Ilford Contrast Filter Spectra

Discussion in 'Black and White' started by scottk, Jun 6, 2020.

  1. Hello- I am looking for the transmission spectra for the Ilford Multigrade Contrast filters. I've been through the web, no result. Even contacted Ilford but no reply after 2 months. Thanks.
    cameragary likes this.
  2. The Ilford multigrage paper data sheet, on line, gives equivalent values in terms of Magenta and Yellow filter settings for various color enlargers. The magenta and yellow filters referenced are the values of Kodak's CP (color printing) and CC (color correcting) filters. The CC filter set is made using gelatin filters, the CP filters are identical, only the material is acetate. Why not tell us your application and perhaps we can advise you as to how to proceed.
    cameragary and William Michael like this.
  3. William Michael

    William Michael Moderator Staff Member

  4. It's possible that Ilford has those filters manufactured to meet their needs by an outside source. If so, that manufacturer might have the transmission spectra. Finding out the name of the manufacturer might be difficult. As a couple of members have suggested, knowing what application these filters are needed for would help us to advise better. From my use of Kodak Polycontrast filters I would imagine the Ilford filters are similar since both brands work well with multigrade paper. The Kodak filters cover a broad range rather than a narrow band of wavelengths like astronomy filters.
  5. Hi, it's pretty unlikely that a company's vendor is gonna release such specs without explicit permission. In which case you would expect that Ilford, themselves, would be the ones to present the info.

    I would think that obtaining the information from Ilford is mostly a matter of finding the right ear and explaining a purpose for such info. Unless the information is difficult to dig out (perhaps it is buried in vendor contracts that only certain people can get at) I don't see any obvious reason why it needs to be kept secret.

    If I personally wanted the info, and Ilford was not forthcoming, I'd consider just having a local testing lab run them through a spectrophotometer. Might cost a couple hundred dollars, as a wild guess, and might require clipping off a small piece of the filter. Or if one has a friend with an i1 unit (not the "display" version) they could probably get the basic readings (you have to also read the light source).
  6. Thanks Alan, I've looked at a few of the Iford paper tech sheets but don't see what you are referring to. Could you post an example link for me to look at? There are a lot of things on those tech sheets I don't understand (yet). If there are equivalent CC filters I could probably find their spectral info online as B/W filter info is available. My purpose is personal education/understanding to see how things work. I'd like to plot the transmission spectrum of each filter against the emission spectrum of the enlarger light source. Adding to that, the spectral sensitivity of papers.
  7. Ilford used to have a fact sheet called "Contrast Control;" this has the equivalent yellow/magenta filtration.

    For filter data the Kodak Wratten filter data is published in Kodak publication B-3, named, I think, "Kodak Filter Handbook." I think the spectral data is also in the CRC Handbook of Chemistry and Physics.
  8. Thanks Bill, this is great information. I'll have to wait until the campus library opens for the CRC handbook, but, in the meantime, Iford Contrast Control is <$10 on ebay. Thanks.
  9. Wait, wait... should be free download from Ilford website...
  10. [​IMG] upload_2020-6-8_8-31-47.png
    The CC (color compensating) filters. The values omit the decimal point. Thus 50Y = 10^0.50 density to blue light.
    Last edited: Jun 8, 2020
  11. SORRY! My mistake. I ment kodak Filter Handbook was <$10. Alan kindly gave me the link to the Contrast Control tech sheet.
  12. These diagrams are GREAT! I actually print with a Saunders Color head. When I dial in 30M does it correspond to the curve here?
  13. When I go back to work next month(on furlough now) I'm happy to run my 14-filter set a spectrophotometer. It's a few minutes of work-I just don't have access now.
  14. @scottk --- 30m is an abbreviation for 0.30 magenta. This is log notation base 10. Often written as 10^0.30 (10 elevated to the 0.30 power). When converted to ordinary numbers 10^0.3 = 2. The value 2 is the filter factor for this filter. A magenta filer is a green blocker. The 2 tells us that it absorbs 2X of the green light. Since a magenta filter does not significantly block red or blue, we can say a 30 M stops 1 f-stop worth of the green light while not significantly blocking red or blue energy. Another way to view this -- A lamp outputs 100 units of red, 100 units of blue, and 100 units of green light. Impose a 30M and the output will be 98 units of red, 98 units of blue and 50 units of green. The secret is a knowledge of log base 10 math. Log values have traditionally been used in photo math. We measure exposure and film and paper blackening in log units because we make graphs. The graphs, if made using ordinary numbers are too big an thus cumbersome. Log values make the graph manageable as to size and some say the graph is elegant. Anyway, this is the practice used since the turn of the 20th century, about 1890.
    Last edited: Jun 9, 2020
    scottk likes this.
  15. That would be fantastic! Looking forward to the results. Thanks!!
  16. I'm wondering whether part of the contrast control mechanism is to modify the Callier co-efficient of the film? I believe that blue light is scattered more strongly by the silver image particles. Therefore if you reduce the blue-violet component, the Callier effect will be weakened and the contrast softened. Or maybe not!

    I know this isn't the way that multigrade emulsions are supposed to work, but it could be a contributing factor. Modifying the Callier co-efficient would thereby alter the grades got between enlargers with different degrees of diffusion. And give noticeably different results with chromogenic B&W film.

    FWIW, the CC filter density is given as the maximum density to light of the filter's complementary colour - roughly. This will vary between efficient dichroic filters and 'rough & ready' dye filters. Dye filters are also prone to fading. So IMO, looking too closely at transmission characteristics is slightly over-complicating the matter.

    If any 40 Yellow filter presents 0.4 units of density to the maximum blue sensitivity of a multigrade paper, while passing the relevant green, then it'll do the job. Regardless of its red density. Transmission spectra will also be the inverse of density spectra.

    You can also see from the curves that Alan posted, that the density of the 'transparent' filter base (~ O.1D) is discounted from the nominal filter density.
    Last edited: Jun 9, 2020
  17. Not long before I inherited my grandfather's darkroom supplies, including his Varigam filter set,
    he told me that they work just fine on Polycontrast.

    The calibration in terms of contrast grade might be slightly different, especially at the
    far ends. (0 and 5 grade.)

    Having the exact spectra for the filters won't make it easy to calibrate them
    into paper grades, or compare different filter sets.
  18. Kodak CC filters
    Grade 00 = 200Y
    Grade 0 = 90Y
    Grade 1/2 = 70Y
    Grade 1 = 50Y
    Grade 1 1/2 = 30Y
    Grade 2 = none
    Grade 2 1/2 = 5M
    Grade 3 = 25M
    Grade 3 1/2 50M
    Grade 4 = 80M
    Grade 4 1/2 = 140M
    Grade 5 = 200M

    Kodak CP (color printing) and CC (color correcting) are interchangeable and can be stacked.
    CP uses inside the lamphouse CC when imposed in the imaging forming rays as they are optical flats.
    scottk likes this.
  19. The above linked Ilford paper gives settings for four different colour heads.

    However, it also says that there is up to a one grade difference between condenser and
    diffusion enlargers. They don't have.a chart for CC and CP filters, assuming in that case that
    you will just use their filters.

    There is also a difference between cold cathode lamps and tungsten lamps.

    Given all that, you should probably not consider the numbers above too strictly, but as
    good starting points.

    Also, as well as I know, close enough for other VC papers.
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