Lighting Help

[kipalari]

I know these two images have been photoshopped a lot, but how strong of a strobe do I need to achieve a look such as this one, to overpower the sun:

http://img104.imageshack.us/img104/9392/picture6e.png

I'm looking to purchase some equipment to do on location work similar to the images above. Anything will help. Thank you

 

[Garbz]

Not a very strong one at all. A basic hotshoe flash can overpower the sun. The idea is to shoot at fast shutterspeeds as this doesn't affect the flash but does the sun. If you have a D40 or similar camera with insane sync speeds then an even weaker flash can be used.

The problem you may have with achieving the above effect using small flashes is that light modifiers like softboxes or umbrellas will chew away a lot of power.

 

[Big Mike]

The basic principle is fairly simple...but it may be pushing the limits of your equipment.

As mentioned, you can do it with an average hot-shoe flash but sometimes it takes a rather powerful flash.

The first key point is the max sync speed of the camera. The faster the shutter speed, the more you can cut down the exposure from the sun. So if you could sync your flash at 1/2000, it would be easy. Unfortunately, most DSLR cameras are limited to 1/200 or 1/250.
So if you are shooting out in bright sunlight and you are limited to 1/250, then you may need a small aperture to get the ambient exposure down to where you want it. For example, you might require F16.
Flash exposure is directly related to the aperture, so as the aperture gets smaller, you need more flash power or your flash's range gets smaller.
So shooting at F16 and ISO 100, a typical flash may only have a working distance of 6 feet. So as long as you understand how much range you have, then you should be able to overpower the sun with your flash.

Also, as mentioned, light modifiers take away a lot of power from flashes, so it may not be a good idea to use them in a situation like this.

This is where a pro shoot might require some powerful studio strobes, so that they can use a softbox while still overpowering the sun.