Help me with Lighting Ratios!

[aleks_biteman]

<p>Ok, so, today I had a competition at my high school, and I know I didn't do very well on the studio lighting section. I want to explain to setup. and requirements:<br>

2 light setup<br />Light Meter<br>

Style: Rembrant <br />Ratio: 4:1</p>

<p>So, if your camera is at F/8 ISO 100 1/60, you sync the Main/Key light up to read F/8 on the light meter. Then shouldn't you set the Fill to read F/16? Considering a ratio of 1:1 is even, 2:1 is 1 stop difference, 4:1 is a 2 stop difference, so that's what I did. And the images seemed flat, and I was getting almost a 1:1 ratio. You could hardly tell it was Rembrant because there was no "triangle". What did I do wrong? Thought I had this in the bag because I studied... well crap haha. I'd love to understand this better, only if there was a redo on the competition!</p>

[Matt Laur]

<p>If you set your fill light to be brighter (f/16) than your key (at only f/8), you're definitely going to fill in your shadows and make things look flat. In essence, you have your f-stops backwards.</p>

[aleks_biteman]

<p>well that'd do it! derp, amateur move haha. Totally had my logic backwards! Thanks you!</p>

 

[Alan Marcus]

<p>I am a photo engineer not a photographer. In my youth I was a teacher at the Professional Photographers of America School for continuing education. My subject was color print and process. However, I often monitored and helped some of the best rated portrait photographers in their classroom. Some ideas and thoughts may have rubbed off! <br /> <br /> Some tips on portraiture and lighting: <br /> <br /> As to portrait lighting:<br /> <br /> Our media is for the most part 2 dimensional reproductions of 3 dimensional objects. Our lighting should give an illusion of depth. The shadows give this illusion. The shadows must not be too dark because if too deep, they will be void of detail.</p>

<p>We start with a two-lamp set-up: a main and a fill. The Rembrandt setup presents an illusion that the subject is illuminated by just one light source that emanates from above. Actually, this simulates afternoon sunlight. The fill is set at lens height as close as possible to an imaginary line, lens-to-subject. Remember we fill shadows from the camera's viewpoint, not the viewpoint of an observer near the camera. <br /> <br /> <br /> Consider a portrait 2:1 (Flat Lighting): We place the main high and off to the side causing it to shine down on the subject. Let us say the main delivers 1000 units (watts if you like) on the subject. The fill is placed near the imaginary line at lens height and adjusted to deliver light to arrive at the subject plane with equal light energy as the main. Thus the main and the fill each contribute 1000 units of light. Now the frontal part of the face receives light from both. Thus, the total on the frontal areas of the face will be 2000 units because the light from the main and fill are additive.<br /> <br /> <br /> Now some areas of the face are in shadow. These are locations where the main could not reach; we are talking about dimples and valleys and nose shadow etc. Consider the circumstances: 2000 units on the frontal areas and 1000 units in shadow areas. Mathematically this can be stated as a ratio. The ration is written as 2000:1000. This is handled like a fraction that can be reduced by dividing both sides by same number. The reduced ratio is written as 2:1. This 2:1 lighting ratio is flat nearly featureless. <br /> <br /> <br /> Now consider a portrait set-up 3:1 ratio (bread and butter lighting). This one wins contests and sells best. To achieve we reduce the fill energy at the subject plane to half power as compared to the main (1 f/stop or 50% less energy at the subject plane as compared to the main). We might do this by setting, a knob on the fill lamp or we can just move the fill fixture further away from the subject. <br /> <br /> We can calculate a 1 f/stop difference, fill-to-subject (assumes both main and fill are identical). We measure main-to-subject distance and multiply this value by 1.4. The answer is a revised fill to subject distance. This added distance reduces the light energy playing on the subject by 50% (1 f/stop). The 1.4 factor is derived from a law in physics known as the inverse square law. The idea is to cause the main to deliver 1000 units and the fill 500 units. Now consider the frontal area of the face gets light from both fixtures. The values are 1000 main + 500 fill. Thus the frontal areas receive 1000 + 500 or 1500 units. Shadows receive only the fill’s 500. Ratio is 150:50 reduces to 3:1. This is achieved if the fill is subordinate to the main by 1 f/stop. You can also place main and fill using a meter. The trick is again 1 f/stop difference, fill subordinate. This is the Rembrandt setup. <br /> <br /> Consider 5:1 somewhat more zippy lighting. <br /> <br /> We reduce the fill to 1/4 power by knob on the unit if available or by setting the fill even further back. If the fill is at the 2:1 distance (same distance as main), we multiply by fill-to-subject distance times 2. If the fill is positioned at the 3:1 distance, multiply fill-to-subject distant by 1.4. You are after a two-stop difference with the fill subordinate to the main. How is this 5:1? This placement causes the fill to be 2 f/stops subordinate or 25% of the main’s energy. Now the frontal area receives 1000 from the main and 250 from the fill for a total of 1250 frontal and 250 in the shadows. The ratio is 1250:250 or 5:1. This is contrasty lighting. <br /> <br /> Consider 9:1 somewhat theatrical, very zippy lighting. <br /> <br /> If we reduce the fill to 1/8 power by knob or measurement 3 f/stops subordinate to the main. From the 2:1 position, the multiplier is 2.8 from the 3:1 position the multiplier 2, from the 5:1 position the multiplier is 1.4. Main continues to delivers 1000 units the fill 125 units. Thus the frontal areas receive 1125, the shadows 125. The ratio is 1125:125 = 9:1. This is a 9:1 exceedingly contrasty lighting considered theatrical. Note 9:1 is the maximum ratio. Any more reduction and the shadows will be void of detail. <br /> <br /> <br /> To review:<br /> Main at 4 feet fill at 4 feet ratio is 2:1<br /> Main at 4 feet fill at 5.6 feet ratio is 3:1<br /> Main at 4 feet fill at 8 feet ratio is 5:1<br /> Main at 4 feet fill at 11 feet ratio is 9:1<br /> <br /> <br /> It is no accident that the fill-to-subject distances follows the f/number set which is 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22.<br /> <br /> <br /> Note each value going right is its neighbor times 1.4.<br /> Each value going left is its neighbor divided by 1.4<br /> I call this kind of math gobbledygook </p>

[aleks_biteman]

<p>Thanks Alan, I appreciate all the info, just found out I got 7th out of 30... Not so happy about that lol. I was supposed to be one of the top contenders too! Stupid mistake... And this was my last chance to make it to nationals, time to go drown my sorrows in some music haha, thank you to both of you. </p>

[ellis_vener_photography]

Aleks, you had it backward. If your key is f/8 and you wanted a 4:1 ratio, the fill should meter at f/4 - two stops less than

your key. Think of the expression as a fraction : the fill light is 1/4 the brightness of the key.

 

Not it was likely covered in your test but fill light can have the same basic qualities of a main light - hard and specular or

soft and diffuse, broad or tightly focused, etc. And it can come from the side, the front, the top, or below, and it can have a

different color than the main or key light.

[JDMvW]

<p>Alan, that's a very helpful "musing".</p>

<p>Too bad, Aleks.</p>