Sekonic L-358 & Lighting Ratio Calculation

Hi All,

I have a 580EX II and a 580EX which I want to use for fill light (580EX II, Master) and key light (580EX, Slave) to get a lighting ratio of 1:3. I'm new to using a flash meter to determine correct exposure, so I need some help here.

The lighting ratio instructions (page 23 of the manual) for my Sekonic L-358 are for a continual light source. I would assume the steps would be the same for flash except that the meter is set for Auto Reset Cordless Flash Mode.

OK, so I follow the instructions on page 23 and with a shutter speed of 1/125 I too get a difference in EV of -2, giving me a final lighting ratio of 1:3.

Do I now raise the Lumisphere, point it to the camera, and then trip both flashes together to get the desired f-stop value? Is there a different, perhaps easier or more efficient approach I should take with determining flash exposure with this setup?

Thanks,
~Dom

If you are operating the Speedlites in ETTL mode (where the camera and Speedlites work out the exposure control automatically), it makes no sense whatsoever to even try to use the handheld light meter. That's because the pre-flash from the Speedlites will be seen by the meter and the main flash will then be totally ignored. On top of that, you have absolutely no real control of the main flash levels other than setting the flash exposure control (FEC)value.

If you operate the Speedlites AND the camera in full manual mode, then you can use a meter and adjust the camera's f-stop & ISO values to achieve the correct flash exposure. The shutter speed lets you combine ambient light in the exposure. If you don't understand this, we can go deeper.

The L-358 can show you the ratio of ambient (constant) light and light from the flash source(s) as you have read in the owner's manual. If you want to measure and adjust the difference between 2 or more flash units, though, you will have to read each flash source independently and adjust each (by setting power level or position) for the desired results. The meter cannot tell you the difference between two flash source levels with a single reading.

Hi Skip, yes I will be using the flash units and camera on manual. I think I understand the steps to determine the flash ratio and final (total) exposure. In a studio setting (my garage) what should I aim to have as the % flash versus ambient setting?

Thanks,
~Dom

Obtong wrote in post #7923190
Hi Skip, yes I will be using the flash units and camera on manual. I think I understand the steps to determine the flash ratio and final (total) exposure. In a studio setting (my garage) what should I aim to have as the % flash versus ambient setting?

Dom, that fully depends on what you want the images to look like.

If you really want to have total control of the lighting, you should use the fastest shutter speed you can get away with (the "max sync speed" or slightly slower). That would make the ambient light essentially non-effective. Typically, this is the way folks work in a studio situation. With only two flash units, you'll probably want some movable reflector panels to fill in shadows.

If you need to have the ambient light for the background, then you need to try various ambient/flash ratios - controllable with shutter speed after finding a suitable aperture/ISO for the flash setup.

If you're going to mix ambient and flash lighting, you should get appropriate colored gels to go over the flash unit(s) to change the light color from the flash unit(s) to closely match the color of the ambient lighting. A "CTO" gel (a special orange) is typical to make the flash output appear about the same as incandescent lighting.

I'm just learning how to shoot with strobes... but I do what Skip talks about above. I use 1/200th on my 40D to kill what little ambient light there is in my basement studio. (Slightly less than x-sync b/c I get a very small black band from the shutter if I don't... anyways.) Therefore, the only light that's going to affect my image is from my strobes, and I have total control over the ratios.

From there, I just take readings with the lumisphere down on my L-358 (cordless flash mode) pointed at each strobe to get the ratio where I want. You can use the Delta Ev function to find the ratio, but I usually just do it in my head b/c I think in f-stops and not Ev's. Finally, lumisphere up and toward the camera to determine the appropriate f-stop for the image.

A site with videos, tutorials, and setups that has helped me a lot is http://www.studiolight​ing.net . YouTube also has some good lighting tutorials (I like the "Digital Photography 1 on 1" series).

Remember that the lighting ratio is Key + fill : fill not key : fill.

Really? I thought it was a ratio between each of the lights individually (key:fill) (key:background) etc? That was the way it was explained to me. Do you have to measure lighting ratios differently depending on what effect you're going for?

The key light refers to the most dominant source of light, the light you are basing your exposer off of.

Mike V wrote in post #7925871
Remember that the lighting ratio is Key + fill : fill not key : fill.

Yes, the term 'lighting ratio' is so often mistakenly used in the context of "relative intensity ratio of 'main intensity:fill intensity' "

If Main provided 2 parts of light to one side of face, and Fill provided 1 part of light to full face, the 'lighting ratio' is 3:1 even while the Key:Fill ratio is 2:1

If this sounds confusing, remember that from the camera's point of view, the main light illuminates part of the subject, but the fill light illuminates the shadows and adds its light to the part that is illuminated by the main light.

The highlight areas get light from both lights, the shadows get light only from the fill light.

Wilt wrote in post #7932257
Yes, the term 'lighting ratio' is so often mistakenly used in the context of "relative intensity ratio of 'main intensity:fill intensity' "

If Main provided 2 parts of light to one side of face, and Fill provided 1 part of light to full face, the 'lighting ratio' is 3:1 even while the Key:Fill ratio is 2:1

These are just the first three that came out in google


http://en.wikipedia.or​g/wiki/Lighting_ratio

Lighting ratio in photography refers to the comparison of key light (the main source of light from which shadows fall) to the fill light (the light that fills in the shadow areas). ...A keylight of 800 footcandles and a fill light of 200 footcandles has a ratio of 4:1...

http://www.vividlight.​com/articles/1916.htm

Now, what is the ratio? In a nutshell, the ratio is the difference between the main light and the fill. If your main light were twice as bright as your fill, the ratio would be 2:1. Thinking about exposure factors, a factor of 2 is equal to one stop of exposure, and if you increase your exposure by one stop, you are allowing in twice the amount of light.
Therefore, a 2:1 ratio would mean that there is a one-stop difference between the lights. A 3:1 ratio would be a stop and a half difference, and 4:1 would be a two-stop difference.

http://www.cybercolleg​e.com/tvp033.htm

This key-to-fill brightness difference is expressed in terms of a lighting ratio.

Gosh... That's a lot of info!

Doesn't the 580EX and EXii emit a preflash, even in Manual mode? How will that affect flash metering?

~Dom

Obtong wrote in post #7933726
Gosh... That's a lot of info!

Doesn't the 580EX and EXii emit a preflash, even in Manual mode? How will that affect flash metering?

~Dom

The Speedlites, when used in manual mode, do not emit a pre-flash. You can use a handheld meter to analyse their output when the flash units are in manual mode but not when they are used in ETTL modes.

SkipD wrote in post #7933758
The Speedlites, when used in manual mode, do not emit a pre-flash. You can use a handheld meter to analyse their output when the flash units are in manual mode but not when they are used in ETTL modes.

Thanks Skip. What I have found is that when I take a flash meter reading by pressing the Master's Test button, I get a reading of 1/125 f6.7 @ ISO 200. If I meter by actually taking a picture, the meter reads that there is enough light.

I suspect that when taking a picture, the preflash is fired, even if the flash is in manual mode, so users should only meter the manual 580EX flash output by pressing the Test button.

~Dom

If the flash is in manual wireless mode does it emit a pre-flash? I thought it did. Isn't that how the slaves power is adjusted?