I am about to embark on 'Dog Photography' having previously done mainly landscapes and wildlife. I want to work in peoples' own homes with portable lighting. I have purchased a Lastolite softbox and a black/white vinyl backdrop. I have a Sony α900 camera and mainly use a Zeiss 24 - 70 mm lens. My flash is a Sony HLV-F36AM, with a remote speedlight trigger (PT series) which I bought on eBay. But it doesn't appear to be strong enough, as I have to have a shutter speed of about 1/200, ISO 400 and f/5.6 on the black background. I have tried using the Manfrotto Spectra LED 500S on the opposite side to the softbox which helps a bit but it's all hit and miss especially as dogs move!
Can you tell me how powerful/what type of flash unit would best suit my needs? I didn't really want the expense of another Sony if possible, as my project may not take off enough to pay for itself. I looked at a Nissin on Youtube which looked good but having read lots of your forums I'm not sure now. What do you think?