Help with off camera manual flash

caseysrt · Jul 14, 2012

I have a D3100 so no commander mode, and an SB700 flash. I almost always use natural light but would like to start using the speedlight.

I have to use the flash in full manual mode (using wireless triggers) but I either underexpose or overexpose the image, when I am in manual mode is zoom and power the only things I have control over?

Let's say I'm at f4 at 160/sec and ISO 200 and I want a wide spread of light, I would zoom out to help spread the light, but what would I set the power to? Is it just trial and error?

tirediron · Jul 14, 2012

What you really need is a flash meter, but failing that, you can work out exposure via the guide number (GN). Head over to the Strobist Blog (The #1 resource for off-camera flash work) and read this page about using the GN to calculate exposure. It's very easy when you get the hang of it.

oneguywithacamera · Jul 24, 2012

If you're at f4 at 160/sec and ISO 200 - flash on full 1/1 power there a couple of things you can try. First, and assuming your camera is in manual mode with manual ISO set, take a shot - then either ride the aperture or ISO up or down. The shutter speed, as long as it's below your sync speed, will only effect the ambient light of the exposure, not the flash. Take another shot. It should be either darker or lighter depending on how you adjusted it. Continue to try this until you get your exposure down. Say you end up with a correct exposure at f8 at 160/sec and ISO 200 - your flash still on full 1/1 power. f8 is 2 stops darker than f4, so if you'd want to go back to your original exposure at f4 you'd need to take 2 stops (-2 EV) out of the flash or set the flash to 1/4 power. Hope that helps.

cgipson1 · Jul 24, 2012

Don't forget you can also adjust the power on the flash (as mentioned). This will allow you to control what aperture you use to shoot with (to help control the background). If you are just wanting fill from the flash.. set it to low power 1/128 or so, and play with it. Learn the approximate distance and where you can place it from the subject to get the fill exposure you want. Once you do that for a while, it becomes second nature, you don't even have to think about it.