Strobists: Stops of Light

Guys ... How many stops of light are lost when you place a flash inside a soft box?

What sort of flash unit are you considering?

What sort of and how large a softbox are you considering?

Hi Skip. I've got a Nikon SB-700 flash and a 28" Westcott softbox.

Now somebody may be able to feed you some real data. I don't have either of your devices so I cannot be much help.

ChillOne wrote in post #15929173
Guys ... How many stops of light are lost when you place a flash inside a soft box?

Depends on the flash as well as the softbox.....
You will need to use a light meter to figure that out.

One or two diffusion panels, were is the light positioned in the Westcott? What is the zoom on the speedlite?
All may contribute to the answer.

As everyone else has indicated there are soooo many factors that play into this.

Yes, as stated, it will vary, but here's a couple of data points from a test I ran recently. I was using a Canon 580EX II, a Westcott 60" reversible umbrella configured for reflective use, and a Sekonic L358 light meter. The light stand with the flash on top was about 8' from the point of measurement. For the umbrella tests, I just spun the speedlite around to face the opposite direction, so add a couple of feet from the inner surface of the umbrella at the shaft to the measurement point. All tests are at ISO 100.

Direct: Flash head aimed at light meter, full power

-Head zoomed to 105mm - f/14
-Head zoomed to 24mm - f/9

Reflective: Flash aimed at 60" umbrella, 180 degrees away from light meter, full power

-Head zoomed to 105mm - f/4
-Head zoomed to 24mm - f/4
-14mm diffuser panel lowered and umbrella moved closer to head - f/3.6

So it lost about 4 stops. I think a softbox would likely lose more due to the diffusion panels and lack of spill light to get out and bounce off a wall to contribute to the exposure.

By comparison, the Alien Bee 800 I was testing against only lost 2 stops. Remember speedlites are meant to be aimed at the subject and zoom to concentrate their power on the subject. In that mode, the speedlite at 105mm was only 2/3 stops weaker than the Alien Bee. But once you add start bouncing and diffusing, the speedlites really lose their punch.

Its about a 1/2 stop just for the fabric cover over a quadra head. So the fabric is about a half stop, but where you place the flash inside and your zoom will change the other factors.

It depends on the softbox construction. At least one stop is absorbed by the softbox, but some have heavier defussers. You can test with a light meter.