How can I blow out the background with a single flash?

Question

I have a Yongnuo 560 ii flash that I usually use to light my white backdrop for clothing shots on a model. The issue is sometimes it doesn't make the whole background white. Either blows out the side where I locate the flash or only the higher area... all depending where I put the tripod that holds it.

I was wondering if using an umbrella can help me expand the light to the whole background and also what intensity to use in the flash so I can blow out as much background as possible.

Will it help if I place the tripod further from the background so the light expands?

Answer 1

You're making this way too hard. You don't need to light the backdrop perfectly evenly. If the dimmest area of the backdrop is blown out the rest of the backdrop will be equally blown out. There is no shade of white brighter than blown out.

Here's the problem with using an umbrella to diffuse the light or moving the light further back: You're lowering the amount of the flash's output that makes it onto each square inch of the background. That's going to make the backdrop dimmer overall. This means you're more likely to get varying brightness levels from different parts of the backdrop.

The key to getting uniform white backgrounds isn't illuminating them evenly. It is making sure the dimmest part of the white background is lit bright enough to be pure white with the ISO and aperture you are using. (Shutter time matters also for constant lights but not for strobes since the strobe's duration is usually shorter than the camera's sync speed.)

It doesn't matter if one side of the backdrop is getting more light than the other. You just need to expose in such a way that the dimmest part of the backdrop is completely blown out. You'll find this easiest to do if the flash lighting the backdrop is at full power (assuming it isn't too bright as to create a lot of spill back onto your subject).

If the dimmest part of the backdrop is pure white in your resulting photo the entire backdrop will be pure white. There's no way for the brighter parts of the backdrop to be brighter or whiter than pure white in the resulting image.

Once you've got the exposure right for the backdrop you can then adjust the power of the other light(s) to properly expose your subject at the same ISO and aperture.

Answer 2

In your case it might help to change the angle of your backdrop, so that every point of it has roughly the same distance to the flash. So if your light comes from the right, move the right side of the backdrop further away from the camera.

Of course, the backdrop has to be big enough for this. Also you can only compensate for the left-right gradient in the background, top-bottom would be a bit more difficult..

Answer 3

all depending where I put the tripod that holds it

Ok I think the answer is... change where you put the tripod that holds it.

But I assume this is limited due the total space between the model and the background.

If you increase the distance between the model and the background you have space to put the flash directly behind the model. Experiment with distances, for example if your model is 1.5 mts tall, put your model 1.5 mts away from the background and the flash just behind. Try other distances for example 1.5x or 2x the height of the model.

This distance also helps reducing the reflected light to wrap arround your model.

Aditionally very important!:

• Change the zoom range on the flash to the smallest number. That makes the light spread more.

• Pull the little transparent grid the flash itself has and leave it infront of the flash strobe.

• Use the flash in the same orientation as your image.

• You can also use a pice of vegetal paper in front of the flash.

As you are using the flash exactly behind the subject you can not have an umbrella.

If you want to use an umbrella you need more than one.

One important thing is that you can not use a very wide lens... Imagine you want to shoot with a fish lens, of course at 2 mts you can not have an even backdrop. Try to use at least 50mm lens. The longer the better.

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You need first of all to learn how to take a photo of a simple white background with no model. The result is a pretty boring white photo, but you need to know it.

This distance afects the total brightness of the background. Start for example at 1/32 the total power of the flash.

At 1.5 mts away and 1/16 I can blow a white background at f5.6. Iso 400 (rough estimation).

So you have room to play: f/8? use 1/8. f/11? Use 1/4.

It is also important that your background is white and diffusive.

A coated paper or plastic is NOT good. This makes hotspots and the edges look gray.