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  1. #21

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    At 200M, you're already way past what the paper will handle in terms of contrast, unless your filter element has faded or scaled off its coating (sometimes but rarely happens). You can also just place a hard blue filter like a 47 under the lens, if it's of good optical quality, and nothing but the blue light will get thru.

  2. #22
    cliveh's Avatar
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    I would suggest your problem lies with your original exposure of the negative and its development.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  3. #23

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    Thanks to all for the helpful comments. I did not expect this many responses to what I had seen as a simple question. The question was not specific to a particular image but was a general question for a future option. I’m currently pondering the benefits/burdens of unsharp masking and filtration seemed to be a key factor. I was considering a few issues with the replacement of the cyan filter with a magenta one.

    1. Several paper manufacturers’ datasheets show the Omega system (based on Kodak cc units) will not achieve a G5 contrast without additional filtration. Wouldn’t adding magenta into the light path be equivalent to adjusting cc filter packs in the old days of color printing? Of course, the amount added to reach maximum effective magenta light may only be 50 units from the second filter.

    2. The Omega system efficiency is reduced with the small amount of light leakage around the filters. In addition, no filter is 100% effective, so the system never achieves the potential maximum magenta light. I figured that the extra filter is needed to get it closer to the maximum.

    3. As I have measured it, with MGIV I get around G4.25 in Dektol 1:2, which would be sufficient 90% of the time. I know that I can use different dilutions, longer developer times, or specialized developers but I thought the additional magenta filter would be the easiest to incorporate.
    If the unsharp masking technique becomes a routine practice for me, this seemed to be the best long-term solution. Nothing else would change, only the added option to crank-it-up-to-11 when needed.

    I’ve had the head completely apart for a thorough cleaning; so replacing the filter isn’t difficult. The current filters are intact, clean, and the mechanisms work smoothly. With a B&H cost of $68.99 with shipping for a new filter, I don’t plan to move quickly on this project. Maybe I can find a used color head to cannibalize.

  4. #24
    Nicholas Lindan's Avatar
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    The reason you can not get to maximum contrast with a color head is because the magenta of the color head is different than the magenta of a VC filter. Just the same as there is not one color 'green' there is not one color 'magenta'.

    A color head's spectrum is matched to the sensitizing dyes used in color paper, and these are different from sensitizing dyes used in VC paper. The cutoff of color and VC filters is different. For maximum contrast a VC filter can not pass even the slightest hint of greenish-blue light.

    You can add a zillion dichroic filters and it won't affect the maximum contrast because it won't change the filter's cutoff.

    To get more contrast you need to place a real #5 VC filter in the light path.
    DARKROOM AUTOMATION
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  5. #25

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    Quote Originally Posted by MattKing View Post
    It is rare that I would consider disagreeing with Doremus, but ... If the filter is a dichroic filter, it is an interference filter that won't fade. They do, however, become less effective if they become dirty.
    Matt,

    Please continue to disagree with and correct me whenever you see fit! Thanks for the heads up. I have done a bit of research on dichroic filters and the technology behind them and now know that they will not fade since the color of the filter is inherent in the interference characteristics of the coatings.

    If you hadn't posted, I would not have read the articles on dichroism and thin-film interference.

    Thanks,


    Quote Originally Posted by Nicholas Lindan View Post
    The reason you can not get to maximum contrast with a color head is because the magenta of the color head is different than the magenta of a VC filter. ... You can add a zillion dichroic filters and it won't affect the maximum contrast because it won't change the filter's cutoff.

    To get more contrast you need to place a real #5 VC filter in the light path.
    Amen to this.

    Best,


    Doremus


    www.DoremusScudder.com

  6. #26
    Nicholas Lindan's Avatar
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    ... dichroic filters ... will not fade ...
    Well, almost.

    Dichroic filters will pass/block multiples of the pass-band frequency. They are often combined with a regular old dye filter to absorb any unwanted harmonics.

    For photographic applications this is only of academic interest.

    When used for photometery the addition of an absorbance filter is often required: A filter used to analyze a chemical absorbance at 700nm (deep red) would also pass 350nm (deep purple) and so a red dye filter is sandwiched with the dichroic.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

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