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  1. #1

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    Spectrosensitometer

    PE,

    Hope you can help.

    A while back you mentioned that you used a spectrosensitometer to test sensitivity of emulsions to various wavelengths of light.

    Can you recommend a "low budget" spectrosensitometer? Can you point me towards a typical setup or photos of a film spectrosensitometer?

    Thanks From,

    Emulsion

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    1 constant voltage power supply
    1 light source with a repeatable daylight type output
    1 Bausch and Lomb monocrhomator
    1 step wedge as wide as the output of the monochromator
    1 solid mounting plate

    That is the high end.

    The low end is a strip of Wr 99, 98 and 70 filter mounted over a step wedge. Exposures will show relative R/G/B speeds. This is not quantitative.

    PE

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    Interesting ... that would be a fantastic piece of equipment for emulsion making.

    How are those parts put together to be functional?

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    The above should include a shutter mechanism and timer for achieving different exposures.

    It is linear as follows:

    Light > Shutter > Monochromator > Step Wedge / object being tested.

    The optical items are all mounted on a flat plate of metal for a sturdy makeup and to give optical alignment. The monochromator has a range from about 300 nm - 900 nm with an adjustment for which range - ie UV, visible or IR. It also has a filter drawer next to the shutter for any desired filter combination.

    I have posted examples here of exposures. I have no good photos of the device itself.

    PE

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    PE,

    Thanks for your reply. Your answer inspired me and I found that I already had the answer in no less than three photography books (I should have looked before I posted!). One being the 1958 edition of the Ilford Manual of Photography. Attached is a scan from this excellent book showing a spectrograph. Baker also has construction details for one.

    Diffraction gratings and lenses can be purchased very inexpensively from "The surplus shed". http://www.surplusshed.com/

    These companies sell step wedges.
    http://www.stouffer.net/TransPage.htm also http://www.tiffen.com/Kodak%20Profes...%20catalog.pdf

    Any recommendations on the part number of the step wedge that would be most suitable?
    Attached Thumbnails Attached Thumbnails Spectrograph.jpg  
    Last edited by Emulsion; 10-27-2007 at 04:14 AM. Click to view previous post history.

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    You have seen examples of wedge spectrograms that I posted here. There are many in the book by Mees and James, done by Paul Gilman.

    You must calibrate it somehow.

    PE

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    Wow, that looks fantastically simple ... it's one of those "Why didn't I think of that?" kind of things.


    I think I might build one.

    What is involved in the calibration? I'm assuming you'd need to somehow correct for the spectrum of the light source? I know that you'd also probably have to mark off the wavelength scale, but that'd be easy with, say, a fluorescent lamp.

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    Yes they do look straightforward to construct. Everything is more difficult in the doing though....at least for me :-)

    PE raises a good point regarding calibration.

    I understand that a fluorescent light source would have many spectrum lines in it. See the picture of a fluroscent light spectrum at:
    http://www-astronomy.mps.ohio-state....pec/index.html

    Baker has some paragraphs on calibration in Photographic Emulsion Technique, 1948 edition. He mentions using an arc lamp (not something widely used today). I was thinking that Light Emitting Diodes (LEDs) might be a more modern alternative.

    If I ever get around to making one I would use it for relative differences. For example seeing if the emulsion was now sensitised to green light. Exposing some panchromatic emulsion such as Plus-x etc would give a "reference" spectrograph. This avoids the need to calibrate.

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    Yes, you need to know where UV, visible and IR are positioned and the actual wavelengths. Look at some published spectra in Mees and James or here, that I have posted to see how they look. That is about the best I can say.

    Mine is calibrated, and has 2 settings. One is visible and one is IR. If I don't use a UV filter, I get a UV harmonic at 700 nm. This harmonic vanishes with a UV filter and is one of the faults of these particular instruments.

    PE

  10. #10

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    There exist three other forms:

    1.sometimes you can find the Lagorio-tableau – 16 colorstripes are combined with 13-part grayscales. The tableau is around 24x30cm and was made in ?Czecheslowakia?Poland?. Named VUZORT. The U has a accent. I have heard, that other forms had exist.

    2.The Schott variable Interferenzfilter from around 360 to 800nm. It is ca 27 mm x 190 mm, my is combined with a parallel graystep made by grainless bw film. Ideal for 35mm films to control.

    3.In older times scientist had have a pocket-spectrometer. This is today in the program of scientific tools, but you will find often on auctions for history of technology and science. A Zeiss Jena with scale 400-700nm is combined with a simple only mechanical construction from ICA, Dresden (famous camera-company) for 6.5 x 9 cm plates, where a 8mm slit will exposed in 7 following positions. In the plate-cassettes it is simple to mount 2 parallel 35mm stripes.

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