What is the purpose of a modeling lamp?

I have what may be a newbie question for all you portrait photographers.

What is the purpose of a modeling lamp, and how can it be used in measuring exposure for my flash units when doing studio portraits?

I have set up a main light, which is a canon 580EX. I am using a reflector for the fill light, and I dont know what I will be using for a kicker light just yet.

What would work for a modeling lamp without spending a lot of money, and what should I be looking for to help me gauge exposure of the subject correctly?

Thanks! :)

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Originally Posted by njmanigan

What is the purpose of a modeling lamp, and how can it be used in measuring exposure for my flash units when doing studio portraits?...

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Modeling lamps can serve several purposes, depending on how you use them. First off, when a part of an external flash unit, the lamp's main purpose is to give you an idea of what the flash illumination will be, especially in relationship to other flashes in the scene.

IOW, when your modeling lamps are proportional, it helps setting up a lighting ratio...

Now, because it's a light source, you can actually light a scene or subject with just modeling lamps if you want to, and not even employ the flashes. But, as most modeling lamps top out at only about 250W, that can be a bit of a challenge. Still, I've done it with good results.

Another trick is to mix the tungsten modeling lamp on one flash with one or more other flashes, much like you would with any hot light. This is easier, as you have more leeway using a slow shutter speed, knowing the main flash will still freeze your subject.

In addition, a modeling lamp helps a great deal just seeing (composing) and focusing in an otherwise darkened studio. It also helps open up a subjects pupils to get better looking eyes in the actual flash shot.

Now, as far as metering your flash units, the modeling light does nothing. You will need to either use a flash meter, have a flash set on auto with a TTL system, or make an initial guesstimate and adjust output/exposure based on reviewing your shots.

Hope that helps. Any other questiosn, let 'em fly...

Thank you very much for the detailed reply! :)

Is there a way I can use the exposure meter on my 30D? I wouldnt think so, because if I try to get a correct exposure by pressing the shutter half way, its just exposing for the existing room light.

So then, I will need a flash meter. I dont have studio strobes. Im just using a 580EX, and a reflector. So, what would you recommend for a flash meter that is independent of my equipment, and how would it measure the amount of flash I should use for correct exposure?

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Originally Posted by njmanigan

So, what would you recommend for a flash meter that is independent of my equipment, and how would it measure the amount of flash I should use for correct exposure?

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I'm not familiar with the 580ex, but being a Canon flash, it should work in some sort of automatic mode with your 30D. Now, how creative you can get in that mode I can't say.

A decent stand alone flash meter will run you at least $100US, the better models going for about twice that and more. Yes, an investment...

njmanigan, this is a few days past your post but hopefully you will see this. I found a website that explains all about the Canon flash system and how to make it work. Go to http://photonotes.org/articles/eos-flash/ (copy and paste it), and be prepared to read for a while. There is a wealth of information on that site. Hope it helps.