Hi, Kieran,
Hi
I have just bought a Vivitar 285hv as my external flash.
When I shoot with it on the hot foot it goes off, but the camera's exposure is determined as if there is no flash.
Is this usual and therefore do I need to exposure manually?
There is no cooperation between an EOS camera and a "non-dedicated" flash unit like the Vivitar 285HV. The camera doesn't even know that the flash unit is in place and active.
Thus you must set appropriate exposure parameters on the camera directly.
You may wish to set the shutter speed to something not faster than about 1/200 sec, so that proper X-sync behavior will be attained.
Then, regarding flash exposure, the 285HV offers automatic flash exposure control (via its own sensor). For this to operate properly, the camera aperture must be set to suit one of the three "color-coded" settings of the flash unit control dial. The needed aperture can be reckoned with the exposure calculator of the 285HV, based on the "color choice" and the ISO sensitivity to be used at the camera.
You can of course set the flash output to a predetermined fraction of maximum output. This can be handy when trying to properly balance the "ambient light" and "flash illumination" aspects of exposure.
