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  1. #11
    Photo Engineer's Avatar
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    Yes, it can be simpler as you say.

    I mention above a 3 stripe chart with a 21 step scale behind it which can give you relative speeds of a film at 3 different wavelengths (RGB) once you calibrate it.

    PE

  2. #12

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    Quote Originally Posted by Photo Engineer View Post
    This harmonic vanishes with a UV filter and is one of the faults of these particular instruments.
    It's not really a fault, it's just a function of using a diffraction grating. A spectometer using a prism will not have this issue. Prisms have their own issues...

    I bought a 4 inch spherical mirror with a diffraction grating on it to make one of these. Someday I'll do it!

    Colored LEDs should be an easy way to calibrate any spectrosensitizer now that red, green, blue and even UV LEDs are readily available.

  3. #13
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    Yes, as you say Kirk.

    We have big instruments at EK without this problem. They are used for major work.

    PE

  4. #14

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    In the 1960's I worked for a company that produced spectrometers. For most purposes we supplied xenon lamps as the light source. I do not remember the range thes lamps cover but we normally worked with the uv and the near uv regions. All mirrors were first surface. All the lenses and windows were quartz or equivlant. Most calibrations were done using varions compounds that had known adsorbance lines or floursed (spelling) at known wave lengths. Most of the equipment we produced was used in research labs, either in universities or medical research labs.

  5. #15
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    Some talk and inklings of a DIY spectrosensitometer from 5 years ago; did anyone ever get around to doing it?

    So let's break down what the optical path might look like. It's hard to tell from the diagrams what exactly is happening in the 3rd dimension.

    So we have a light source and a lens (simple meniscus?) to concentrate the light onto a slit. The slit will presumably create a thin "bar" of light that next must go to a diffraction grating. I think the "science class" type gratings that are mounted in 35mm slides would be ideal, as has been noted above.

    Now, does the angle of the grating affect how the light is diffracted, and how much it fans out?

    How important is the collimator in front of the grating? It looks like the purpose of that is to get the light to come at it perfectly parallel. But wouldn't a horizontal bar of light (from the slit) hitting the grating still make a reasonable projection of the spectrum?

    Then the diffracted beam of light encounters the step-wedge, placed in front of our test film.

    What I'm having trouble imagining is the interaction between the projected spectrum and the step wedge. Most step wedges that we know are arranged in a long thin strip, not wider than a centimeter or two. How on earth are we supposed to project the spectrum onto this and achieve a 21-step gradation at all spectral frequencies? We need each spectral region (400, 500, 600, etc.) to go through the whole range of steps. This seems obviously impossible with the thin step wedges that we're all used to.

    Now, Kirk, you say you have a spherical mirror with a grating in it; how would that design work? It sounds like that would be fundamentally different from the above diagram posted by Emulsion.

    Thanks all,
    If you are the big tree, we are the small axe

  6. #16

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    Hi Holmgurgers,
    Now that several people are seriously looking at sensitizing dyes, in the words of an old New Yorker " It can't hoiht." I would like to be able to look at the spectrums of my emulsions. It comes down to the cost of such a spectrometer.
    Someting that I have not tried, but your post brought to mind. Shooting color charts through cut off filters may be more informative than just shooting the color charts in sunlight.
    Bill

  7. #17
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    I agree Bill.

    I'm sure that color charts and just shooting the film and interpreting the results can be informative, but not nearly as illustrative as a wedge spectrograph. A series of those can be compared against each other almost immediately, and without much deduction. Their look says it all.

    I'm convinced we can make something very inexpensively. All we're doing is projecting a spectrum onto a piece of film, through a step wedge. It's just a matter of buttoning it all up and working within some parameters.

    First though, I think we really need to wrap our heads around the design and understand that (in 3 dimensions) more clearly. Hopefully some Q&A will get us there fairly quickly.
    If you are the big tree, we are the small axe

  8. #18
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    How about buying a set of LEDs at different wavelengths and soldering them side-to-side? I know, it's not perfect, but it would be easy. The set could be: IR, 660 nm red, 625 nm bright red, orange, yellow, traditional dim yellowish-green "green", high-brightness 520-530 nm green, blue-green, blue (470 nm), deep blue (450 nm), UV (405 nm). Add trimmer pots to every LED and calibrate using a commercial panchromatic film with a known, published sensitivity curve.

  9. #19
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    Someone posted the name of a company in Buffalo that makes inexpensive monochromators. I did not save the information as I already have one! Sorry. However, IIRC, they ran under $50.

    In my unit, it is a fully straight line path from the light to the "output". The monochromator has an opening and is box like with an opening on exactly the other side for the exit beam. There are probably many twists or turns inside the "black box" but I am loathe to open it. It works you see. So, what ain't broke, don't try to fix.

    There are 2 photos of the unit in the book and a sequence of the unit in operation in the DVDs.

    PE

  10. #20
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    A brilliant idea, but I'm going to say that personally, I think it's too much trouble... at least, it's certainly outside my abilities.

    I'm gonna be thinking in terms of the above design (the diagram), with a simple halogen or tungsten bulb. It's the optical path that I really wanna get a grip on.

    edit: Thanks PE, gonna have to look for that Buffalo co.
    If you are the big tree, we are the small axe

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