Compare Power: HS Flash vs Studio Strobe

Discussion in 'Photography Beginners' Forum' started by clockwurk, Mar 4, 2010.

  1. clockwurk

    clockwurk TPF Noob!

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    I am trying to assemble a lighting kit and I wanted to know if there is a spec that I can compare hot shoe flash power vs typical studio strobe?

    For example, I see that the Alien bee B1600 can deliver 640 true wattseconds + 1600 effective wattseconds, but I do not see similar stats on the Nikon Sb-900.

    Basically, I want to be able to compare how much more power the studio strobe has over hot shoe flashes.

    Hope this makes sense...

    Thanks in advance.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Watt seconds are a good way to compare studio lights, as it's basically the actual light power that the unit fires at. But that doesn't necessarily translate to to photography until you factor in the modifiers. For example, you might have a reflector dish on a studio light, well the light that you get (shape & distance etc) will be largely determined by the size & shape of the dish. Same deal with umbrellas or softboxes etc.

    Flash units, on the other hand, are more often used as-is because they have a built in dish & lens. So they are usually measured/described with their Guide Number (GN), which translates directly to photography. Divide the GN by the distance to the subject and you get the aperture value (f number) for the exposure. (at ISO 100)

    If you look hard enough, you might be able to find a GN for a studio light with specific modifier. For Example, you might find the GN for a B1600 with standard 7" reflector. Note that it's usually given in feet and/or meters.

    I think the rated GN of the SB900 is 34m, but that depends on the zoom setting of the flash head.
     
    Last edited: Mar 4, 2010
  3. Derrel

    Derrel Mr. Rain Cloud

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    A typical high-end strobe like a Canon 580 EX-II or a Nikon SB800 or SB900 has an "approximate" watt-second equivalent to about 80 watt seconds at full power. It's difficult to put a rating on it because of a number of factors.

    With studio strobes, the reflector's angle of coverage plays a *HUGE* part in the exposure it will deliver. The Guide Number in the USA is almost always given at ISO 100, in Feet. In Europe, it is almost always listed in Metres, so the GN will be much lower, since a meter is about 3.1 feet.

    Most studio flash makers will have specifications in Guide Number; Some makers will list their GN for their "standard" reflector, which may be a 5-inch, a 7-inch or an 8- or 8.5- inch inch reflector that covers anywhere from 105 down to as little as 55 degrees. The wider the angle of coverage, the lower the Guide Number is going to be. Some manufacturers will list their GN using an 11 or 11.5 inch reflector, which is usually a rather deep bowl-shaped reflector, often covering between 50 and 65 degrees,and usually delivering a very powerful, well-focused flash output, and usually THE MOST powerful or higher Guide Number output that flash head is capable of giving.

    Paul C. Buff and the Alien Bees just got a new 11 inch long-throw sports reflector, with a narrow beam angle and a highly polished bowl. DynaLite also has a similar flash reflector for arena usage.

    With portable speedlights, the Guide NUmber will also vary,hugely, depending on the beam spread; at 24mm the GN will be low, at 85mm the beam spread will be narrower and the light concentrated and the GN will be higher; the very-newest top-end flashes have gone to 105mm and even 200mm telephoto beam angles, which give a very,very narrow spread and an exceedingly high GN.

    So...it's hard to put an exact number on speedlight vs studio strobe until you compare apples with apples, meaning angle of beam spreads must be similar. S, look for the Guide Number in the same units at the same ISO, 100 ISO, and only then can you get a reasonable and fair comparison.
     
  4. clockwurk

    clockwurk TPF Noob!

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    Thank you Mike, tis helps a lot :)
     
  5. clockwurk

    clockwurk TPF Noob!

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    Thank you also Darrel!
     
  6. c.cloudwalker

    c.cloudwalker TPF Noob!

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    No comparison so don't don't bother. Would I pay for a strobe if I could get away with using HS flashes? I don't think so.

    Much more important is what exactly you want to do with your lights. If you're going to shoot a few portraits a year in your makeshift studio, flashes and the strobist way will do you just fine. If you are planning to do every day shooting of a studio type, you had better get strobes. And ABs may not be the best choice.

    ABs are the middle ground. Not the best strobes but definitely better than HS flashes.

    Btw, do you know that some softboxes require more than a dozen strobe heads in them? Can you imagine how many flashes you would need to reach that same level of light?

    Better help could come from telling us what you intend to do with the lights.
     
  7. Dwig

    Dwig TPF Noob!

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    Correct. Watt/Seconds (WS) and Guide Number (GN) are measurements of different attributes and, thus, there can be no "translation" from one to the other. Its not "comparing apples to oranges", but more like "comparing apples to a color".

    WS is a measure of the electrical power fed to the flash tube. This is, within a modest degree, related directly to the total quantity of light emitted by the flash tube. GN is a measure of the intensity of the light after it has been diffused, directed, and/or focused by all of the reflectors, lenses, and diffusers attached to the flash.

    Studio strobes generally have interchangable reflectors and other attachments and, as a result, the manufacturer can't tell you a fixed guide number for a flash without some massive table including GNs for each accessory combination possible. Which conventional shoe mounted camera flashes, the reflector and lens/diffuser is fixed making a GN specification practical and most useful to the user. They could spec the WS, but it would be meaningless for any comparison of flashes since no two flashes would use the same reflector/lens/diffuser.
     

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