    I've never done TEMs, just SEMs and EMs. The prep method requires making a carbon replica. That should be enough for your friend to get started. You make the carbon replica of the crystal, and then use about the same conditions as for the buckyballs.

    PE

  9. #29

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    I took a class in college in the mid-80s and it was on operating electron microscopes, both TEM and SEM. You can also make chrome replicas of items in addition to PE's mention of carbon replicas. That involved coating the subject/object with a plastic film, peeling/removing the film from the original, and then sputtering chromium metal at an angle onto the plastic replica. It was put on at an angle so that it cast a "shadow" of the object. The plastic was then removed by dissolving it with solvent. The chrome replica was then mounted in a frame and placed into the TEM.

    SEM was much easier - the object was sputtered with silver metal and then it was placed into the SEM. The silver was there to allow the electrons to disappate from the surface of the object otherwise it could become charged and then it would repel the electrons the SEM shoots at it.

    How you make replicas objects on the scale of film grain, I'd like to know. Put a thin coating of the emulsion onto glass and then sputter carbon onto it, and then dissolve the emulsion back off the carbon?
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  10. #30
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    Electronic microscopy seems to have evolved to such a degree that even a company as Agfa contracts work of that kind to universities due to the sophisticated hardware to be found there.

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