Afternoon
I'm going on the premiss that there's no such thing as a daft question and hope not to prove that wrong!
I have some really basic questions i'm sure, just need to get my head around off camera flash and I thought here would be a great place to ask.
So, I've been watching a load of videos and I'm not sure i understand, people seem to set up lights, meter and then use the settings on their camera, I get that but does that mean the light dictates what you do in camera? I see videos where people meter at say f22 or f35 or something, what if I want to use a lens wide open on a portrait for example, is it just a case of lowering the power of the strobe? I'm wondering why people expose to the lights rather than setting the lights to match what they want from their lens or from the shot?
Soft boxes, are the differences in shape only changing catchlights in the eyes or is there another reason for an octabox over a regular square or rectangular box?
I keep hearing people talk about "soft wrapping light" what does this really mean as I'm sure light only goes in straight lines regardless of the source, what am I missing here?
What advice would you experts give someone going in to flash photography for the first time? Any pearls of wisdom you wish you'd known before embarking on this journey?
Many thanks in advance, hopefully these aren't really daft questions!
Mat
Hi Mat, let me see if I can help you out a little.
The basics of light are
1) Direction of Light, 2) Quantity of Light, and 3) Quality of Light. This applies to natural ambient light as well as artificial light. The difference being you control the
"when, where, and how" with artificial lighting.
1) Direction of Light is why you are interested in off-camera use of strobe lights. Rather than the flat head-on light provided by an on-camera speed-light, off-camera lighting allows you to alter the direction at will for creative reasons. Speed-lights do have their place, they can help fill deep shadow areas caused by harsh directional ambient lighting … outdoors or indoors.
2) Quantity of Light can be a function of whether you are using lights outdoors on a bright sunny day, or indoors in a dark studio. It takes more light to overcome the sun on a bright summer day with its' bright highlights and deep shadow areas, or back-lit scenarios. In studio, you have more control since you are creating all of the light.
People may be metering at f/22 because the highest shutter speed you can sync a focal plane camera at usually ranges from from 1/180, 1/200 or 1/250. So, the only way of controlling bright ambient is to stop down, and then increase the amount of lighting on the subject. The objective of this exercise is "light balance" between the ambient background, and light falling on a closer subject. How well one masters "light balance" determines the natural feel of the image as opposed to that "over-flashed" look.
Note: Leaf shutter cameras can sync from 1/500 (Hasselblad V), 1/800 (Hasselblad H), 1/1000 (Leica S2/CS lenses and some Rollie), and even higher with P1 DF+/CS lenses and accessories. This is why they are desirable for certain types of flash photography, especially outdoors.
So, let's say we are shooting outdoors and at base ISO 100, lens set to f/2 for a portrait, and you are forced to a max sync shutter speed of 1/200th … you may already be near over-exposure … and adding light will guarantee it. Now that is an extreme example, but one I have run up against on beaches for example. However, most strobes have very low output settings which will allow you to place light on the subject in less extreme ambient using a wider aperture. This is measured in W/s which is referencing the energy released at that setting. For example the Profoto B1 moonlight offers settings from 2W/s to 500W/s. At 2W/s the light is essentially acting as mild shadow fill in a bright ambient scenario. For reference, a typical top end speed-light delivers about 80W/s at max energy settings.
Quantity of light may also be effected by a need for DOF … oddly, in studio doing closer shots requires a lot more light than you'd imagine because you have to stop down so much to retain DOF front-to-back on any given object.
Lastly, Quantity of Light is effected by distance to subject … to see how this works look up "The Inverse Square Law of lighting".
Quality of Light is the fun, creative part of lighting … strobes have a zillion different ways of modifying the raw light output. The primary thing to understand about lighting is how the size of the source affects the quality of light. Generally, small sources create a more specular quality of light, and bigger ones a more gentle quality of light.
So, terms like "wrap around lighting" are usually referencing a larger source like a big soft box that is placed closer to the subject … in effect it is like placing a subject near a large picture window with shear drapes. As you move that same light/modifier further away from the subject, the smaller it becomes and the more specular it can get. Think of the difference between the pin-point sun at noon and at big ball sunset … noon is harsh and specular, sunset is softer and more gentle. The amount of Earth's atmosphere the light travels through is why this happens.
Octa or square soft-boxes are variations on a theme … Octas have more facets inside to "shape the light" differently than a soft box with its' four sides. Octas also come in "deep" versions which can "magnify" the amount of light being thrown forward … providing more light to subject than a less deep modifier.
The other aspect of different modifiers is controlling where the light falls and doesn't fall. An umbrella offers less control compared to a soft box which can also use internal diffusion baffles and masking grids to be more exacting in light placement. For example, a gridded soft box can light the subject but not fall on the background which is harder to do with an umbrella alone.
There is a lot more to it, which is why is so much fun working with lighting, but that's the fundamentals to begin with.
I'll try to dig up a few examples to demonstrate the above.
- Marc