味久摄影
摄影学习 - 持续光源和闪灯, ZT
Continuous lighting (also known as hot lights or tungsten lights) are lights that are on all the time.
Flash (also known as strobe) is just a brief flash of light, delivered at the precise moment that your camera shutter is open.
- Continuous lighting seems easier to use because you can see it, and you can see the effect it will have on your photos - where the shadows will fall for example.
- Another advantage of continuous lighting is that it will work with pretty well any camera (if flash is used the camera will need to have a PC socket or a hotshoe, and can't be used on automatic exposure settings)
- Leaving aside the specialized professional lighting equipment, there are 2 basics types of continuous lighting, tungsten and fluorescent. Tungsten lights are similar to ordinary household bulbs, although the better ones are quartz halogen, similar to security lights. Fluorescent lights are similar to ordinary household fluorescents, and sometimes are exactly the same.
- Tungsten lights burn hot - very hot - and so although they can be fine for photographing still life subjects they really aren't ideal for photographing people, partly because the heat is uncomfortable and partly because, although they seem to be very bright, most of the power turns to heat and quite long exposures are normal, which can create blurred pictures.
- Tungsten lights also carry a very real fire risk
- Tungsten lights are much 'warmer' (more yellow) than flash. If you're shooting on digital then this can be corrected on your camera and won't matter (as long as all the lights are the same colour) but if you're shooting on film you should use filters to correct the colour - which absorbs a lot of the lighting power.
- Tungsten lights can't be adjusted for power, so if you want a more powerful light you have to use a brighter one and if you want less power you have to move it further away, which completely changes the lighting effect and causes harsher shadows.
- And if you use a softbox to diffuse the light it will need to be designed specially for tungsten lights and will cost more
- Fluorescent lights have the advantage of being cool-running and some can be adjusted for power, although the adjustment usually consists of turning off one or more lamps within the light fitting, which is a far more restricted range of adjustment than the adjustment available on most flash units.
- Fluorescent lights are also 'white' and approximately match daylight. However, this in itself doesn't make them suitable for photography because what really matters with fluorescent lights isn't the colour temperature but the Colour Rendition Index (CRI). Colour rendering describes how a light source makes the colour of an object appear to human eyes, film or digital and how well subtle variations in colour shades are revealed. The CRI is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering colour when compared to a "reference" light source such as sunlight. The higher the CRI, the better the colour rendering ability. Light sources with a CRI of 85 to 90 are considered good at colour rendering. Light sources with a CRI of 90 or higher are needed for photography so a CRI of 90 is the minimum acceptable standard for photographic lighting - so find out the CRI of any fluorescent light source before buying it, don't assume that just because a seller claims that their lights are suitable for photography that they actually are suitable! Both sunlight and tungsten lights have a CRI value of 100 and this allows all colours to be rendered (reproduced) accurately
- As I mentioned before, tungsten lights come in 2 types, 'bulbs' and quartz halogen. Quartz lights usually last for around 1,000 hours and they keep to the same colour and the same output until they fail.
Photoflood bulbs are cheaper, but they only last for a few hours and they become darker over their short life. They've been discontinued now but some people still sell them... If you really must get tungsten lights, get quartz ones.
Flash is a much more professional solution.
Advantages:
- The flash is very short (often around 1/1000th sec) so will 'freeze' most movement
- There is no heat, so far more comfortable for both you and your sitter
- The flash is about the same colour as most daylight, so no filters or other adjustments are needed and you can combine flash with daylight if you want to
- Much safer too, little or no fire risk
- Acessories such as softboxes are much cheaper and more efficient
- Far more accessories are available
- Far more power, so smaller lens apertures can be used
- They use less electricity
But there are some disadvantages too
- They can't be used with the very cheapest cameras
- They require more care and knowledge to get good results
- Unless they have bright modelling lamps (see separate article on choosing studio flash) it can be difficult to see the effect that the flash will have
So which should you choose?
Well, tungsten lights can produce perfectly good results for some types of photography and are cheaper, but flash is a far more professional solution and is the tool of choice for nearly all professional photographers. My training course on Studio Lighting and Equipment goes into a lot more detail than this short guide.
I hope this helps you to make your choice. Not everyone will like this guide - for example the people who sell the type of equipment I'm advising against may find it unhelpful because people will make better choices, so please be sure to let other Ebay users know if you've found it helpful. The more votes it gets, the more visible the guide becomes and the more people will benefit from it.
Combining Flash with Continuous Light Sources
How To Balance Flash with Moving Continuous Light Sources
Ever see those photos that pop up in the Flickr pool that combine strobe and moving lights? Putting light sources in motion -- or capturing lights that move on their own - is fun. But balancing them with strobe means solving for two variables.For some shooters that can get a little complicated, but it doesn't need to be. More after the jump.
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The Movement Is Your Shutter
The first step in balancing lights-in-motion with flash is to realize that moving light sources are very much like flash, in that their exposure is aperture-dependent. Take the fire juggling photo above for instance, which is by reader Hugh Beauchamp.
The fire in this photo is continuous, so its exposure is determined by both shutter and aperture. But since the continuous light source itself is moving, the speed at which it is moving already determines the effective shutter speed for a given place in the photo.
The faster it is moving, the less time the fire spends on any one spot on the frame to burn itself in, so to speak. So the speed of the motion of the flame is, in effect, it's shutter speed. Assuming a reasonably constant speed, the total exposure is now going to depend on the aperture. (It'll also depend on the ISO, of course, but let's zero that out for the sake of simplicity.)
Let's assume a dark environment. To duplicate the technique of Hugh's spinning fire shot, the process would simply be this:
1. Set your camera to a reasonable ISO. Say, ISO 200, for example. Lock down in a tripod.
2. Get your subject to run through the motion at normal speed as you shoot a few test exposures.
3. Varying the aperture and chimp the back of the camera until you like the look of the burned-in flames.
Now, you have your working aperture, and your shutter is going to be determined by how long and complicated you want the fire "tracks" to be. In this case, Hugh shot at f/10, for 1 second. (He was shooting at ISO 100.)
Now that you have a working aperture, it is a simple thing to adjust your flashes until you get the level of light that you want on your subject. Given that Hugh was shooting against a dark background, he wisely chose to use back/rim lighting to define his subject. This gave him dramatic light (which worked well with the fire) and good internal separation of his tones.
Hugh also chose to include his flash in this photo, which I like. He could have killed the light stand very easily by running a strip of matte-black gaffer tape down the front pole and legs, but now I am just being picky.
You can see Hugh's full lighting setup here, which is basically back/rim lighting plus a CTO'd flash for the face.
You might be thinking it would have been cool to do this at twilight instead of at night, But that's gonna make the whole thing more complicated, as now you have to worry about the sky "burning in" through parts of the juggler as he moves. Not to say that it can't be done. Just gets a little more complex as now you have to worry about your background tracking in various parts of the frame.
Cool shot, Hugh. And for those of you thinking of trying it: Please make sure you have a couple of buckets of water on hand. And resist the urge to keep shooting -- no matter how cool it looks -- if the whole field goes up in flames.