New to flash photography. low light situation and my flash is on light stand. When I click on aperture mode with low iso the shutter speed is very slow. And if I increase the iso the shutter speed gets better as expected. But the problem is since Im using flash the eventual photo is over exposed. The problem is camera thinks that the flash is not on (off camera manual) and therefore assumes that its clicking without flash but the reality is that flas does gets triggered. Am I missing some setting?