What am I looking for in a flash?

[Sarah23]

I am thinking about getting an accessory flash in the next couple months...but I have NO idea what all the numbers and stuff means!

Can someone translate?

Is it possible to get one for around $50-$100? Or are those crap?

 

[Big Mike]

When it comes to flashes for modern cameras...there are a couple different ways to go.

Firstly there are 'dedicated' flash units. These will be the new/current models from the manufacturer (Canon)...and a few off-brand models. These flashes can communicate with the camera for metering. The flash fires a pre-flash which is measured by the camera, the camera then tells the flash how much light power will be needed and then the flash fires again. This is called E-TTL metering. This all happens quite fast, you probably won't notice that it fired twice. This means that you don't have to worry about setting the exposure or trying to figure out how to measure the light from the flash. The down side is that these are fairly expensive. I would suggest looking at the Canon 430EX.

You could get a cheaper flash unit, but you probably won't get E-TTL metering.

Some flash units have an auto sensor built into them. The measure the light themselves, but they don't communicate with the camera (only when to fire). HERE in an example, and HERE is another. With a flash like that, you would need to match the settings on the flash to the settings on the camera. It's not too hard to do (once you wrap your head around it) but you do have to be aware of it and change with your shooting conditions.

Lastly, you might find a manual flash that doesn't meter at all. It just fires at the power that it's set at (some don't even have power settings...just full power). You can still figure out how to use them because they will have a 'Guide number'. You just divide the guide number by the distance to the subject and that is your F number :er:

 

[solrac8126]

Sarah23
that's is a complete explanation from mike hehe
anyways let me give you a number translation of what i consider things you need to know. Mike already explained about E-TTL so here you have 3 more.

Guide Number
141 ft./43m (at ISO 100); flash head at 105mm zoom setting

this means the flash will "fill" with light up to 141 feet or 43 meters, using the ASA/ISO setting on your camera at 100 and the flash head to 105 millimeters which is also a setting on the flash.

Recycling Time
Approx. 0.1 to 3.7 seconds (AA-size Alkaline Batteries)/0.1 to 2 seconds (AA-size Ni-MH batteries)

This means the time the flash needs to charge again in order to flash (in this time you can't use the flash to fire the light)

AF Assist Beam

This will help you to focus when you have little or no light, it will light up with some leds the auto focus points you see in the camera in order to focus your subject.

 

[Socrates]

Guide Number
141 ft./43m (at ISO 100); flash head at 105mm zoom setting

this means the flash will "fill" with light up to 141 feet or 43 meters, using the ASA/ISO setting on your camera at 100 and the flash head to 105 millimeters which is also a setting on the flash.

The explanation is misleading as it ignores aperture.
f/stop = (GN X ISO)/Distance
Naturally, if GN is metric, the Distance must be metric.