Flash Technique

ian408 · November 28, 2010

Hola!

I'm trying to work on flash technique. In particular, using flash in daylight conditions to emphasize parts of a photograph.

Here, I tried to underexpose the BG by shooting manual mode and then using ETTL on the flash to compensate. I used only a single flash on a cord plus a Stofen to soften the light.

I think to improve the shot, I need to do a few things. Light the rear of the bike, light the back to mitigate the shadows. Is my thinking correct? Are there other things I need to be aware of/try?

edit: adding one more.

Icebear · November 28, 2010

Ian, I don't think a Stofen does a thing for you outdoors, except waste most of your light. You need walls and ceilings for the stofen to do anything for you . . . I'm purdy sure.

ian408 · November 28, 2010

Icebear wrote: »

Ian, I don't think a Stofen does a thing for you outdoors, except waste most of your light. You need walls and ceilings for the stofen to do anything for you . . . I'm purdy sure.

You're right. I tried with/without.

pathfinder · November 28, 2010

Ian, what you are wanting to do is two separate exposures in one shutter movement.

You are lighting the bike with the flash with the camera in Manual mode, the flash in ETTL. Your exposure of the bike is a function of ISO, and aperture and flash output. You use the manual settings in the camera to control the background exposure, with shutter speed being a significant part of your control... You MAY need to turn on High Speed Synch out of doors in bright sunlight to allow your shutter speed to be short enough to under exposure the background one stop or so.

One way to approach this is to determine the correct exposure for the background. From the Sunny 16 rule we know that at ISO 100, the correct exposure for a sunlit background is f16 and 1/ISO for a shutter speed, or ISO 100. F11- 1/20th, or f8 1/400th ( but your max flash synch shutter speed is 1/200 or thereabouts ). To under-expose the background 1 stop, then we need f8, 1/800th for ISO 100 and a sunlit background.

So plug f8, ISO 100, 1/800th into your camera in Manual Mode. Turn your EOS flash on with High Speed Synch enabled, and no Flash Exposure compensation. Your camera will under expose the scene by 1 stop, and your flash will adjust the exposure via ETTL to properly expose that near subject. One limit you must deal with is the limited amount of light available from your speedlight. It will HAVE to be closer than 4 f-5 feet or so in bright sunlight or you will run out of enough light. Syl Arena has ganged as many as 16 speedlights to overdrive sulight at times. This is one reason this techniques is easier to do at dusk or on an over cast day.

I published a power table for a 285HV here and this will give you a general idea of how close your speed light needs to be to overdrive direct sunlight.

Here is a post with power outputs for a 550ex which is close to the power of a 580ex. The power limits of speedlight ultimately come down to the power in 4 AA batteries, and a capacitor that can be charged at 6 volts. I have several shots of plastic horses lit with strobes in sunlight in this gallery http://pathfinder.smugmug.com/Landscapes/Horsin-Around-in-Terre-Haute/3193011_e2zLW#177100600_BjppL You will have to check the exif data for whether flash was used, although if you look carefully you can identify some of them by eye also. Some of these were done with a speedlight in a 24 x 24 inch softbox, so a although a Stofen just wastes light for you out of doors, if you can get your flash close enough it will work.

This is a great technique for macro shooting as well, as you can drive sunlit backgrounds to black once you overdrive sunlight by 3-4 stops, which at macro distances is very easy with a speed light only 6-12 inches from a subject.

ian408 · November 28, 2010

Hi Jim. Thanks for the links and charts and stuff. But I'm still wondering if I'm on the right track with my pix?

pathfinder · November 28, 2010

It sounds like you are wanting to do more extensive painting with light, which really means setting up several off camera flashes and co-ordinating their exposures not via ETTL but entirely manual strobe adjustments, and triggered with PWs or their equivalents.

Yes you could paint the bike with flash from both sides, and behind as well, 1 stop brighter than the sunlit background. Takes a bit longer to set up, but will separate your bike from the background even more strongly. You may need stands, booms, flags, or diffusers as well. Or flash from one side and a reflector opposite it.

r3t1awr3yd · November 29, 2010

I must be thinking backwards but what I would do...

Adjust the aperture/shutter speed/iso for the background exposure you want and add light to where you want AFTER you've got that sorted out and aren't going to move the camera (tripod) or the object you want to light.
THEN
Add flash to wherever you want and chimp adjusting the light level of the flash (on manual) as you see fit.

EDIT: I just read the post above mine. Okay, I'm not thinking backwards lol.

Flash Technique

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