blow out a white background

Discussion in 'Lighting Equipment' started by glenn_s, Jan 15, 2007.

  1. I read on this forum that I should overexpose a white background by about two
    stops to get the classic white background.

    I tried it and had two problems. First, light reflected off the background
    onto the side of the subject's face, causing it to be overexposed.

    Secondly, the background was not evenly exposed - the light dropped off from
    left to right.

    I'm using an AB400 and an AB800. For the main light, I used an umbrella 45
    degrees to the subject's right. I put the background light just out of the
    field of view to the subject's right and just slightly behind the subject.
    Subject was ~4' from the wall. Background light was reflector only (no
    umbrella) and positioned so that none of the light would directly hit the
    subject.

    Any thoughts about where I should place the background light to achieve even
    overexposure on the background without spilling onto the subject?

    Thanks,
    Glenn
     
  2. You need to illuminate the background as evenly as possible - if you can't illuminate it evenly (difficult with a single light) then you need to overexpose the darkest part of it by around 2 stops, which adds to the problem of bounced light.

    And, because light bounces from the background towards the subject, you need the subject to be as far from the background as possible, so that the relected light loses as much of its power as possible before reaching the subject
     
  3. Two lights, one on either side of the background, at an angle of about 30 degrees, so no light is bouncing directly back into the lens. And subject a bit further from the background should do it.
     
  4. Okay let's try to get you an even background that is a hot white. Tough to do with one
    head, and even tougher if you don't have much space. There are a few ways to do it with
    one head. The first way requires more width and the second requires more height. First
    off light falls off faster the closer that you are to the source, so you need to get the source
    as far away as you can from the white so that it will be more even once it reaches the
    white. Putting an umbrella on your strobe will also help you to spread out your light, but
    will then reqire more power. Take it out on about a 30 - 40 degree angle and meter
    across the span you are trying to make white untill you get it as even as you can and then
    adjust your strobe to give you the desired F-Stop. Probably going to be really hard to do
    with the strobes you have as you will most likley not be able to throw enough light at your
    white. You will then need to flag that light off of your subject so that you don't get any
    spill hitting them. The other way wich requires more height is to put an umbrella on your
    strobe and take it up high so that it rakes your white at about a 30 - 40 degree angle. The
    higher you take it, the more even it get's. Again you will have to place a cutter or flag in
    place to keep the spill off of your subject, unless you like the way it is hitting the hair and
    giving you a little bit of rim light.

    The bounce issue has to do with the distance that your subject is off of the white. You
    can take your meter and measure the amount of bouce by standing at your subjects
    position and pointing it at the white when you fire your strobes, Move untill you like what
    your meter is tellign you. When you say that the bounce is making the side of your
    subjects face blown out it is making me think that you are actually gettign spill from your
    strobe and not from the backgound. The background bounces right back at the lens so
    the top of the shoulders and rim of the ears and hair start to see it before the side of the
    face. So flag your strobe off from the subject and see if that fixes your problem. (I know
    you said it was positiond where none of the light would directly hit the subject, but you
    didn't say that it was blocked off completly from the subject.

    Don't set your sights to high with the limitations you have. Make it look the best you can
    with what you have. Don't get discouraged when you look at photos in mags and see a
    large group of environmentalists in Vanity Fair on hot white or George Clooney in Esquire
    on hot white and think, "Man my stuff looks nothing like that." Large budgets, lots of
    lights, and a huge studio space are a HUGE help. :) Just to give you an idea here is a gear
    list that I usually order when I am doing a basic hot white for sombody ina studi.

    6 Profoto 7a 2400 packs
    6 ProHeads
    6 White Profoto umbrellas
    2 C-Stands
    4 Cardalinis
    4 V-Flats
    2 Pocket Wizard receivers
    4 Phono to phono cords

    That is just for the backgound lights if I am lighting a cyclorama. Post up a sample so we
    can see what is going on.
     
  5. I use 2 strobes, White Lightning 800's, on the background. Assuming a 9ft wide paper background, I put one strobe on each side, just off the paper, and about 2 1/2ft from the background. They're angled so each strobe just lights the opposite edge of the BG. I use barndoors to keep light from spilling on the subject. The subject is about 2ft in front of the BG lights. BG lights are at full power, lighting on the subject is 1/2 power or less. I've had no problem with reflections onto the subject doing this.
     
  6. Thank you all for the quick and detailed responses. I'll try the umbrella on the background and moving the subject further out. This is one of the pictures where the side of the face is over-exposed. (He would only pose if I let him hold the drill). Thanks, Glenn
    00JXCc-34444184.jpg
     
  7. You don't need two stops - the key is to evenly light the background. This is very difficult with less than two lights on it, however.

    I wrote a blog post about one way to light a white background here:

    http://www.gregrphoto.com/blog/2007/01/shooting-with-white-background.html

    Also, the brighter your background lights with respect to the subject, the more spill you're going to get on the edges of your subject. One thing you can do is move your subject further away from the background - 4' is pretty close. Do you have room to double that?

    Greg
     
  8. That light on the face is spill from your background strobe and is overexposed because it is combining with your key. Flag the background light off of your subject. Basically all you have to do is put something in the way of the strobe between the subject and the strobe. Make sure that is you stand at the background you can see the strobe, but if you are standing where the subject is you want to make sure you can't see ANY of that strobe. Let me look thru my on-set roids and see if I have an example for you.
     
  9. 2 stops is 1.3 stops too many ... you'll have bleed coming around edges and through hair.
    One photographer blog says to measure the light bouncing off the back of the wall at the position of the model. If it is 1/3 stop over aperture, it is enough.
     
  10. Interestingly i was watching a video by Robert Seale today and about half way through it he explains exactly how to expose for a white background without spilling over to the main subject and creating fringing problems (he claims btw that overexposing the background by 0.7 f stop with digital is sufficient compared to the 1 or 2 f stop with film). Here is the link to the video. Well worth watching.
    http://blog.photoshelter.com/2010/04/lighting-it-up-in-austin-with-robert-seale-1.html
     
  11. J'ai impression qu'on se connait Michel?
    Here are my comments that I posted on another forum regarding that video.
    ----- 2010.04.09 on Dyxum
    I watched it and while I appreciated it I really feel that such presentations lack essential information for people learning to light.
    I "got it", but someone new to studio lighting would be left with more questions than answers.

    I've looked at several such videos (always on the look for good ideas to steal - and I do learn the odd tidbit) but they all lack a good structure. The main failing here, I think, is that great photogs are not necessarily great teacher/presenters.

    Strong points
    -mixed lighting considerations (ambient + flash or flash + flash and exposing bg and subject differently giving more creative latitude)
    -location choice
    -use of scrim, light "focusing", beauty dish, softbox. (Not elaborated enough - see 'goof' below.)
    -he endorsed the idea that he was "over equipped" for the shoot and could have achieved the same with less - even a few speedlights.
    -admitted that some shoots (inc. this one) were "structure on the fly/decision on the fly/exposure on the fly" and not always planned to the t.

    Weak points
    -Far too long a video (could have taken 20-30 minutes for the content given - or could have been as long with more useful content).
    -Poor graphic presentation (detail was not visible, or hardly so)
    -equipment lists were not in sync with the shots
    -Too "static" a presentation
    -Did not show metering actively - this is something beginners need more of (I think. I really learned the essential truths of metering for studio when a pro came to do some corporate shots at work. In 3 minutes I learned more about metering than in any other form).

    Goofs:
    -Using a sock over a grid (though he admits to this folly at the end).
    -a "caller" asked what "specular" meant. His explanation was wrong. Way.
     
  12. Hi Alan je ne sais pas si on se connait, mais votre nom m'est familier.
    I did not post this link because i thought it was a brilliant educational video, i don't think it is, but it did address the question of the OP about mid way through, and being an avid enthusiast, i like watching anything about photography. I always find something new and interesting every time.
     

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