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  1. #1

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    Filter transmission curves

    Thought some of you might find this interesting. I was playing around with the new spectrometer in the lab and my 25, 47, and 58 Tiffen filters happened to get delivered today. So I made transmission curves for them. Note the source light was just a crummy flashlight which is pretty light on the blue end of the spectrum, so the curves are a bit skewed (there's only so much the software can compensate for). I did a quick test using window light and the transmission hump in the blue end of the spectrum for the 47 filter was about 30%, compared to the 20% from the flashlight.

    The other graphic is the actual output of the spectrometer for each of the three filters and the source flashlight.

    Notice the HUGE amount of IR that all three of the filters lets through.
    Attached Thumbnails Attached Thumbnails transmission.jpg   light.jpg  

  2. #2
    Sirius Glass's Avatar
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    That is interesting. Can you repeat these test with sunlight? Additional filters?

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  3. #3

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    Sunlight, maybe, maybe not. I'll have to think about how to get a decent amount of sunlight into the spectrometer. But I should be able to rig up a better light source than a flash light. We'll see.

    Can't do much more in the way of filters since I don't own that many more. A couple UV filters, an R72, and a B+W dark red one...

  4. #4
    Lee L's Avatar
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    Many standard filter curves from Wratten and B+W filters that I've seen also show the high transmission in IR. Most films drop off in sensitivity very quickly after 650nm or so, which makes the filters effective within the spectrum of the film. I suspect it would also be much more expensive to produce filters that block IR (unnecessarily in the case of most films) in addition to the visible spectrum.

    Lee
    Last edited by Lee L; 02-05-2009 at 06:24 PM. Click to view previous post history.

  5. #5

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    Interesting variation in amplitude for each of the filters. I would have expected them to be a bit closer. Of course, the source contributes to the variability of the curves.

    I would be very interested in the UV filter response and matching that response to respective manufacturers. I know some are quite good at blocking UV and some are awful!

    Thanks for the information!

    -Fred

  6. #6

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    As far as the variability of the source, the transmissions should be calculated relative to the source, negating any contribution of non-uniformity in the source. However, you can see in the blue there is not much signal, and the SNR starts to get a bit bad there.

    Any body have standard filter factors for 47 and 58 filters? I'll play around tonight with my light meter to calculate them, but they should point to the differences in overall magnitude amongst the filters.

  7. #7
    ic-racer's Avatar
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    If you have a spectrometer, the kind of thing I'd like to see is processed B&W film transmission spectra. Like we have all seen that certain films are more blue or pink after processing. Interesting to see the magnitude of that film base tint. Also, how about stained negatives...would be interesting to see how the spectra differs for different types of staining developer.

  8. #8
    Photo Engineer's Avatar
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    Quote Originally Posted by ic-racer View Post
    If you have a spectrometer, the kind of thing I'd like to see is processed B&W film transmission spectra. Like we have all seen that certain films are more blue or pink after processing. Interesting to see the magnitude of that film base tint. Also, how about stained negatives...would be interesting to see how the spectra differs for different types of staining developer.
    Easliy done.

    Here are the spectral sensitivities of Ortho, Pan and IR films.

    PE
    Attached Thumbnails Attached Thumbnails dye types.jpg  

  9. #9

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    As in just hold a piece of fixed (or unfixed) film and see it's transmission properties? I can do that for sure.

    I also have access to two UV spectrometers, but I think they are probably less useful...

  10. #10
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    Ron, I don't think ic-racer means the spectral sensitivity. I think the question is motivated by concern about the UV transmission of the film stain and base, which is especially important for alt printing.
    "Only dead fish follow the stream"

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