Where does this "looks like flash" idea come from? Has anyone ever tested continuous vs strobe?

Started 1 week ago | Discussions thread
john isaacs Senior Member • Posts: 2,225
Re: Where does this "looks like flash" idea come from?

modolover wrote:

(this question is only about the visual look or appearance, not about power, convenience, features, temperature, etc)

Howdy. I live by the motto that light is light, and regardless of the source they all [generally] are guided by the same principals and laws of physics. However, I was speaking to a well known lighting expert in my city and he told me that continuous/hot lights actually look slightly different. "In portraits, hot light has a subtle nuance to it, a subtle glow or smoothness because the quality of light is different at the source". I found this hard to believe if the bulb whether continuous or flash is modified the same way, under the same power. Then I thought, the different in using flash vs continuous is the shutter speed! Flash tends to kill any type of ambience while continuous lights can allow for a slow shutter speed to soak up the ambience. Perhaps this is how some old school film photographers achieved a "glow" in their portraits.

So I ask, has anyone actually conducted a test on this topic? I wish I could, but don't have continuous lights at the moment. Why is it that flash "looks like flash" and continuous light doesn't "look like continuous". Is it because the key light on the face is usually too strong when people use strobes? Where does the "looks like flash" idea come from if light is light after all?

Why is it that the extremely powerful hot lights used in cinema don't look artificial, whether using hard light or soft light, they always look very well balanced.

The "looks like flash" characteristic has four main components:

1. Dark background: Exposures are not set for ambient, so the background is dark and the foreground is brightly lit.

2. Straight on direction: Usually the flash is mounted on the camera; this gives a flat looking light that suppresses shadows on the subject, but produces unnatural shadows behind the subject.  It also puts catchlights in the center of the eye and can produce red-eye.

3. Color mismatch: The color of the light from the flash is similar to daylight, but when using flash because ambient light is low, then the ambient light often has an orange tint (this can be from a rising/setting sun, or from incandescent lamps).  Or the light can have a green cast from flourescent lighting.

4. Speed of the flash effects: Common effects are to freeze motion, as well as catch pupil dilation.

These can be corrected, for the most part, by taking several steps:

To correct dark background, set exposure settings so the background is close to correct exposure.  Usually, this means increasing ISO because shutter speed and aperture are used to control for other aspects such as motion blur and depth of field.  Or increase the background light; turn up the lights or add some background flashes/strobes.  Then the difference between the lit subject and background will not be so severe.

To correct for directionality, get the flash off camera, and use a modifier (umbrella, soft box, reflective surface like wall or ceiling).  Diffuse light coming from an appropriate direction will reduce or eliminate the noticeable issue of on-camera flash.

To correct color mismatch, add color gels to the flash to match background light.  This can be done just by experience, or by using a color meter.  Accurate color meters can be very expensive, but you can use a smart phone camera and app and a white dome attachment to get decent color temperature measurements and advice on what gels to use.  I use Cinemeter II with a Luxi, but I only correct by 1/2 or so because I think a little color tint to the background looks more natural.

To correct for the effects of high speed flash can be more difficult.  You can use red eye reducing pre-flash to constrict pupils.  To solve the issue of freezing motion is more challenging.  Sometimes, just taking a number of exposures in quick succession and blending in post can help with things like fountains and running water.  But I've found that in these cases, continuous lighting can be the only solution.  Some flashes have modeling light functions, or even added LED lights for video, and these can be used when needed.

As far as your question on cinema lighting; the lights are gelled for color correction.  Higher end video lights allow adjustment of color temperature.  Cinematographers and videographers often use expensive color light meters for this purpose.  Compared to the cost of their cameras and lenses, the light meters aren't that expensive.  Compared to the normal persons equipment, they are quite expensive.  Again, I suggest exploring a smart phone app; it will get you very close.

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