Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,566   Posts: 1,545,427   Online: 1057
      
Page 5 of 6 FirstFirst 123456 LastLast
Results 41 to 50 of 52
  1. #41
    holmburgers's Avatar
    Join Date
    Aug 2009
    Location
    Rochester NY (native KS)
    Shooter
    Multi Format
    Posts
    4,420
    Images
    2
    I think a step wedge is important. Any kind of "dynamic" exposure (where it has to be moved manually) is going to be really troublesome methinks. It's going to destroy the whole continuity of having an identical-looking pattern that can be easily compared to others at a glance.

    I also think you should consider switching from a Rick Astley song to, say, an Oingo Boingo song. Thoughts?
    If you are the big tree, we are the small axe

  2. #42
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,306
    Images
    46
    I think holmburgers is right moving the device would be hard, and make it less reliable.

    But I agree with PE, if I understand the idea, a grid pattern to outline where you are looking sounds like a good idea.

    I still like the fixed resistors to calibrate and multiple LED's of each wavelength idea. If necessary you could make different ones blink a specific number of times but there would be intermittency effects.

    How about, keeping it credit card size but spread the small spots out so they are unlikely to interfere with each other. At regular intervals place a white LED to provide a benchmark grid.

    Might as well add a "white" LED column as well to provide for exposure test - even if it is not sensitometrically perfect light it may add to the usefulness.

    As PE said, you really need to go to DMax so 10 full stops of exposure range from dimmest to brightest (or shortest to longest exposure).

    I am intrigued by the possibility it can be done without a Stouffer scale, with the LED's in direct contact with the emulsion. Then you don't have to make a diffusion chamber or other manufacturing invention. It can be a bare surface mount electronic device with one part and a battery. I almost want to recommend using a "123" battery. They are not uncommon these days and provide a good amount of 3v power.

  3. #43
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,035
    Images
    65
    Bill;

    There were small desktop spectrosensitometers all over Kodak Park at one time, along with the big units for precise work in B-30 and B-57 for film and paper. IDK what happened to them. Results using them are found in Haist, Mees and also in my book.

    PE

  4. #44

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by holmburgers View Post
    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.
    Sorry for taking so long to get back - I'll had a bad cold the last week...

    Yes, a spectrometer with a mirror (by using a reflection grating) does have quite a bit different layout than one that uses a transmission grating. The reflection gratings, both flat and with curvature, make spectrometers that can be more compact then transmittion gratings as the light path can fold back over itself.

    The reason I found a spherical reflection grating is that I was going for a design that's called a "Rowland circle spectrograph". With a Rowland circle spectrograph, if the inlet slit and the grating all lie on a circle, then the diffracted spectrum will also lie on the same circle. The diameter of the circle equals the radius of curvature of the grating blank. So if the circle is large, then you can make a pretty big spectrogram with no extra lenses or mirrors.
    See:
    http://gratings.newport.com/library/.../technote3.asp

    The drawback is that if you have to use film to measure the spectrum, then you need film that's on a flexible support, like paper or acetate. I was looking at testing variable contrast papers at the time that I bought the mirror, so that would not have been an issue. Glass plates would have been a bit of a problem...

    I also bought a flat relection grating as well, just for fun and in case I wanted to use plates.

    I was going to use colored LEDs as a way to light sources to calibrate my spectrograph, but I like the idea of using LEDS at various wavelengths to make "spot tests" at those wavelenghts by contacting emulsions directly on the LEDs. I like the idea of making an array - "columns" of various wavelengths and then "rows" at differing light intensities.

    One thing to think about is that LEDs can have fairly wide emission spectra - some designs like "superirradiant" LEDs are a bit more like LASER diodes and have more narrow spectra emision.

    Side note, my second year physics professor at Reed College in 1983 told that class that if any of us figured out how to make a commercially viable blue LED, we would be rich! Too bad I dropped out of that class before I had a clue about how to make a blue led... (Well, I knew, you had to make a diode with a higher energy gap). Now I see that someone started selling blue LEDs in 1989.
    Kirk

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

  5. #45
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,035
    Images
    65
    But good, durable blue LEDs just recently (Blue Ray).

    PE
    Last edited by Photo Engineer; 06-27-2012 at 07:26 PM. Click to view previous post history. Reason: spelling as usual!

  6. #46

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by holmburgers View Post
    Some talk and inklings of a DIY spectrosensitometer from 5 years ago; did anyone ever get around to doing it?
    Still on my list to do someday...


