Preflash multigrade paper

Discussion in 'Enlarging' started by henk@apug, Nov 23, 2010.

  1. henk@apug

    henk@apug Member

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    "Pre-flash can be used at different contrast filtrations depending on the effect required"

    I read this in a book but unfortunately, the "effect required" was not specified.

    So my question is what are the effects of pre-flash at different grades ?

    Thanks !
     
  2. makanakijones

    makanakijones Member

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    I have never heard about this.
    Do you mean to put a filter at the light source and flash?
    This could have a point. Using a 00 filter you could get tone at lights easily.
     
  3. henk@apug

    henk@apug Member

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    What I ment is when using an enlarger for preflash, one can preflash the paper
    at different filter grades.

    I was wonedering what the different effects are of preflashing with grade 0 or 2 or 4or...

    I think I will spend a day in the darkroom to find out :smile:
     
  4. RH Designs

    RH Designs Advertiser Advertiser

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    White light is best for flashing. Flashing through hard filters just increases overall exposure, flashing through soft is much the same as white light. So spend your day making pictures instead of experimenting :smile:.
     
  5. ic-racer

    ic-racer Member

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    Sure, flashing multigrade paper works. I suspect if you lost your "00" filter, or if you want to treat only a portion of the image you might want to do it. But otherwise, its not needed.
     
  6. henk@apug

    henk@apug Member

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    Good advice RH !

    By the way, i really enjoy using your f-stop timer :smile:
     
  7. Ian Grant

    Ian Grant Subscriber

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    Flashing is used to help bring out the detail in the highlights and is often used in combination with a higher paper grade / filtration setting so flashing using a contrast filter is of no benefit ans it'll need to be excessive to make an impact on the highlights.

    Most people do the flashing separately to the exposure often using a second enlarger. Split grade printing would be more beneficial tahn trying to do teh flashing through filtration.

    Ian
     
  8. michael_r

    michael_r Subscriber

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    With VC paper, I think white light or ~grade 2 filter would give pretty much the same effect for the pre-flash exposure. I might consider deviating from that if my main image-forming exposure was going to be done with a very soft or very hard filter though. My reasoning there is, if for example the print was mostly going to be exposed at grade 5, the high contrast (blue sensitive) portion of the emulsion is forming most of the image, so assuming the pre-flash is intended to bring the paper to threshold exposure, I'd be trying to "activate" the blue-sensitive layer with the pre-flash.
     
  9. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    In general, flash with the same filter you use for printing.

    Flashing with white light will work as well as anything for medium to low contrast filtration but has no advantage.

    For high contrast filtration you really do need to flash with the printing filter. At the high contrast filtrations the curves of the individual emulsions are moved so they stack directly over eachother. Flashing a high contrast print with white light or a low contrast filter will effect only the green sensitive emulsion - one of the three that add up to make the final image - and the results will be week. If the white light flash exposure is increased in an attempt to get a visual movement in the highlights the result will be overall fog in the green sensitive emulsion.

    If you always flash with the same filtration there will be no problems and no worries.

    It should be noted that all emulsions in VC paper have the same intrinsic contrast.

    See http://www.darkroomautomation.com/support/appnotevcworkings.pdf
     
    Last edited by a moderator: Nov 25, 2010
  10. jerry lebens

    jerry lebens Member

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    I used to use two enlargers until it was pointed out that I could achieve the same result just by putting a scrap of diffusion filter gel (usually Rosco Tough White) over the lens to scramble the light.

    Regards
    Jerry
     
  11. bsdunek

    bsdunek Subscriber

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  12. Ian Grant

    Ian Grant Subscriber

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    With my Durst I could just use the diffuser filter used for my clour analyser, good thinking :D

    In practice it's the time it would take to change timer settings and variations with filtration, columns height, neg density that make using the second enlarger system quicker. I know my basic flashing exposures with the Durst set to f16 at the top of the column, and they remain constant regardless. I mainly use a De Vere 5108 and I'd rather not be flashing it's 2000W's of bulbs :smile:

    Ian
     
  13. pentaxuser

    pentaxuser Subscriber

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    I am presuming that the diffuser filter is used to avoid removal of the negative from which you wish to flash the print. Given that the flashing exposure has to be quite precise and be the same each time, can you be sure that the correct flash exposure with the diffuser and the particular neg would be replicated with another neg.

    In other words provided the enlarger is set at the appropriate height,aperture and correct exposure for flashing does a diffuser ensure that this is repeated each time irrespective of whether a negative is contrasty or "thin"

    I'd be concerned that a different neg might result in a different exposure under the diffuser or is this not the case? I had always assumed that this is the advantage of the RH Designs flasher lamp which ensures that the correct flash exposure is repeated each time by having it at the same height over the easel and set for the right exposure after testing for the correct flash exposure.

    pentaxuser

    pentaxuser
     
  14. jerry lebens

    jerry lebens Member

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    I treat each negative individually and make a fresh pre-flash test for each one, ie. I don't assume that the same pre-flash settings are appropriate for all negatives. The diffuser allows for this and, as you say, it can be done on the spot without removing the neg (btw, I've never had problems with coverage)

    I can see the attraction of a consistent exposure, but it wouldn't necessarily fit in with my preferred work flow, which requires greater flexibility.

    Different strokes, as they say...

    Regards
    Jerry
     
  15. henk@apug

    henk@apug Member

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    Thanks for clearing things out.
    Flashing at the same grade the print is made makes a lot of sence in fact. With
    fixed grade papers this is also exactly what happens.

    For me there is only one drawback to use a second enlarger. If preflashing with a time higher than the optimum, white borders would become "contaminated", so the paper has to be flashed in the easel at both enlargers, so recomposing is necessary after flash