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How powerful of strobe needed for large softbox?

Gerard Bianchi , May 24, 2003; 04:49 p.m.

I am planning to buy a large softbox. Minimum of 3ft x 4 ft in size. Possibly 4ft x 6ft. I will also be buying a strobe system to go along with it, but don't have experience with strobes and don't know how powerful of a strobe to get to ensure adequate light coming from such a large softbox. I'll be using it for family portraits. I am thinking of going with 800 or 1200 watt-second strobes, but want to make sure this would be adequate before making the purchase.

Any thoughts on this would be appreciated.


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John Lambiase , May 27, 2003; 12:47 a.m.

Well sir I do not know if I can answer this question but I will tell you what I have. My setup consists of one Alein Bee 400 Strobe (the smallest one they make) I have a 2x3 foot softbox attached to it. The soft Box is one that Alien Bee sells on its website. I will say that this Soft Box is lined with Aluminum Foil and it is Double Diffused. I will also say that For Digital photography I only use it at 1/32 of full power for Still Life Photography. If you are New to Photography then I would suggest Alien Bees becuase they are Cheap but not that Cheap. Not to mention They give you a lot of room to manipulate. It has a 6 stop slide Bar and it has a slave so that really is the way to go. To answer your Question about the soft Box. They have a 72" one and I think my light is powerful enough to use one that big.

Derick Miller , May 27, 2003; 02:10 a.m.

There is a good article that explains some basic issues about studio strobes and has a section on power which will give you a fairly good idea about ws and what you might need:


The short answer is that "800 to 1200" may be quite a bit more than you need. For portraits, you will probably not be shooting stopped down, so even with a big soft box, you won't need a huge amount of power.

One thing you might want to consider is how low you can make the power. Why? Because you may want to be able to open up without having to use ND materials. I believe my boxes are 3x4 and my strobes are 750 ws monolights (travellites) and they provide plenty of power for portraits (and if I want to shoot head shots with the lens wide open and the light source near, I just use the modeling lights and white balance the digital camera ;-).


Mike Dixon , May 27, 2003; 02:13 a.m.

With a 3 x 4 softbox about 6 feet away from the subject, using an exposure index of 80 (100 ISO film), I get about f8 with a 500 w-s monolight at around 1/8th power. Unless you plan to shoot at very small apertures with very slow film, you will have more than enough power.

Larry S , May 27, 2003; 11:22 a.m.

You should note that softboxes work best with stobes that have a reflector that can come off giving a bare bulb effect. This provides maximum dispersion within the box (light bouncing off interior sides of the softbox). Baffels help with this also.

Cecil Thornhill , May 27, 2003; 11:56 a.m.

A lot depends on your format and location. If you are using a large format camera, you are most likely to need very small F stops (like F22 or smaller). If you are using 35mm or a DSLR you will most likely not want to work at more than F11 or 16, and you might work a lot at F5.6 or lower. In a studio where you can get the strobe more than 10 feet away, you need lots more power, and of course the larger the source (softbox) the softer the light - so at a distance you may find you want a panel more than a box. You also might diffuse the softbox with a panel sometimes too, and that might need more light. I find I get F11.5 from my 3' x 4' white interior softboxes with an ISO of 100 at about 10' from an 800 watt second Dynalight pack and a LiteLight bare bulb style head. I agree with those who suggest minimum power is as important as maximum power - for portraits or still life, I find even 100 watt seconds can be too much. Still, when I am on a location and I need to light up a big space with lots of people in it, I find having 800 watt seconds is a great help. I would seldom need 1200 on one light right now, but if I was doing furniture I think I might want even more. Dark subjects can drink up your light. If you plan to work on mostly portraits, I would suggest 400 watt seconds might work just fine. Remember, for many lighting styles you will have key and fill on the highlight side, so the total exposure will often be greater than that provided by any one light.

... Timber ... , May 27, 2003; 11:22 p.m.

A softbox will "waste"2 stops worth of power: Your 800ws unit will become effectively a 200ws unit. With 200ws you can illuminae at a luxurious distance with that 4x6 box. This will give you an f8 on a group shot of 5-6 people. Perfect! For a single person, you should be using f5.6 so that you get a moderately blurry background. Therefore you can reduce power. If you use negative film or digital, you don't need the preciseness of a slider bar to control power. Therefore you don't need Alienbees, Balcar, or other expensive monolights. I think you will be happy with a studio pack and a large reflector made from FH1018. A p1250d Norman pack is cost effective. Go to www.ahh.biz for this silver mylar canvas vinyl ($10 yard). Timber Borcherding timberborcherding

... Timber ... , May 28, 2003; 01:57 p.m.

