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  1. #21

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    Hi hrst,
    Your idea is workable assuming the "technician" who assembles the thing has at least one hand which is in some way connected to his brain. I fear that I would solder each LED to one of my fingers. I think that I may look into PE's source for a $50 ready made thingamajig.
    Bill

  2. #22
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    At EK we used an R/G/B filter combination to mimic a spectrosensitometer to judge the relative speeds in the 3 regions of the spectrum. It worked just fine. I build one when our old one wore out. And, I had to calibrate it!

    PE

  3. #23
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    On page 175 of this book is the basic outline of a DIY spectroscope for telescopes. It could be easily adapted to photography methinks.

    http://books.google.com/books?id=XDE...oscope&f=false
    If you are the big tree, we are the small axe

  4. #24

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    Hi All,
    Holburgers,
    Your diagram scares me! "Simple" to you maybe. I'll bet you were one of those nine-year-olds who built his own rockits,radios and computers.
    PE,
    Any chance that you could sketch a crude diagram of your tri-filter gizmo?
    Bill

  5. #25
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    Well, Bill, I have posted a picture and a diagram here before. I tried and cannot find the picture I posted, but it was the one used in the book and I have "retired" them all since the book's completion. I can repeat the diagram here in text.

    Constant voltage > Light > shutter > Monochromator > step wedge.

    The input to the electronic shutter is a precise timer. The whole optical path is on a heavy metal plate to keep it in alignment. It is nothing fancy and could be cobbled together by anyone. A prism or diffraction grating could work. It is all straight line from one end to the other, and about the length of a counter top (~24") and about 10" wide.

    PE

  6. #26
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    Okay! How about this;

    I ordered some surface-mount LEDs from Ebay/China, the wavelengths I am missing. Unfortunately, they always sell at least 10 to 20 pieces, whereas I only need one of each . And I have hundreds or thousands of some wavelengths already.

    I happen to make PCB's all the time and it would be wasteful to make just one of those tiny little boards. So, I will make several of them at the same time. And once I need to calibrate mine, I can just apply that calibration to all of them. I am thinking about fixed resistors.

    So, those will be tiny little units with a series of LED's: for example, IIRC, 660, 625, 600, 580, 550, 520, 470, 400 nm. As they are LED's, they are not sharp but show some response to +/- 25 nm so there is a bit uncertainty there, and the calibration won't be perfect either, but at least it will be cheap, small (something like a credit card) and simple and quickly done. It will need some kind of diffusor, but I have a solution for that ready too. It will work from a 9V battery and cost something like 5-10 USD.

    I can include a simple timer to the design with practically no extra size or cost.

    Anyone interested? What about the dimensions? I was thinking the LED "bar" could be something like 5 cm (2") long.

    I will build this one for myself anyway and this is easy to "mass produce" in a range of 1-10 units.

  7. #27

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    hrst,
    Yes , for such a price, or a little more, I am absolutely interested. Anything I do not have to build myself. I have built things from wood, glass and plastic. But never anything involving wires and solder.
    Bill

  8. #28
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    hrst,

    Maybe you could stack them in a grid... 10 LED's of each frequency for example. Use fixed resistors to attenuate each LED a little more than the one above to it to create a wedge of that part of the spectrum. Then maybe with a dozen stacks like this...

    Use a few more components this way. But you wouldn't have to place it on a dozen Stouffer scales.

  9. #29
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    Bill;

    If you turn the wedge 90 degrees, you only need one step wedge. It has to be wide enough for the entire spectrum though.

    PE

  10. #30
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    hrst, I would definitely love to get my hands on such a gizmo. Looking at your past electronics skills, I have no doubt you can make one! Nevermind my previous neigh-saying...

    Ok, so attached is a depiction of a typical step wedge like we all use (Stouffer), and then an ideal form for a spectrosensitometer. We need something that's more "squat". Hamburger as opposed to hotdog... if you will. Right?

    Now why is a thin slit so important? That spectroscope article suggests that it should be 2-10 mils wide. Why does the light have to be collimated exactly?

    I've found 500 lp/mm and 1000 lp/mm diffraction gratings on eBay for very cheap; like the attached image. I think I'm going to just have to buy these and play around with them to see how they act in different circumstances. Again, in every diagram the diffraction grating or the focusing lens is oriented at an angle; is this the only way to get the diffraction grating to "do its stuff"?, that is, to spread out an image of the spectrum.

    It'd be ideal to use plastic lenses so that we don't alter our UV transmission much. Cheap acrylic lenses abound, in all different types of powers.
    Attached Thumbnails Attached Thumbnails step wedges.JPG   diffractiong rating.JPG  
    If you are the big tree, we are the small axe

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