Yesterday was a great day. I learnt a ton from a great teacher — let us call him Jim. He is sharp and very responsive to my questions. No wonder I learn best when I can question, not for the sake of questioning, but getting my fundamentals right.
I captured some lessons for the benefits of others to learn, discuss, debate, etc. Please feel free to do so using the “Comments” section.
| Note: I am posting this without pictures, just to get it out on the blog. I will post the pictures soon to go along with article. In the meanwhile, please use your imaginative mind! |
#1: Inverse square law is your best friend
If you don’t, you better internalize this like breathing. Simply put, the law says, the power of light at a point is inversely proportional to the square of the distance from the light source. Come on, you are technical enough to understand this!
Let’s say you have a light source pointing at a subject, and distance between them is one foot. If the background is a foot from the subject, the background gets 1/4 the amount of light falling on the subject. Meaning — the background is 2 stops below the subject.
Why does this matter? For one, you could easily darken the background, even if it is a light one. How? Think about it, if I make the distance between the light source and the subject same as the subject and background, the background gets light 2-stops below what the subject is. If you metered well for the subject, the background becomes darker. If you have a white background, it comes gray. How simple can changing your background be, without using gels!
Also, this factors into if you should use a reflecting umbrella or a shoot-through. A reflecting umbrella adds additional distance to the subject, so you will need more power to light your subject. Simply reversing this, and using the umbrella as shoot-through, you can get the light closer to the subject — imagine all the savings in the power, batteries, etc.
#2: Plan your set-up space for reflections AKA consider a softbox
The inverse square law is within ideal conditions — meaning, the light falling on the subject comes from one source only, and there is no other source. But come to think about it, there could be multiple sources within a studio — walls could reflect, so can other things within the set-up. This is where a softbox or a strip light needs to be considered. Softboxes make the light directional, unlike shoot-through umbrellas which diffuse light in all directions, hence increasing the potential for reflections. By directing light in one direction using softbox of strip light not only reduces this, but also gives you controlled lighting.
#3: Rule of thumb: Stop down about 4 stops to cut off the ambient
Assume a normal exposure for a scene, lit purely by ambient is f2.8 at 1/15 (dim light). If you stopped down the camera 4 stops or more, the resulting picture would be dark — as if there were no light. Once you have done this, strobe lighting becomes the sole light source for you to paint the picture.
The question is, which of the Aperture, Shutter Speed or ISO would you change to get this change in stops? Any of the above, but if you plan to use strobe lighting, it almost is Shutter speed. However, if the ambient is too strong (too many windows open), you can change shutter speed or aperture, but try doing it merely with shutter speed as you will have much more latitude with aperture.
So, in the above example, you could meter to f2.8 at 1/250 and you have a lowered the exposure 4 stops. What if your sync speed is only 1/180? Then you could work with f4 at 1/180 and get the same effect.
The rule is just that — you can break it if you want, but make sure you have lowered exposure at least 2 stops, else the final picture will contain too much ambient light.
Another side point, if setting your shutter speed to the sync speed gets you 4 stops or more, simply set it to the sync speed. Stopping down the shutter will only help cut off ambient.
#4: Open up the aperture to save flash power AKA “Shutter controls the ambient, aperture controls the flash”
It is well-known fact that the shutter speed has absolutely no effect when using a flash — the flash occurs for a very small amount of time, much smaller than the sync speed on most cameras. A typical sync speed is about 1/200 second, and the flash duration is usually 1/1000 or smaller.
This means, the only way you can control the exposure by flash is by the aperture. Think about it: When the shutter has opened and closed, the flash is already done firing, and is relaxing for the next shot. Making shutter go faster has no bearing, and besides, you cannot make the shutter go faster than sync speed. However, if you stop the aperture down, you let a smaller amount of this light through.
Ambient, on the other hand, is a constant light and hence can easily be controlled by the shutter speed. As mentioned in point #3, save changing the aperture until you start working with strobes. The biggest advantage of this is, with larger apertures (as in small F numbers), you will need only small power from the flash. This will not only save batteries, but with some flashes, like Sunpak 383s I use, you can get more flashes with single recycle. If you are using larger strobes, like Alien Bees, you will see this benefit as well.
#5: Setting the flash power levels
All flashes, manual or automatic, have power setting guides — based on the ISO, f-stop and distance to the subject. I have noticed that these are fairly accurate when the flash is used without any modifiers. When you use a modifier like an umbrella, you lose about 1-2 stops. That means, you should easily be able to set the power levels without taking too many test pictures.
#6: Balancing the ambient and flash is easier than you thought
This is best when you work outdoors, and there is a bright background — bright daylight, sunset, etc. If you have a person against the background, you will notice that the person is either silhouetted or just simply not exposed well. You could use the flash as a filler in this dark space, but the question is how.
Let us say the metering for the background is f8 at 1/500. To match the sync speed, it becomes f13 at 1/180. Set this in your camera, and set the camera power appropriately (as mentioned in #5), and shoot away!
You can create nicer pictures by subduing the background exposure — by simply stopping down the shutter speed 1-2 stops, depending on how dramatic you want the contrast. Remember, use shutter speed, not aperture, to control the background/ambient.