    Quote Originally Posted by holmburgers View Post
    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.
    The image of the slit continues on through the spectrometer unless it gets blocked out. So the projected image with the spectrum will be as tall as the slit.


    Quote Originally Posted by holmburgers View Post
    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.
    Those cheap, 35 mm slide diffration gratings are typically not very efficient. A "replica" grating is going to be a better solution than the cheap holographic ones. Best are original or master ruled gratings, but who can afford those?

    Quote Originally Posted by holmburgers View Post
    Now, does the angle of the grating affect how the light is diffracted, and how much it fans out?
    Yes, the ruling angle controls the angle of diffration, The more lines per inch or mm controls the range of wavelengths that can practically be diffrated. Replica gratings will have the same diffration angle as the ruled grating that they were copied from.


    Quote Originally Posted by holmburgers View Post
    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?
    Collimated light will give a sharper image of the spectra. If you have your light source a LONG ways away relative to the dimensions of your spectrograph, then you would not need a collimator. If your light blulb is right next to close to the slit, then you will definitely want to collimate the light source.


    Quote Originally Posted by holmburgers View Post
    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.
    As I said above, the image of the slit will project though the spectrometer unless it is blocked by something. It's hard and expensive to get gratings of any great width, so you want to maximize what you have going through the spec.

    I was planning on getting a centimeter or two at the most of spectra. So I was going to make multiple exposures on the film/paper at various light intensities to get the spectral info for the film. To change the intensity, I was planning on keeping the exposure time at 1 second, and then using Wratten ND filters between the light source and the slit. Since I can measure the spectral characteristics of the Wratten ND gelatin filters with a spectrometer that I have (or look them up online as Wratten/Kodak publishes this info) then I could apply a correction to my measured spectrograms.

    Scan through this book - it's pretty good and has all the math and more that you'd need to calculate anything with gratings.
    http://gratings.newport.com/library/handbook/toc.asp
    Kirk

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

  7. #47

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by Photo Engineer View Post
    Bud good, durable blue LEDs just recently (Blue Ray).
    Blu-Rays use LASER diodes at 405 nm - funny thing is that is considered a "violet" wavelength!

    I see Sony unvieled a Blu-Ray prototype in Oct. 2000 - I'm not sure when the diodes were invented, but it's certainly a few years before they showed the Blu-Ray.

    Speaking of random LASER devices, here's something I plan on making some day - a Laser Harp:
    http://youtu.be/sLVXmsbVwUs

    I love when the laser fans out after first being powered up!
    Kirk

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

  8. #48
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,035
    Images
    65
    That harp reminds me of the sound track from Forbidden Planet!

    Actually, I knew of the difference between the blue LED and the blue Laser, but they were both slow coming to fruition due to longevity issues and other problems.

    PE

  9. #49

    Join Date
    Oct 2006
    Shooter
    Medium Format
    Posts
    131
    Quote Originally Posted by Kirk Keyes View Post
    Yes, a spectrometer with a mirror (by using a reflection grating) does have quite a bit different layout than one that uses a transmission grating. The reflection gratings, both flat and with curvature, make spectrometers that can be more compact then transmittion gratings as the light path can fold back over itself.
    I see. In that case you could optically contact (index match) a transmission grating to a mirror.

    By the way, what about simply use a CD, DVD, Bluray disc as a grating, wouldn't that be an option?




    Quote Originally Posted by Kirk Keyes View Post
    One thing to think about is that LEDs can have fairly wide emission spectra - some designs like "superirradiant" LEDs are a bit more like LASER diodes and have more narrow spectra emision.
    Yes. In my opinion LEDs are probably too much broadband for such an application. Lasers might be far better for "callibration". Lasers at 405, 445, 532 and 650 nm have become very affordable...

  10. #50

    Join Date
    Oct 2006
    Shooter
    Medium Format
    Posts
    131
    Quote Originally Posted by Kirk Keyes View Post
    Yes, the ruling angle controls the angle of diffration, The more lines per inch or mm controls the range of wavelengths that can practically be diffrated. Replica gratings will have the same diffration angle as the ruled grating that they were copied from.
    Speaking in "holographics" the number of lines per mm is called spatial resolution. The higher the resolution the larger the angle between the input and the output (the diffracted) beam.

Page 5 of 6 FirstFirst 123456 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin