Determine required flash power

Discussion in '35mm Cameras' started by Justin F. Knotzke, Feb 7, 2005.

  1. Hi,

    I am looking to purchase studio lights, mostly likely Alien Bees. How does
    one go about figuring out what kind of power they need? 9/10 I will be
    shooting a small group (say under 5 people) but there will the the occasion
    where I will shoot 30 or so.

    Would one strobe cover this situation or would I need two?

    How do you determine how much flash power you need before actually arriving
    at the location?


    Justin F. Knotzke, Feb 7, 2005
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  2. Justin F. Knotzke

    Matt Clara Guest

    Two B800's. Get the sturdy stands, too. I use mine for everything from
    weddings to much smaller studio setting portraits.
    Matt Clara, Feb 8, 2005
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  3. Ok. That's what I will probably do. Thanks for the tip.

    Justin F. Knotzke, Feb 8, 2005
  4. Justin F. Knotzke

    Matt Clara Guest

    The biggest group I've done is about 20-25, but there was more than enough
    power for that.
    Matt Clara, Feb 8, 2005
  5. Justin F. Knotzke

    Alan Browne Guest

    You should have at least two lights. 3 - 5 would be better.

    Google on this NG and you should find a recend discussion on this.

    An Alien Bee 400 and 800 would (160 & 320 W-s) cover it nicely.
    There is no 'formula' that helps directly for a variety of reasons including
    umbrellas/reflectors, efficiencies, etc.

    So: Overkill, at least some.

    Consider softboxes/umbrellas, film speed, etc.

    I would say that a set of bees (400+800) will cover the first situation even
    with umbrellas @ ISO 100 and you'll get f/5.6 to f/8 or so. But you won't have
    much left over power if you need some smaller aperture shots. Ideally, with one
    fill light further back it should be more powerful than the key light which is
    usually closer in. (even though the fill may be set at 1 to 2 stops down from
    aperture setting, it will be further back so more power is needed).

    For 30 people or so the problem is that you have to light from further back (for
    even illumination) and Mr. 1/r^2 comes into play. More power certainly. But
    with a group you are likely to use a more even lighting than with a small group
    or for a portrait. So place the lights back on each side of the camera (ahead
    or behind) and use each to light the whole group. A couple 800's would be okay.
    (With a group, because of depth you'll want to shoot at f/11 if you can).

    You can also get a cheap little AC strobe (40 W-s) to light the background
    partially behind the subject or to throw hair/rimlights.

    Bees can't be bought at the store. You have to order. That will add to the
    price somewhat. You'll need a flash meter too.

    Alan Browne, Feb 8, 2005
  6. Justin F. Knotzke

    Matt Clara Guest

    Alien Bees recommends against mixing and matching alien bee units of
    differing power output. Really not a problem if you don't mind your
    modelling lamps not representing accurately the ratios of output between the
    lamps of differing power.
    Matt Clara, Feb 8, 2005
  7. Right. And thanks for the tips. Much appreciated. I've been looking at the
    light offerings here in town and they seem all very expensive compared to
    Bees. I just have to decide if one light is enough and rent the other or buy
    the second..

    I think I'll start with one and the 1 or 2 times a year I need two, I'll

    But ideally I just want to learn how to use artificial light as much as

    I'm also going to need portable power. I suppose those vagbond battery
    packs are good enough?

    Justin F. Knotzke, Feb 8, 2005
  8. Justin F. Knotzke

    Alan Browne Guest

    The reason they say that is that both the 400's and 800's use 100 W modeling
    lamps. Wattage (by number) has little relationship to the amount light coming
    out so simply replacing the 400's 100W lamp with a 50 W lamp won't help either.
    (He could try finding a lamp with half the lumens, OTOH the Alienbees lamp
    control is probably set up for a 100W bulb).

    OTOH modeling lamps are so notoriously unrepresentative of the actual flash
    power that I doubt it's of any real consequence. Esp. if one light is used as a
    fill light and the other as key, then I doubt that 'matched' or differing lights
    will really show much difference. And since film doesn't record light the way
    our eyes see it, modeling lights are further guidance, not representative.

    Use the modeling lights to get a feel for what the light will look at, use the
    meter to get the ratio right.

    In the end, Justin would be better served with two 800's than a 400 + 800 if he
    wants to spend the extra sheckles.

    Alan Browne, Feb 8, 2005
  9. Justin F. Knotzke

    Alan Browne Guest

    Justin F. Knotzke wrote:

    I believe that requires two strobes for best effect. At least one for fill, one
    for key. A third cheap AC strobe (CAD$60) for the BG/rim.

    Note, if you use fast enough film+aperture, an AC strobe -might- be adequate for
    No idea. I suppose if you dig (or write) the Alienbees site will give you some
    idea of how long the batts last in "shots". I've shopped for inverters but the
    cheap ones are not sine wave. Most strobes manuals state that sine wave
    inverters are required.

    How did the ringlight work out?

    Alan Browne, Feb 8, 2005
  10. Justin F. Knotzke

    Matt Clara Guest

    Hey Justin, if you're going to start with one light, you might want to see
    if you can stretch the budget for the really big softbox to go with it.
    Matt Clara, Feb 8, 2005
  11. Justin F. Knotzke

    Paul Bielec Guest

    As Alan already said, you'll need 3 lights for portrait in order to get
    good results.
    With just one spot, you have to place it at an angle to get some relief.
    You end up then with the other cheek too dark and you need another spot
    from the other side. Then you need a 3rd one from the back for the hair.
    Keep in mind that studio portrait is all about the light. Getting the
    exposure right is fairly easy compared to setting up the lighting.
    Paul Bielec, Feb 8, 2005
  12. Check. I might get two lights in the end. I hate not having a complete
    setup because of money. I rather go with nothing instead.

    Justin F. Knotzke, Feb 8, 2005
  13. Mostly just playing around. I'm not entirely crazy about the manual
    options. The TTL auto seems nice and acurate but the manual mode leaves much
    to be desired. I am going to get a flash meter shortly.

    But I managed to get media acreditation to the Canadian Ski Marathon and
    the Coureurs de Bois start at 05:30. I am going to take lots of in close
    portraits of the guys and girls at the start using the ring flash. Then
    hopefully get them at the finish as well for a combo before/after shot.

    That's this weekend..

    Justin F. Knotzke, Feb 8, 2005
  14. Justin F. Knotzke

    Alan Browne Guest

    I look forward to the posts... if you're using a monopod and there is some
    ambient spotlighting, try dragging the shutter at about 1/10 - 1/20 in rear-sync
    on some of the shots.

    Alan Browne, Feb 8, 2005
  15. For 5 to 15 people (1 to 2 rows), one into an umbrella or 3x4' light box
    boomed over or right next to the camera will do. For 25 or more (2 to
    3 rows), you'll need two.
    I just bring everything. 4 - 1000WS power packs and 9 heads +
    accessories. Okay, a more reasonable answer. I have a little battery
    powered location lighting kit I put together from "parts" that fit your
    criteria: 3 - Vivitar 285 units each with a Quantum battery, a couple
    small umbrellas, a couple of small light boxes, 3 stands, lightweight
    boom, reflectors, etc. The lights, batteries, cables, etc. fit in an
    old F2 Domke bag. Everything else goes into a tripod bag, along with
    the tripod. Perfect for 35mm and useable for medium format. With 100
    speed film, you should get f-stops between f4 and 8, depending on the
    setup. IIRC, the 285s are rated at about 60WS with 100 speed GN of
    Stefan Patric, Feb 9, 2005
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