Strobe Lighting

scottphotography · September 10, 2008

After I set my exposure on the camera, say f8, what setting to I put into the strobe lights (2) if I want a 1x2 or 1x4 ratio? What number do I start w/that correlates to my exposure? I have Elinchrome 400's w/digital readouts on back.

Thanks.

LiquidAir · September 10, 2008

scottphotography wrote:

After I set my exposure on the camera, say f8, what setting to I put into the strobe lights (2) if I want a 1x2 or 1x4 ratio? What number do I start w/that correlates to my exposure? I have Elinchrome 400's w/digital readouts on back.

Thanks.

It entirely depends on how you have set up your lights. The simple way to answer these questions is with a light meter. Get a good Sekonic and you'll be set.

scottphotography · September 10, 2008

LiquidAir wrote:

It entirely depends on how you have set up your lights. The simple way to answer these questions is with a light meter. Get a good Sekonic and you'll be set.

So r u saying the meter will tell me what number to set my lights to? I thought it only told me the f/stop to set the camera to?

ChatKat · September 10, 2008

Camera's Synch Speed

scottphotography wrote:

So r u saying the meter will tell me what number to set my lights to? I thought it only told me the f/stop to set the camera to?

You camera has a synch speed. For using strobes, you set your camera on Manual. Your ideal shutter speed depends on the camera but usually 125 to 250 is the normal range. The lightmeter will tell you what aperture to use. You may need to read more than one part of the scene and average it. You can also use your histogram to check exposure.

LiquidAir · September 11, 2008

scottphotography wrote:

So r u saying the meter will tell me what number to set my lights to? I thought it only told me the f/stop to set the camera to?

Give or take, here's how I work:

Let's say I want to take a portrait at f/8 with a 2:1 ratio. That means I want my fill light 1 stop underexposed. Here's the process:

First I set up my fill light and set the power to 1/4. I measure the fill light with my meter. Say it comes out to f/11. Since I want my fill light underexposed by one stop, that means I want it to measure f/5.6 so I turn the power down by two stops to 1/16. Once I adjust the power, I check with the meter to make sure that I actually hit f/5.6.

Now I set up my main light to one stop brighter than my fill, or 1/8. I turn on BOTH strobes and measure the combined output with the meter. Lets say the measurement comes out to f/10; that means I am 2/3 stop too hot so I turn the power on the main down by 2/3 stop and measure again. Since I am measuring the combined power of all my lights the relationship between main power and meter is not simple so often it takes a few tweaks of my main light to hit my overall meter target of f/8.

This is the most consistant and accurate way I know of to set up lights. In practice I have a little black book full of each lighting setup I use which includes a sample print, a lighting diagram, and all the power settings. I still check it with the meter, but if I am working from my book my initial setup is going to be quite close and only need small adjustments. If I am trying a new setup, I usually can find something close in my book for my initial power settings and, of course, I make sure that record the new setup in my book once I have it tuned.

Llywellyn · September 11, 2008

LiquidAir wrote:

Give or take, here's how I work:

Just...wow.

This totally amazes me. I understand the steps, but I don't understand the calculations at this point in my experience. How you would know that a one-stop underexposure on the fill meant metering to f/5.6 instead of f/11 blows my mind. I already admire you and your work immensely, but this brings my respect for you to a whole new level.

pathfinder · September 11, 2008

If the fill light is correctly exposed at f5.6, then when shot at f8, the fill WILL BE 1 stop darker than the main light, which is going to shoot at f8 correctly.

Scott_Quier · September 12, 2008

I do it slightly different from the way described by LiquidAir:

Decide on the desired ISO and the approximate aperture - just to keep things the same as LA's example, let's assume f/8. Shutter speed is not really material as long as it's fast enough, for the selected ISO and aperture, to exclude ambient light as an exposure contributor - unless you want to balance ambient with strobe (and then you have a slightly more complex problem to solve).
Decide on the lighting ratio desired.
- 1:1 Kinda boring
- 1:2 is nice for most portraits, especially of the young and ladies, corporate headshots (our choice for this example, again, just to be consistant with LA). This is the fill is 1 stop less then the main (or 1/2 the power, that's where the "2" comes from!:D).
- 1:3 Getting a little strong for ladies, works well for most guys
- 1:4 and steeper can work nicely for guys and/or for low-key shots. Can you guess. The main is a full 2 stops (4 times) brighter than the fill.
Set power on the main light
- Gotta start somewhere, 1/4 power is a nice place to start
- Meter it. Is it close to your desired aperture, maybe just a touch under? Yes -> good. No -> adjust the power and repeat this step
- Turn off the main light
Set power on the fill
- f/5.6 is one stop less light than f/8 so let's look at the power setting on the main light. Subtract one stop from that and dial that into the fill.
- Now look at the relative main-subject and fill-subject distances. If the fill is closer, then we need to dial down the fill a touch. If it's further from the subject, dial it up just a touch
- Meter it. Is it close to your desired aperture, maybe just a touch under? Yes -> good. No -> adjust the power and repeat this step
Turn on the main light again
Meter the total light at the subject. If our "just a touch under" was the right amount, our meter reading will be really close to the desired f/8 and our lighting ratio will be spot on.
Set your camera and take a shot. Study the histogram. Is the exposure right? Look at the picture in the LCD - are you absent of any blinkies? The answer to both questions should be a resounding "Yes!" Because this is digital and digital images look best if "shot to the right", I might open up the aperture 1/2 stop just for the histogram shift and then correct it in post processing. Look here for more information on why exposing to the right is usually a good idea.

