hi, i just want to seek some opinions about flash photography.
i am using a yongnuo yn460ii flash unit which is rated at 38m @ ISO 100 and 53m @ ISO 200. i just wanna know whether the guide number will increase when i increase the ISO?
i read from:
Doubling of film speed will increase the guide number by a factor of 1.4 . Going from ISO 100 to ISO 400 film, the guide number is doubled. Going from ISO 100 to ISO 25, the guide number is halved.
i understand that @ ISO 400 the GN is effectively doubled(1.4 x 1.4). so i went to do some calculation and realised that if i am to shoot at ISO 3200 with my flash, the GN will be 203.6m. so, using the formula GN = distance x f-stop, ie @ F8 the flash will be covering a distance of 25.5m.
i feel that the figures are a bit imba and i am really skeptical as to whether the flash can reach out over 25m, so can anyone share your experiences? and if i were to bounce flash(from bounce card, ceiling etc), then how would the calculation be again?