Ask Matthew…
Q I’ve noticed that Nikon’s various Speedlight flashguns have different power ratings or ‘Guide numbers’ but how do these work out in practice?
Gavin Yates
The Guide number (Gn) of a flashgun is a measure of its maximum output. The larger the number, the greater the maximum intensity of the flash. The Gn is usually specified in metres at an ISO rating of 100. It’s also
