A high-quality flash is a must for almost every professional photographer.
The flash is a versatile tool for the professional photographer. While most people think of flashes as simply adding light when there isn't enough natural light, the purpose of a flash is often to introduce diffuse light and eliminate shadows. Canon's Speedlite line of flashes, previously including the 420Ex and the 580EX, is the choice of professionals that use Canon camera bodies. Choosing between the two simply requires an understanding of each flash's strengths.
Size
The Canon 420EX is a smaller flash than the 580EX. The dimensions of the 420EX are 2.8 by 4.8 by 3.9 inches, while the 580EX measures 3.0 by 5.3 by 4.5 inches. Despite the approximately 37 percent increase in volume, it is not likely you will notice the difference between the 420EX and 580EX in your camera bag.
Weight
Again, as the 580EX is a larger flash, it has a slightly higher weight. The 580EX weighs 13.2 ounces while the 420EX weights 10.6 ounces, both without batteries. Both flashes require 4 AA batteries, which will add about 3.5 ounces to the net weight. Again, the difference in weight is likely negligible if you are comparing the two flashes.
Guide Number
A flash's guide number describes the maximum distance the subject can be from the flash while staying appropriately lit. This allows for accurate comparison between different flashes, but shouldn't be interpreted as a real-world distance. The 420EX has a guide number of 138 feet at 105mm and ISO 100, while the 580EX has a guide number of 190 feet at the same settings. Obviously the 580EX is a more powerful flash.
Features
Both the Canon 580EX and the Canon 420EX fully support E-TTL metering and operation and are compatible with most recent EOS SLR cameras, both film and digital. Both flashes have heads that rotate fully for bounce flash use, and both can be wirelessly triggered using a Speedlite Transmitter. However, the 580EX adds support for an external power supply, which allows for faster shooting. Due to the 580EX's extra power, it uses more energy per flash, so the 420EX will provide more flashes on a single set of batteries.
Tags: guide number, Both flashes, Canon 420EX, guide number feet, number feet
