How much flash power do I need?

I am building a small portrait studio (you may have seen other posts of mine) and I will be using Hasselblads with BW film. I am trying to decide on the power of the strobes I will need.
Considering that I will be probably using film speeds between 50 and 100, appertures between 2.8 and 11, softboxes and umbrellas and distances no further than a meter or two, would 500W be enough, or should I go for more?
I am not planning to develop to a large studio, as my work will be mostly photojournalistic and not fashion or commericial, so I am not sure if I will be needing stronger lights in the future. Furthermore, a large format camera is not in the present budget or even a thought as I prefer to master my present equipment before moving to something else.

Power - it's tough to have too much.

Part of the problem in choosing studio strobes is that watt-seconds (WS) is a somewhat unreliable measure. Different units put out different amounts of light using the same input power. Generally speaking, however, something around 600-800 WS, assuming the use of softboxes, is usually sufficient for general portraiture. A good softbox will eat a couple of stops, but it's well worth the power consumption. A more fundamental choice is whether to go with a power-pack unit, or monolights. The practical side of that may rest with what's available in your area, and then "working around" whatever limitations it has.

There is a chart on the WhiteLightning site (http://www.white-lightning.com/) that gives the outputs for their units, along with what that translates to in terms of shooting apertures with different light modifiers. The chart may help to give you a better handle on the equivalents, Ari.

500 watt seconds may well be adequate power at the distances contemplated. What I would give very serious attention to is recycle time. I would find a recycle time of two to three seconds highly desirable.

It depends if you want monolights or pack & head.

For monolights, you could probably get away with 400ws units, but 800 would give you much more flexibility in light placement, 1600 that much more.

If you're wanting a pack & head system, I'd go for as big a pack as I could afford and still be able to buy heads!

I use anywhere from 1 to 5 monolights when shooting portraits (sometimes as many as 8!). If I were looking to buy new, I'd look at the White Lightning X1600 units.

You could get by with 500 W-s, but something like a 600-800 W-s pack system, as Ralph recommends, will give you more flexibility.

Start with about half a teaspoon and see how that goes.

Best,
Helen
PS You missed the 'd' out of 'powder'.

Well, I had a couple of 600 watt White Lightnings X1600's that I shot thru a double diffusion Photoflex medium softbox and I was always in the lower power range of the 2 closer to the weak end. I was shooting at about 8-9 ft away for a full length. I feel that 400 to 500 should cover well, especially if your doing alot of head and shoulders, as a soft box is softer at closer working distances, and you'll blow the sitters eye's out, so you have to dial it down. I prefered to shoot around F8, even F5.6 (with 35mm) because of this. One problem I had was I couldn't get the dark background far enough back at 5ft and got some light spill so be mindful.

Personally I prefer outdoor portraits. It's a little hard in the heat of the summer, but much cheaper to get started. For outdoor stuff a little fill light is all you generally need. Because of this I have since gone to battery dependent flashes which are also nice for in home setups during the rainy and hot months. Light packages that are small to carry and fast to set up are the way to go as far as I am concerned. You'll never know where you'll have to setup to shoot, so don't think that your always going to stay planted in a studio. In fact, I'd buy with traveling in mind and use them in a studio.

The WL's are a really nice kit and their literature that's available titled "Lighting For Still Photography" is the best information I have ever read on the subject of studio flash techniques. Btw, their support is the best.

Thank you guys.
I am considering either Hensel or Elinchrom three monolight sets.
The Hensel would be 500/250 and the Elinchrom 300/600.
If I go higher I would probably go for Hensel 750/500 or Elinchrom 1200/600.
Both brands offer pretty advanced monolights, with fast under 2sec recycling times,
6 stop digital range, etc
The Elinchrom ones are lighter but the Hensel seem sturdier.
The White Lightning is not available in Greece.

If it is not just about power ... I use DynaLite MX1000s and I've never needed more power - I have found Neutral Density filters to be useful. One thing is sure - it is easy to subtract light, but really difficult to add any on if you need it.

Weight is, to me, a MAJOR consideration... The DynaLite #2040 heads are light .. far lighter that any monolight ... and I really would like them to be even lighter when they are hanging out on the end of a boom. One really NEEDS the boom counterweights and the problem is worse with more weight. Also consider the ease of control. If you can, get whatever remote you would need to adjust the output of the monolights in place. Sooner or later, you will get into a situation where you want to change the power output, and unless you have some sort of remote control, you will have to disassemble part of the setup to reach the controls.