The camera's hot shoe is compatible with all of the currently marketed Canon Speedlite flash units as well as a number of flashes no longer marketed (e.g. they don't actively sell the Speedlite 580EX II... but it works with it.)
The model number of the flash tells you the "Guide Number" of that flash in meters. For example the 270EX II has a "guide number" of 27 meters. The 430EX II has a "guide number" of 43 meters (just omit the final "0" in the model number and that's the "guide number".)
A "guide number" is an industry standard baseline for measuring how far away a flash can adequate illuiminate a subject. But since the amount of light collected by the camera depends on your exposure settings, the baseline of ISO 100 and f/1.0 (aperture opening size) is assumed. What you _really_ do is divide the "guide number" distance by the f-stop (aperture) of the lens and THAT's the actual distance that the flash can handle.
For example: The Speedlite 430EX II has a "guide numbrer" of 43 meters or about 141 feet. But that's at f/1. Your camera cannot shoot at f/1 (nobody makes an f/1 lens.)
When your camera is fully zoomed-in (maximum magnification) the lens has a focal ratio of f/6.5. So you'd divide 141 feet by 6.5. That gives you a distance of just a little over 21 feet (21.7). If your camera is fully zoomed-out (wide angle) the focal ratio improves and the f-stop can drop as low as f/3.4. So you'd divide 141 feet by 3.4 and that gives you a distance of about 41.5 feet (the distance is better because the lens aperture opening is larger which means it can collect more light.)
All of that was for the Speedlite 430EX II. There's a 320EX and a 270EX II which are both much smaller and more compact... but also less powerful.
One more thing... when a flash is pointed DIRECTLY at your subject, you get a harsh "flat" lighting. The subject casts no shadows because the flash is close to the lens (so the shadows are all hiding behind your subject where the camera can't really see them.) Good lighting includes good shadows and also shadows that have a soft transition from light to dark rather than a well-defined edge of the shadow. While off-camera flash is fantastic, an easy solution for on-camera flash is to "bounce" the flash off the ceiling. This works if (a) you are indoors, (b) the ceiling is not too high (otherwise the distance to bounce is too far and you get very little light back), and (c) the ceiling is a nice neutral white (if the ceiling is painted a different color than the color of the ceiling will tint the light.)
The reason I point this out is because when you "bounce" the flash, you get a more attractive look, but the light has to travel much farther than if you point the flash straight at the subject and also not a 100% of the light gets reflected... you lose a lot of light. For this reason, it's NICE to have a flash which is more powerful than what you might expect.
A 270EX II will work well for bouncing IF your subject isn't very away (e.g. indoor subjects within about 10'). If you're at an event... it's a large room, your subject is farther away... the 270EX II wont be strong enough.
The OTHER time that it's GREAT to use a flash is outdoors in full sunlight. This might seem odd... but the sun is SO bright that the shadows it casts are VERY dark. Shooting a person, for example, gives you an exposure where the bright side of their face is very bright, and yet the shadows are very dark. It's much nicer when the highlight side of their fast is only a little brighter than the shadow side. To fix this, you use the flash OUTDOORS in full-sun as a "fill" flash. I prefer to turn down the flash power just a little... to the "-1" setting (you can adjust it in 1/3rd stop increments.) This really improves the look of outdoor photos.
The menu on your SX50 will have an external speedlite control section which allows you to adjust power levels of the speedlite.
I own a 270EX II, a 430EX II, a 580EX II, and two 600EX-RT speedlites. I use the 270EX II with my Powershot G series body but only as an outdoor "fill" flash or as an indoor flash when bouncing to illuminate subjects within about 10' away. For more general purpose use where subjects might be much farther, I use the 430 and higher models.... especially when using off-camera flash with light-modifiers to soften the look of the light.
Tim Campbell
5D III, 5D IV, 60Da
