A photographic umbrella (also know as a brolly) is exactly what it sounds like. It is the same basic shape as a typical household umbrella. Instead of repelling water though these are designed to either bounce, reflect or soften a light source.
In this post I'll discuss the two basic umbrella types. Shoot through and bounce. I'll briefly describe each type and how it is used.
The bounce umbrella:
With this umbrella type, you point the flash into the umbrella and the umbrella directs the light back towards the subject your pointing the umbrella at. The easiest way to determine where your umbrella is going to focus the light, is line up the metal umbrella shaft to the center point of where you want the light to hit on your subject.
White Bounce Umbrella:
There are different results from different colored umbrellas. Unfortunately I don't have every type of umbrella to give you a visual. So I'll briefly tell you what each color type does and the best application for it.
Out of all the colored bounce umbrella's, this will produce the image w/ the least contrast and the softest light because the majority of hard light is eaten up in the white reflection material.
Best applications: Main lighting of portraits, lighting backgrounds.
This will produce an image w/ the most contrast and the hardest light (along with any other metallic type reflective material). Opposite of the white bounce, almost all the light is focused back to the subject w/ next to no light being 'wasted'.
Best Applications: Rim lighting, keeping light focused without excessive "light spill".
This will give you the same amount of contrast in an image as a silver brolly. It will give a warmer cast to it though so this type of umbrella can be good for outdoor shots when you want to try and balance the flash to the sun.
Best Applications: Outdoor daytime light balancing. (A.K.A. fill lighting)
I honestly haven't seen a grey used well in an application yet. I'm sure there's a good reason out there to use them. If you know, please post a comment w/ a link or email me and I'll update this post.
NOTE: I prefer gels to change color temp instead of brollys. This way you can carry and buy less. (I'll link this note to gels when I make that post)
The shoot through umbrella:
This is a great portable way to really soften light from a flash and give you the softest possible light w/ using an umbrella. The material is usually white but it is very easy to change the color of the umbrella by just placing a gel on flash.
Side view of a shoot through umbrella:
What you should know about using umbrellas:
There is a common misconception that the larger the umbrella you use. The larger your relative light source is and the softer your shadows will be. This is only partially true. Another major contributor as to how large your relative light source is the amount of light that hits your umbrella. I will show you a few images to show you exactly what I mean.
NOTE: While I am only showing examples of the shoot through brolly for these images, the principal remains the same for any light diffuser/reflector. I will also only use one umbrella size so you can take these images at face value and don't need to consider different sizes.
In the following image you see the back of a 43" umbrella w/ a flash being shot into it (this is the same exact setup as the previous image shows).The zoom on the flash is at 85mm (telephoto). Notice how there is one concentrated area where the light is mostly focused? This is the real relative size of the light source that your using.
While the light spilling outside the area of this 'hot spot' is still helping light your subject. This excess light is barely noticeable and at this point in your lighting won't make any difference.
In the following image you see the back of a umbrella w/ a flash being shot into it. The zoom on the flash is at 85mm (telephoto).
In the following image you see the back of a umbrella w/ a flash being shot into it. The zoom on the flash is at 24mm (wide angle). Notice how the relative size of the light source is much larger than the previous image?
What does this mean to you?
No matter how large your umbrella, if you don't have a light source that can fill it, you are not utilizing the entire umbrella's ability. So buying a 60" umbrella won't necessarily give you a 60" light source.
More ways to control the size of your light:
As mentioned before, a bigger light source is not always better. I've shown you how to use the zoom on your flash to control the relative size of your light, another way to control the size of the light is to bring your umbrella closer to the umbrella. How you do this is slide the umbrella all the way into the umbrella adapter as far as you can make it go, so the flash is closer to the actual umbrella.
In the following image you see the back of a umbrella w/ a flash being shot into it. The zoom on the flash is at 85mm (telephoto) with the brolly as close to the flash as possible. This setup gives you a very small relative light source.
In this image you see an umbrella w/ a flash being shot into it. The zoom on the flash is at 24mm (telephoto) with the umbrella as close to the flash as possible.
How to make your umbrella last twice as long.
I learned this trick from a blog posted by Rui M Leal from Portugal. He has gone into excruciating detail as to how to do this DIY so I won't steal his thunder or re-invent the wheel. But I'll give you the skinny on what it is and how it works for you.
Most common umbrella shafts are made with a hollow octagonal shaft. The inside diameter just happens to be a hair larger then the size of a standard #2 pencil.
All you do is measure the length you need to slide into the core of the umbrella shaft, cut the pencil to size, put a little glue on the pencil, then slid the pencil in! Now you have a solid core instead of a hollow one. You'll find this especially useful when you clamp down an umbrella for the first time and see how the retaining screw on the umbrella adapter seems like it will sandwich your hollow umbrella shaft!
Here's a shot of the end result on one of my umbrellas. I prefer using gorilla glue since the stuff is made on mars or some place where the glue Gods have got some serious skills.