[James]

What do cheap external flashes lack that fancy speedlights have besides faster sync and wireless capabilities?

[Dabhand16]

If you are talking about Sigma and Cobra flashguns, although they will have modules that will dedicate them with whatever camera you are using, they might not support evey function that the camera's own brand ones will.

Best to check the specs to see if this is the case.

No doubt, someone who uses these flashguns will be along soon and will clarify it.

[James]

I meant the super cheap $20 Vivitars. And what functions are you referring to?

[Dabhand16]

Originally Posted by James

I meant the super cheap $20 Vivitars. And what functions are you referring to?

Hooking into the cameras metering and focus systems.

My Nikon SB-800 will zoom automatically when I zoom the lens, and can perform fill flash and other functions by integrating into the exposure system even if it is bounced or fired remotely.

[VinnyP]

The cheap ie non dedicated flashes don't communicate with the camera they just fire when the camera shoots. They usually have 2 modes, manual and automatic. In the first you can set the output and you have to work out the aperture etc based on the subject matter and the distances involved. In the latter you set an aperture (Based on ISO 100) and the flash uses it's own sensor to work out the correct flash output. The problem with this is that it's easily fooled and it doesn't take into account ambient light. Of course it's possible to allow for all of this and photographers have done for decades but on the whole a dedicated flash gives far more controlled results.