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2 lamps. What apperture on the camera?


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<p>Hi !<br>

I shoot a lot with one lamp. That's simple enough, I measure the the light and try to get an aperture of 8 on the camera for example. <br>

But what if I want to have another lamp on as well, to make the light a little more interesting?<br>

Let's say I want lamp number two to measure aperture 4 on the camera. <br>

What should the camera then be on? Still 8? Or something in between?<br>

Thanks.</p>

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<p>Do you flash or continuous hot lamps? Either case since you have the meter simply meter with both lights on. Most likely the aperture would still be 8 or slightly smaller like 9 or 10. It's depend on how you position the lamps. If both at the same place pointing at the subject the aperture would be between 9 and 10. If the 2 lamps are of opposite angles like one is for fill than the aperture is still 8. But if you use the meter it will tell you. </p>
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<p>Although theoretically you can calculate this sort of thing (and I have created an Excel spreadsheet that tries!), <em>reasonably</em> accurate calculations are fairly complex, and no calculations are likely to be highly accurate. Real-world answer: buy a meter, even a basic flash and incident meter like a Sekonic 308 will do fine. Or else experiment.</p>

<p>Most basic answer: what BeBu said; if two lamps are lighting the same area, one alone would call for f/8, and the other alone would call for f/4, then you have 1.25x as much light as needed for f/8, so you need just about f/9.</p>

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<p>Light is additive. Meaning if you've got two lights of equal strength pointing at the same part of the subject you'll have twice as much light, i.e. +1 stop. However, if the lights don't overlap (say you light one side of a person's face with one light and the other side with the other light) then the light doesn't add and the exposure stays the same as with one light. BTW, I don't recommend that style of lighting!</p>

<p>Short answer. Get yourself a meter and save yourself the brain ache. An incident reading taken from the subject position pointing back at the camera is almost infallible.</p>

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<p>Hi Sarah,<br>

First to answer your aperture question:</p>

<p>Main alone reads f/4 - add second light doubling the light on the subject, aperture change is 1/f stop bust in light thus you must close down to f/5.6.<br>

The f stops in order from brightest is: 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 -11 -22 - 32<br>

Math is only lamp reading times 1.4 ( 4 x 1.4 = 5.6). This assumes both play on the subject with equal intensity. If you were to install three equal lights, the multiplier becomes 2 (4x2=8 use f/8). These seemingly odd multipliers are due to the fact that the lens and aperture are circles so we must use geometry of circles to solve.</p>

<p>As to using a multiple light setup:</p>

<p>You would be wise to experimented using multiple lights. Typically a single main light is set high and off to the side. This location imitate afternoon sun. Now the one-lamp setup is likely to yields images that are too contrasy ((shadows too dark and void of detail). We can see detail in the shadows because our eyes automatically adjust but the camera likely cannot record detail in the shadows.</p>

<p>There are many ways to soften the shadows cast by the main lamp. This is the stuff of reflectors or soft-boxes and the like. In the studio, however we can add another lamp called a fill. We use the fill to mitigate shadows that record too deep.</p>

<p>Best if we fill shadows from the cameras viewpoint. To accomplish we place to place the fill lamp at camera height close to a line drawn camera to subject (position of main and fill not engraved in stone). Generally, the fill light is set to play on the subject with reduced intensity as compared to the main. This establishes a one light illusion that many admire. We adjust the intensity of the lamps by moving them closer or further away from the subject or by a setting on the light fixture.</p>

<p>We can use the fill brightness to adjust the contrast of our picture. If the main and fill both play equally the results are said to be flat lighting (low contrast) and thus uninteresting. A tried and true setup adjusts the fill so that its light arrives at the subject plane at half power as compared to the main. We call this difference in intensity the lighting ratio. If both are set to deliver equal light, the ratio is 2:1 (flat). In this setup, the main delivers say 100 units of light and the fill delivers 100 units. Surfaces that receive light from both thus get 200 units however; the shadows will only receive light from the fill and this is 100 units. The ratio is 200:100 which reduces to 2:1.</p>

<p>Consider a classic lighting whereby the fill is set subordinate to the main by 50%. This setup preserves the illusion of one light. Important because most times, multiple lights produce multiple shadows and thus distract.</p>

<p>We meter to get the desired ratio. With only the main on, meter the scene and note the aperture setting. Now turn off the main, turn on only the fill and meter again. Now adjust fill brightness to achieve a reading that requires you to open up the lens one stop. Example: main only reads f/8 then set the fill only reads f/5.6. A one-stop difference sets the ratio at 3:1. In this setup, the main delivers 100 units, the fill 50 units. The frontal areas receive both so the highlight areas get 150 units. The shadow areas receive only 50 units. The ratio is 150:50 and this ratio reduces to 3:1. The 3:1 ratio is call the "bread and butter" ratio because it sells best.</p>

<p>If you experiment with different lighting ratios, you can better understand the effects.</p>

<p>Main and fill equal yields flat lighting 2:1 ratio (flat)<br>

Fill set 1stop subordinate yields 3:1 ratio (bread and butter)<br>

Fill set 2 stops subordinate 5:1 ratio (zippier with more contrast<br>

Fill set 3 stops subordinate 9:1 ratio (theatrical high contrast)</p>

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