Changes in exposure time using Ilford MG system with LPL colour head

Discussion in 'Enlarging' started by jeztastic, Jan 12, 2014.

  1. jeztastic

    jeztastic Member

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    Hi,

    I'm using an LPL 7700 Pro colour head, and dialing in the multigrade settings. When I went from grade 3 to 3.5 today I had to add about a half stop to the exposure time. Is that usual? Ilford's info states that using the yellow and magenta channels should reduce this problem. They also state exposure times should remain constant till grade 4. I am wondering whether the developer had started to expire or something, but I don't think it was that.

    I was using MG IV RC paper and Ilford MG developer.

    Thanks!

    Jez
     
  2. pentaxuser

    pentaxuser Subscriber

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    This hasn't been my experience. I am assuming you are using the Ilford multigrade dual filtration settings and if so the difference between grade 3 and grade 3.5 is very little. Have a look at Ralph Lambrecht's Darkroom Magic website where he lists the changes necessary when changing grades. From grade 3 to grade 3.5 the increase in exposure is 1.12 - nowhere near the 1.5 which is half a stop extra exposure.

    I also think you may be confused between colour head dual filtration and Ilford multigrade filters. With these the exposure stays the same for grades 00 to 3.5 then doubles for grades 4-5.

    I use a Durst enlarger but I don't think this matters. The increase in exposure that R Lambrecht's has worked out applies as far as I know to all enlargers using dual filtration settings. I take it that you are using the dual settings that Ilford recommends for LPL enlargers. Ilford has given settings for different groups of enlargers. You need to be sure that you are using the correct settings for the LPL group

    If the developer is fresh and your colour head filters are working properly then I am puzzled about needing an extra half stop.

    pentaxuser
     
  3. MattKing

    MattKing Subscriber

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    All of the "speed matching" systems suffer from one important limitation - the sensitivity is matched for only a single tone. So the results you obtain will depend heavily on whether the predominant or most important tone in the scene is the same as the tone that is speed matched.

    The Ilford filters seem to be speed matched on a mid-gray tone. IIRC, Ralph Lambrecht's suggestions are speed matched on more of a highlight tone.

    In any case, the speed matching will get you part way, but additional test prints will most likely be needed.
     
  4. horacekenneth

    horacekenneth Member

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    I've experienced the same thing. Seems like every step up after 2 or 3 needs a little more exposure. I am using Kodak MG filters.
     
  5. Rick A

    Rick A Subscriber

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    According to Ilford, there should be no difference until after grade 3, then you need to add at least one stop more between 3 and 4 and another between 4 and 5. The half stop more exposure added is right on target with this.
     
  6. Ronald Moravec

    Ronald Moravec Member

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    Ah men. They are matched for middle grey. I usually print for matching whites and increases are necessary.
     
  7. ic-racer

    ic-racer Member

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    Are you are using the "Kodak" table in the Ilford literature that goes from (162Y/0M) to (0Y/150M)?
     
  8. Bob Carnie

    Bob Carnie Subscriber

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    the big jump is when you hit G4

     
  9. jeztastic

    jeztastic Member

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    Ah, this is useful information. This may have been the problem.