Shooting with One Off camera Speedlight, plus the Popup

OnTheCoast · Jun 7, 2012

I have been using my hotshoe vivitar 383 in TTL function with much success, but I would now like to put the Vivitar on a stand and use it as a main light along with the cameras popup flash as fill, and also to fire the Vivitar,

however since the flash is no longer on the hotshoe the TTL function is gone I imagine, But while still being in TTL the popup flash is now going to try and compensate and act as the main exp. source! So my question is, how can I now figure the exposure for the vivitar Speedlight as the main and the popup as Fill while still using it to fire the Vivitar on the Light stand?

Thanks Jon

Infidel · Jun 7, 2012

Don't use ttl; so long as you're using OCF, you may as well determine all of the exposure settings and ratios manually.

OnTheCoast · Jun 7, 2012

Infidel said:
Don't use ttl; so long as you're using OCF, you may as well determine all of the exposure settings and ratios manually.

I understand in manual mode changing shutter speed and lens opening to determine correct exposure, but how do you ajust the lighting ratios ...only by moving the lights distance's correct!

Infidel · Jun 8, 2012

Speed lights themselves have manual settings, essentially in terms of stops (1/1, 1/2, 1/4, 1/8, 1/16, 1/32, etc) relative to full power, which is of course, 1/1. Otherwise, your instinct to vary distance is both correct and insightful. Useful passage from here: Inverse-square law - Wikipedia, the free encyclopedia

In photography and theatrical lighting, the inverse-square law is used to determine the "fall off" or the difference in illumination on a subject as it moves closer to or further from the light source. For quick approximations, it is enough to remember that doubling the distance reduces illumination to one quarter;[4] or similarly, to halve the illumination increase the distance by a factor of 1.4 (the square root of 2), and to double illumination, reduce the distance to 0.7 (square root of 1/2). When the illuminant is not a point source, the inverse square rule is often still a useful approximation; when the size of the light source is less than one-fifth of the distance to the subject, the calculation error is less than 1%.

Infidel · Jun 8, 2012

Also, with the camera in manual mode, changing shutter speed ONLY alters ambient exposure, whereas aperture and ISO influence ambient and flash exposure. Read the "Lighting 101" article on the strobist blog (google it). This is because the flash duration is essentially always shorter than the fastest flash sync shutter speed that your camera can manage...the entirety of the flash occurs within time the shutter is open.