Canon Speedlite Flashes Are Named After Their Guide Numbers

This is probably a “duh” fact for many of you, but one that some of you have perhaps never heard or realized before: Did you know that the flashes in the Canon Speedlite lineup are named after their maximum guide numbers? To figure out the power of your Speedlite, just take the model name and hack off the zero at the end to get the GN (e.g. 430EX has GN 43, 580EX has GN 58).

In case you’re not very familiar with the concept of guide numbers, Canon explains,

For those of you who aren’t fully au fait with guide numbers – the Guide Number (GN) is a measure of the power of a flashgun. The higher the GN, the more powerful the flashgun is. A guide number is found by multiplying the flash-to-subject distance by the aperture for a well-exposed photograph. For example, if good results are produced by using f/11 for a subject that’s 5 metres away, the guide number is 55. You need to know the film speed used, and that the distance was measured in metres, so guide numbers are usually written as ‘55 (ISO 100, metres)’.

It’s a naming system that makes a whole lotta sense, eh?

  • Bart Kuik

    What? You mean that there are brands that *don’t* name their flashes after their guide numbers?

  • peter25253

    yep and the 600EX is misleading because it only has a GN of 60 when zoomed to 200mm. otherwise it has the same power as the 580EX II

  • Luiz Fellipe Carneiro

    Yong Nuo for instance.

  • fuzzywuzzy

    This is one area where Canon really makes good over other brands: naming conventions that just make sense. Their bodies follow a pretty consistent and logical naming system as well (looking at only the numbers, not the stupid Rebel-this or Kiss-that).

    Contrast that with Nikon, who seem to name their products based on a weekly lottery.

  • Peter

    Same for Sony flashes

  • sierrarobba

    I want canon to make aps-c and full frame flashes separetly!Becaue i want ripp off newcomers!

  • AAnsel

    really? and did you know Nikon is a japanese firm?

  • David Jones

    no more misleading than any other flash. GN is actual light output focused with a reflector. If the reflector is more efficient (i.e. tighter beam, in this case), then the GN will go up.

    A 580EX has a higher GN at tight zoom and a lower GN at wide zoom. It is only misleading to those who don’t bother to know where they are going.