Zoom setting with an umbrella

Discussion in 'General flash photography, lighting, and technique' started by DigitalHeMan, Jun 19, 2011.

  1. I am playing around with my SB-900 and a shoot through umbrella. The results I am getting seem pretty nice with the flash set to 1/8th manual output, triggering with the SU-800.

    I am wondering what zoom setting people would use here? I have it set to 35mm and it seems to be filling the umbrella up nice and evenly with light. The umbrella is around 48" diameter I think....

    TIA
     
  2. fabulas

    fabulas

    321
    Jan 24, 2009
    Memphis, TN
    I set mine to the widest zoom.
     
  3. WayneF

    WayneF

    Apr 3, 2006
    Texas
    I set my speedlight to 24mm zoom for a reflected umbrella, at full shaft length, to fill all of it. 35 mm is probably fine for a shoot-though. It is less critical then, since the outer edges never reach the subject anyway.
     
  4. Thanks Wayne, it's good to have reassurance :)
     
  5. Rob_H

    Rob_H

    511
    Apr 10, 2009
    I normally have them zoomed quite wide, however when setting up the lights I always test fire them and look to see if all the umbrella is filled with light and that now is spilling out to the sides and adjust as needed.
     
  6. WayneF

    WayneF

    Apr 3, 2006
    Texas
    Some notions...

    This is a SB-800 at full power, in a 45" Smith Victor reflected umbrella. It is located very close, with the back of the fabric right up against the background. The flash is mounted at the full maximum length of the umbrella shaft. 24-70mm lens at 56mm. The field of view seen is nearly 6 feet wide. The point is, the shadow of the fabric shows on the background. Light outside the shadow is spill (light inside the shadow is lens flare).

    dse_6650.
    85 mm zoom f/5.6
    Is this objectionable spill? Spec chart says 85mm zoom field is 31x23 degrees.


    dse_6651.
    50 mm zoom f/5.6
    50 mm zoom field is 46x34 degrees


    dse_6652.
    24 mm zoom, f/5.6
    24mm zoom field is 78x60 degrees
    Place the square corner of a sheet of paper at the flash head, sight down its two sides, and see if you think the umbrella could be less than 90 degrees wide?

    dse_6653.
    Wide angle adapter down, 17mm zoom, f/5.6
    Field says 110x100 degrees.


    But when photographing the flash itself, our test exposure always makes about as much difference as anything, which makes it hard to tell exactly what we are measuring.

    dse_6654.
    24mm zoom, f/5.6 (repeated)


    dse_6655.
    24mm zoom, f/8


    dse_6656.
    24mm zoom, f/11


    dse_6657.
    24mm zoom, f/16

    There is the slightest side spill (really, at any long zoom too, merely because the flash head width is 2 inches, offering a view of part of it around the edge of the umbrella, regardless of zoom), but which should do no harm to a close subject (in the forward direction). We also have the concern of filling the umbrella top to bottom too. My own opinion is that 24 mm zoom will fill the reflected umbrella best, using the maximum shaft length.

    Shoot-through is less concerned with totally filling it, the edges get ignored anyway (as shoot-through, they do not aim towards any close subject).


    EDIT: Added evaluation considerations.

    Background is dark gray (Savage Thunder Gray). Distance measures 40 inches sideways from flash head to closest spill area on background (3.3 feet). Which is very wide, so guide number may not be very applicable, but ...

    Full power 24mm zoom Guide Number is 98 ISO 100, or GN 138 ISO 200 used.
    GN 138 / 3.3 feet = f/42 correct exposure in spill area, so f/5.6 is nearly 5 stops overexposed (to make dark gray appear white). Not really that much, but point is, realize that the results shown are exaggerated.
     
    Last edited by a moderator: Jun 20, 2011
  7. Graystar

    Graystar

    109
    Jun 18, 2011
    NA
    I have a Westcott 43” collapsible umbrella. It’s possible to use it with the shaft collapsed. With the shaft at its full extension, I need to set my SB-600 to 24mm to fill the canopy. With the shaft collapsed I need to pull out the 14mm wide-panel to fill the canopy. Collapsing the shaft is useful, as it allows me to get the umbrella canopy closer to the subject when I need to.
     
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