In response to John's comment on Alienbees; using it at 1/32th power. While I like these units, be aware that 1/32th seting is only about 9 (nine) watt seconds! Through a softbox this becomes about 3 ws! The B400 unit is a 150 ws unit which is pumped through efficient Balcar reflectors for a 400ws rating. Take away these Balcar reflector, and you have less efficiency! This unit has only one 1250uF capacitor! Good for a "kicker" or hairlight, but useless for ANY softbox. Consider looking at a used Brownline Speedotron pack 1200 ws unit! Hey, I bought a used Norman unit1200ws yesterday for $175! Timber Borcherding timberborcherding

Russell Britt , May 28, 2003; 10:25 p.m.

I used a 4X6 soft box with a old phoogenic 400 watt sec unit set on 1/2 to1/4 power for portraits. If you use a large softbox you put it very close to the subject. If you move it back it is not as soft so you have gained nothing.You do need a bare bulb type flash head.

Jeffrey Moore , May 29, 2003; 12:16 p.m.

Gerard, I will throw in my two cents in hopes that it will help.

I am a big fan of AlienBees strobes, manufactured and sold direct by Paul C. Buff Co., in Nashville, Tennessee. They also make a higher-end product, White Lightning. In my opinion, in terms of the dollars vs. performance relationship, the AlienBees represent the very best value currently available in monolight strobes. Moreover, you can try them literally risk-free, as they have an unconditional, no questions asked, 60-day money back guarantee. Their reputation for customer service is legendary--and well deserved. (I am in no way affiliated with the company, just a big fan of their products.)

Here is what I use for my own studio portrait work and how I use it, in the hopes that it will give you some guidance on what you need.

I use a typical 4-light setup: My main light is an AlienBees B800 with their giant softbox, which is 30" x 60". My fill light is also a B800 with the large softbox, which is 32" x 40". I use a B400 with a scoop-style deflector to light the backdrop, and another B400 with a honeycomb grid as a hair light. I shoot both medium format film and digital (Nikon D100).

Shooting the Nikon D100 at ISO 200 (or ISO 200 film, for that matter), with the above mentioned setup, I will shoot at f5.6 to f8. I will have my main and fill lights in typical arrangement at about 5-6 feet from the subject. The AlienBees have variable output from full power down to 1/32 power, a five-stop range. Assuming a typical 3 to 1 (stops) lighting ratio between the main and the fill lights, in this setup, shooting at f5.6, I will have the B800 fill light at 1/32 (that's minimum!) power, and the main light at 1/4 power. One point to emphasize here: in this setup I don't really even need the B800s for my main and fill lights; I would be fine with the B400s. The B400 represents a 1-stop less powerful light than the B800, so instead of my fill light at 1/32 and my main light at 1/4 power, with the B400s the fill and main would be set at 1/16 and 1/2 power, respectively, to get the equivalent result. Keep in mind that this is with the main light mounted with a 30" x 60" softbox, and the fill light mounted with a 32" x 40" softbox. In my shooting environment, which is relatively small, I can't move my main and fill lights much more than about 6 feet away from the subject (which you don't really want anyway). In my setup described above, using the B800s set at 1/32 (fill) and 1/4 (main), at ISO 200 I can't even shoot at f4 because it's TOO MUCH LIGHT!!

With all due respect to Timber, his comment that the B400 is "...useless on any softbox." is simply false. In fact he couldn't be more wrong, even if his objective was to be as wrong as he could possibly be.

Gerard, if you need more help on deciding how much power you need in some strobes, Paul Buff has written a great little 25-page booklet titled "Lighting For Still Photography." It's not a sales brochure, but a scientific explanation (but written for the layman) of studio lighting, lighting ratios, etc. After reading this booklet, you will be able to decide for yourself how much power you need for your particular situation. It's a great help. AlienBees (or White Lightning) will send you a copy for free (1-800-443-5542).

Hope this helps. Good luck!

Jeff Moore

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