3000 W-s is a general guideline. For a really sharp, relatively close portrait (say about head-and-shoulders, more than a really tight headshot), if you want a very sharp look, you need about f:45-64. If you use umbrellas or softboxes, they'll eat about two stops, so you need a lot of light, if this is your goal.
If you are just interested in getting the eyes and nose in focus, and it's okay if the ear is not, then maybe f:32, and if you don't mind the nose out of focus, f:16 or wider should work.
Alternately, if you're shooting Hollywood style with fresnel strobes, these will concentrate light output rather than diffuse it like a softbox, or if you use plain reflectors for a harder look than an umbrella, you can get by with less power.
More power gives you more options.
What David has written above is right on. Also to your previous question as to using strobe for fill etc. Yes you can to that, remember you will probably in that situation (outdoor in shade, or reflected light etc) be using a very slow shutter speed, in that case your fill strobe would register and your shutter would remain open recording the ambient light.
Look at Avedon's "IN THE AMERICAN WEST" these are 8 x 10 portaits taken outside in the shade without strobe. The photographs are sharp throughout.
The subject is about 4 to 5 feet from the lens, as is the photographer...
To quote Avedon...."I use an 8 x 10 camera on a tripod....I stand next to the camera, not behind it, several inches to the left of the lens and about four feet from the subject"
..."I photograph my subject against a sheet of white paper about nine feet wide by seven feet long that is secured to a wall, buidling, sometimes the side of a trailer..I work in the shade because sunshine creates shadows,highlights, accents on a surface that seem to tell you where to look. I want the source of light to be invisible so as to neutralize its role in the appearance of things".
Thanks David and Dave.
Im going to see if i can find some examples, saw one in a magazine i need to scan that and put it online, that look is very sharp, but probably shoot with something smaller or d*****l. But i have seen portable a system with 2x1200 w, so its getting me closer.
Would i need to sync the flash to "rear curtain" if i have ambient light and need to go for a slower speed than the strobes can handle? Or is it ok to sync in on the front one?
for large format i.e 8 x 10 and larger .. no curtain and your shutters are synched at every speed....as the flash is faster than the shutter, your shutter is still open after the flash stops and can expose ambient light....if you want...
Dave's description of the sync is accurate. It is possible with a Pocket Wizard, I believe, to make the flash sync at the end of the exposure with a long exposure and leaf shutter, but it's kind of a special effect for recording flash and motion together. Most people don't need this.
Note that Avedon's portraits are usually three-quarter or full-length, so he can get the whole subject in focus on 8x10" with a wider aperture. If you're interested in full-length portraits (bellows factor will be about 1/2 stop on 11x14"), you won't need as much light as you would for a head-and-shoulders portrait (bellows factor about 1.5 stops on 11x14").
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Originally Posted by bherg
In your country you might want to contact Profoto for technical information, or maybe even drop by (they are in Skarpnäck at Flygfältsgatan 4)
Telephone 08-447 53 00 and ask for Ronnie Lind. He is a technical representative, not a salesman. The information you get will be useful for any brand (but Profoto makes nice equipment, if you can afford it!)
Hope this is helpful to you.
With largish reflector on my Bronocolor Multicom 80 (600 Ws) I get f/32 at one meter. A silver umbrella will be about the same or maybe half to one stop less. A softbos with two diffusing cloths will be f/22 or f/16. These are approximate f-stops for my approximate distances.
600 Ws seems too little for 8x10 or bigger. Two strobes could be combined maybe?
Be careful his bow tie is really a camera
I just get by with 750 W/S per head, with a two flash kit for maximum output when shooting 8x10 portrait work. But even then, I've got very limited depth of field with a 14" Commercial Ektar. I think I'm getting somewhere in the region of F22 on full power with my main light in a 36x48" softbox, with my subject 4 feet (1.3m) from the light.