How to determine the Wattage needed with strobes(flash)??

[pablovi]

Hi, I've never used Strobes, infact I don't even own one, I come from

Cinematography so I own many continuos lights, tungsteng and some

Kinos(Flourecent) and I do know how to determine how much wattage I'm

going to need with continous lighting, but since I have never used

strobes I don't know how to do that with them.

 

I need to know what to buy, I'm going to do primarily Fashion and

Portrait with the strobes, probably I would still use the continous

lighting for product, but I don't know ho much light 200W/s is or

1000W/s.

 

I don't know if this made sense but it's hard for me to explain it in

english, basicaly what I would like to know is how much wattage do I

need for shoting outside and in a studio, I know with continous

lighting that I need at least a 4K HMI PAR to use it as a key light

outdoors like 4 or 5 ft from the actor. If I need to cover more space

and from a greater distance I would probably use a 10K HMI Fresnel or

something bigger, even as much as an 18K HMI Fresnel.

 

So I don't know if 1000W/S is enough from a strobe to use it as a key

light outdoors, and if 500W/s is enough for all studio work, or if I

can get along with less W/s in studio? I hope I made sense. And Also

what Strobes do you recommend? (best for the price)

 

Thanks in advanced, and sorry for the lenghty post.

[johnmarkpainter]

Pablo,

 

Here are the variables: Light Modifiers,Film Speed, Format, desired Apertures, Subject

Size, Studio Size, Subject to Light Distance.

 

What I did....I bought 4 Alien Bees lights. (2) 400, (1) 800 and (1) 1600 (those aren't the

tru W/S ratings by the way).

 

Many people will tell you to just buy the brightest lights you can afford, but you have to be

able to turn them way down for some applications or even have neutral density Filters.

 

It is good to have at least one high power light to use in Large Softboxes or an Octabank

for instance (the 1600). It is good to have two lights availlable for Background (they

usually don't need to be as powerful in my usage...I use the 400's). Then I have the 800

that I can use as Fill or use with a Snoot or Grid.

[pablovi]

Thanks John!

 

Ok, I'll probably use most of the lights through some kind of difusion, I have 2 Video Pro bank Chimeras and one Chinnese Lantern Chimera, I will work with medium(6x4.5) and 35mm format, and the film speed I guess I will be using severals emulsion, but I like to work with 50 or 100 ISO.

 

Thanks for the advice, Is the 1600 strong enough to be a key light outdoors through a Chimera? and have the sun as a backlight?

 

What are Alien bees lights?

 

Thanks again

[peufeu]

What you can do with flashes, that you can't do with continuous lights, is balance the flash vs ambient ratio using the exposure time.

 

The flash is very fast (1/500-1/10000 s), so you always get the full light of the flash on your film/sensor (just take care about the camera sync speed) and then you adjust your exposure time to let more or less ambient light, as you wish.

[pablovi]

Thanks Pierre,

 

Yeah, I know you can do that, but only if the Strobe is powerfull enough for you to get an exposure, that's what I was asking, what wattage is enough fo you to get an exposure at 60 Speed outdoors. I know I can't take a 1000 Watt Fresnel(Continous) and get an exposure outside with it.

[miles_feigenbaum___dallas_]

http://www.lightingmagic.com/

[bill c.]

Pablo-- Technically, a 1,000-watt-second strobe unit will allegedly put out the same amount of light per flash that a 1,000-watt continuous light will put out for one second. Note that this is a rough guide, and will vary depending on the efficiency of the unit and manufacturer, but the same will be true of incandescents, too.

 

This means, for example, that if you measure the light output from a 1,000-watt incandescent, and with your meter you determine that the correct exposure is f11 at one second, then a 1000-watt-second flash unit at full power with the exact same reflector/lightmodifiers at the same distance (etc. etc., all factors being equal), f11 would be a good starting point for a possible exposure for the flash. Kinda maybe.

 

The respondent who advised you to get the most powerful unit you can afford which has the ability to dial down power is probably the most practical effective advice. The more power you have, the more heads you can use and the more modifiers you can utilize and still retain enough power to overcome sunlight. I find that about 2,400 watt-seconds is about enough for small sets to balance sunlight. I wouldn't want to do anything larger than a ten foot width without twice that power.

 

The higher shutter speeds will help- but only up to a point. Many high-end strobe systems will have their output time fixed at between 1/300 sec. (Comets, for example) and 1/800 sec. If you are using those systems, any shutter speeds you use that are higher than the flash duration will cut off part of the flash.

 

Happy shooting. -BC-

[shiver_me_timbrrrre]

A 1000ws flash consumes about as much electrical energy as a 1000w continuous light in 1 second but one cannot determine from that that one will put out the same amount of light as the other. The 'ws' rating on a flash is its electrical energy storage rating; it really tells you nothing about how efficiently it converts that energy into light.

 

As a second example, let us compare a 1000w tungsten-halogen Fresnel luminaire with a 1000w HMI Fresnel luminaire (if there is such a thing as a 1000W HMI lamp). Do they put out the same amount of light? They certainly consume the same amount of electrical energy in one second. It is commonly accepted that watt for watt, an HMI luminaire is about 2.5 times more efficient into turning those watts into lumens of light than a similar tungsten halogen luminaire.

[indraneel]

Paul C. Buff of White Lightning and Alien Bees explains some technicalities here:

<a href="http://alienbees.com/manuals/bluebook.htm">http://alienbees.com/manuals/bluebook.htm</a>.

I guess it will depend on the length of the flash your strobe puts out. Probably around 1/1000 or faster considering that the D70 can sync at 1/500.

[robert_hall2]

Wattage is not the answer. Guide number is. For example, if the GN is 110 at ISO 100, you would use f11 at 10 feet. GN = f-stop X feet. The metric guide number is available from reputable manufacturers. Guide numbers are often exaggerated by some manufacturers. The two main brands of commercial-quality lights seem to be Norman and Photogenic but there are a lot of others, some cheaply built.