How much light fade-off of enlarger is reasonable.

Discussion in 'Darkroom Developing and Printing' started by Steven Woody, Jan 9, 2007.

  1. Steven Woody

    Steven Woody Guest

    i am not sure whether my fade-off is really a fade-off. the enlarger
    is an Omega D5XL, it's a color header enlarger which got a soften-box (
    light multipler ) soften the light from bulb before pass them to lens.
    yesterday, i projected and focused a 8x8 inch image on the baseboard
    from a 6x6 negative, after removing the negative i tried to meter the
    light strength on the baseboard. i used a Sekonic 508 meter ( yes,
    it's not a enlarger meter, but i'd not get one ), to meter it's
    center/corners and found the corners get some fade-off, which is about
    0.2ev-0.5ev less than the center.

    is it normal?

    -
    thanks.
     
    Steven Woody, Jan 9, 2007
    #1
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  2. Aside from your rather bizarre speech to typing syndrome-yes it is.

    Falling off for now.
    Best regards.
     
    Little Green Eyed Dragon, Jan 9, 2007
    #2
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  3. Steven Woody

    dan.c.quinn Guest

    The 2 1/4 square carrier in a 4x5 enlarger? Down 0.2 to 0.5
    EV center to corners. That is very bad, intolerable. Something
    is wrong some where. Bad even with 4x5 center to corner. Dan
     
    dan.c.quinn, Jan 9, 2007
    #3
  4. Steven Woody

    Steven Woody Guest

    sorry, i am not a native speake :) the below reply said it is bad but
    you said it is normal. which one is right?
     
    Steven Woody, Jan 9, 2007
    #4
  5. Steven Woody a écrit :
    Sensors are very sensible to the angle of the light that reaches them.
    With a wide angle, the same light intensity will appear much lower than
    it really is.
    So, if you did the measure while keeping the cell flat on the enlarger
    base, most of the difference could just come from this measure error.
    When measuring in the corners of the image, you have to turn the cell
    so it remains perpendicular to the light.

    Sensitive emulsions, like films and papers, are much less prone to this
    phenomenon and thus will not show so much difference.
    To put in evidence how much your enlarger is really affected by the
    light fall-off, then, just use plain paper, no negative in the carrier
    and adapt exposure to obtain a mid-grey.
    A hard paper grade will show the effect the most, the softer the less.

    Claudio Bonavolta
    http://www.bonavolta.ch
     
    Claudio Bonavolta, Jan 9, 2007
    #5
  6. Steven Woody

    John Guest

    And if you get really picky (who me ? !) take the print, hopefully a
    nice medium gray, to a lab and have them run a densitometer over it.
    Should take them about 30 seconds to map the corners and middle.

    You might also consider trying a different aperture. Some lenses cause
    more falloff than others.

    ==
    John S. Douglas
    Photographer & Webmaster
    Legacy-photo.com - Xs750.net
     
    John, Jan 9, 2007
    #6
  7. Steven Woody

    John Guest

    It is and it's common and it's bad.

    ==
    John S. Douglas
    Photographer & Webmaster
    Legacy-photo.com - Xs750.net
     
    John, Jan 9, 2007
    #7
  8. It's not great, it's not terrible.

    FWIW: the intensity map of a Beseler 45 condenser, 150 Rodagon,
    f11, 4x5 carrier:

    8.97 9.08 8.98

    9.12 9.43 9.15

    9.04 9.22 9.04

    Numbers are DA EV's - in stops. Again, outstandingly
    mediocre.

    When you measure be sure to close down the lens - wide
    open any lens's fall off is bad.

    I know this guy, he can get them for you wholesale,
    straight from the factory.
    Depends on the sensor. Spotmeters tend read low
    off-axis... Spherical integrators don't have fall
    off, or sure aren't supposed to have fall-off.
    It depends what you are measuring. If it is light
    from a bulb then the sensor, if angle sensitive, should
    point to the source.

    If you are measuring the light as it will affect the
    paper the sensor needs to be in the same plane as the
    paper. So a flat detector laying just where the paper
    will be is the correct measuring instrument.

    There is often a slight light direction sensitivity,
    this is lessened if you measure with the sensor oriented
    radially. For most purposes it doesn't matter.
    The best and cheapest test: if it looks OK, it's OK.
     
    Nicholas O. Lindan, Jan 9, 2007
    #8
  9. Steven Woody

    Steven Woody Guest

    thanks for your answer and advice. i will redo the test in this
    weekend according what you adviced and report the result back here.

    -
    woody
     
    Steven Woody, Jan 10, 2007
    #9
  10. Steven Woody

    JJ Guest

    That's not the way to measure the outcome. Make a print with a clear
    negative with a mark in the center upon which to focus, with the lens
    wide open. Then at your typical stop (two down). Then judge.
     
    JJ, Jan 12, 2007
    #10
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