"Lighting Lingo" Question

jasoncaine · November 27, 2007

I am interested in purchasing some basic lighting for small studio photos (groups of 4-6 max), etc. I am a bit confused on the "lighting lingo", though ...
If something has a guide number of 100 at ISO100, what exactly does that mean?
The recycle time I understand - takes 4-6 seconds for everything to ramp back up before they can fire again.
But what is really confusing me is the 2, 100 second watt flashes ... I know that it means that it comes with two, but what exactly does "100 watt seconds" mean?
Is that any good ... or am I wasting my money?
Looks as though ny lighting will be a decent investement and I don't mind spending some money on it ... I just don't want to waste money on it! Any advice would be greatly appreciated!!

This is the description of the unit in question if that helps in your responses:
Studio Monolight Flash Kit #1 with 2, 100 watt Second Flashes, Light Stands, Umbrellas and Softex Carry Case
Product Description:
The Budget light unit screws into any standard household light socket. It has a circular flash tube that is daylight balanced at 5600 degrees K, a guide number of 100 at ISO 100 and a recycling time of 4-6 seconds. It also comes with a 60 watt removable modeling lamp. The Budget Studio Flash can be triggered through the camera with its 12' sync cord (included), by another flash being fired and activating the built-in Photo-Slave, or through its open-flash test button. It's a compact 6-1/2" long with a diameter of 3-1/2" and weighs only 15 ounce

dogwood · November 27, 2007

Guide numbers and watt seconds are a way to describe the power of your strobes when they flash.

100 watt second is not very powerful-- unless you want to shoot everything at f2.8 and ISO 400

Check out the alienbees.com website for good deals on decent equipment and also explantions of watt seconds. I might be wrong about this, but guide numbers are usually used in portable hotshoe strobes.

Anyway, just keep in mind when buying that you can always turn down the power on a powerful strobe (or move it or diffuse it) to get less light on your subject, but you won't be able to similarly increase the power of a not-very-powerful strobe. In other words, buy as much power as you can.

jasoncaine · November 27, 2007

So if something offered 300 watt seconds I would be far better off as I could always dial it down a bit if needed? Is there a formula for calculating out the ISO and aperture based on watt-seconds like you did or is that just something that you know by experience? I have a better idea of what the watt seconds mean now, but am still trying to wrap my brain around the guide number ... what does that represent?

dogwood · November 27, 2007

jasoncaine wrote:

Is there a formula for calculating out the ISO and aperture based on watt-seconds

I use a formula called a Sekonic 358 meter

Works great at balancing ISO, shutter, and aperture.

Seriously, I've never been very good with ratios or watt seconds or guide numbers-- but f/stops make perfect sense to me. So I just meter everything I shoot unless I'm shooting an event and using ETTL and a hotshoe strobe. Even then, I occasionally set up a light and meter in a known location (for example the end of a fashion runway).

Yeah, the higher the watt seconds the more power you're going to get. Without getting too technical (really), I used to have two AB 400's (180 true Ws according to the website) and found them too weak for a lot of what I shoot. I still have a couple of AB 800's but at times (especially shooting them through a modifier like a softbox) I still struggle to get more than f5.6 at full power. And using a lens at 135 mm (fairly standard for portraits), there's often not enough DOF to keep all the facial features in focus.

So... that's where my advice about buying the most power you can afford comes in. I'd happily trade those AB 800 for a couple of WL 1600's (besides, I like the metal WL housings more than the plastic AB's).

And not to drag you away from this forum, but the alienbees.com website does have a forum and the AB/WL owner frequents it. He's a total geek (in a very good way) about lighting and can probably help you out.

pathfinder · November 27, 2007

You can read about guide #'s here.

A guide # of 100 at ISO 100 is not very strong.

The Canon 580ex has a guide # of 190.

The formula is {Guide Number/distance in feet} = fstop -- The shutter speed is assumed to be brief ( ~1/160th) and conveys no significant ambient light to the sensor.

Thus, 100/ 8 feet = f 12.5

100/12 feet = f8.3

"Lighting Lingo" Question

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