As for the "calculation" - this is a simple matter of remembering.... The "stops" go in this squence:

1, 1.4, 2.0, 2.8. 4.0, 5.6, 8.0, 11.0, 16.0, 22.0, 32.0 ...

The jump from one number to the next is 1 stop. A meter reading indicating f/2 is twice as bright (1 stop brigher) than a meter reading of f/1.4.

pathfinder · September 12, 2008

When talking about f stops, it is good to remember that f8, when set on a lens, is the size of the aperture that admits light ( and allows 1/2 half the amount of light admitted by f5.6), but when talking abut strobes, the amount of light that is correct for f8 is twice as bright as the amount of light that is correct for f5.6.

If you recall and understand that aperture controls the amount of light from a flash ( independent from shutter speed which in the studio range of 1/60th to 1/250 plays no significant role in exposure since ambient light is so much lower than the flash lighting ) then the first statement makes sense - but otherwise sounds like gibberish:D

Great discussion Scott and LA. I always have trouble recalling if the ratio is between main and fill, or between total light ( main + fill ) and fill. I am still a little confused about that.

LiquidAir · September 12, 2008

pathfinder wrote:

Great discussion Scott and LA. I always have trouble recalling if the ratio is between main and fill, or between total light ( main + fill ) and fill. I am still a little confused about that.

As far as I can tell, there is no consistency in the industry about that. I think many people use that ratio to refer to the ratio between main light and fill light power. If you are using something akin to the classic mall portrait setup with a pack, a strobe left and right and an umbrella on each then main to fill power is as simple as dialing it in on the pack.

However, I generally use asymmetric lighting where the main and fill are placed at different distances with different modifiers so the ratio between the power on my strobes doesn't correspond to the ratio of light on my subject. Because of that, my preference is use the ratio between my fill light and the overall exposure for a few reasons: it tells me exactly how deep the shadows will be (which is important for print where the dynamic range is less than in the camera), it generalizes well to more exotic lighting scenarios with more that two subject lights, and its easier to reproduce my studio lighting in situations where I am using ambient fill rather than a dedicated fill light.

pathfinder · September 12, 2008

LiquidAir wrote:

As far as I can tell, there is no consistency in the industry about that. I think many people use that ratio to refer to the ratio between main light and fill light power. If you are using something akin to the classic mall portrait setup with a pack, a strobe left and right and an umbrella on each then main to fill power is as simple as dialing it in on the pack.

However, I generally use asymmetric lighting where the main and fill are placed at different distances with different modifiers so the ratio between the power on my strobes doesn't correspond to the ratio of light on my subject. Because of that, my preference is use the ratio between my fill light and the overall exposure for a few reasons: it tells me exactly how deep the shadows will be (which is important for print where the dynamic range is less than in the camera), it generalizes well to more exotic lighting scenarios with more that two subject lights, and its easier to reproduce my studio lighting in situations where I am using ambient fill rather than a dedicated fill light.

Maybe that is why I seem to be confused at times.

I can see that using a meter to meter flash, and ambient, separately, can be a big help for on location portraits, where you are not using multiple strobes, ala Strobist.

The ability to separately control subject, and background lighting, like a stage director in a theatre offers very powerful tools to a shooter.

LiquidAir · September 12, 2008

pathfinder wrote:

I can see that using a meter to meter flash, and ambient, separately, can be a big help for on location portraits, where you are not using multiple strobes, ala Strobist.

Ya. My meter computes the flash, ambient and combined exposure all in one shot. I get 3 little tick marks on a graph.

The ability to separately control subject, and background lighting, like a stage director in a theatre offers very powerful tools to a shooter.

That is often the challenge of studio work. It takes either a lot of space, careful control with grids, flags and gobos or some combination of the two.

pathfinder · September 12, 2008

Discussion of lighting out of the studio, made me think of this recent thread about that subject

Strobe Lighting

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