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#1
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Hi all
Some suggestions have been made about using a styrofoam cooler ($1.50) to make a softbox. While I find the idea fabulous, and I'm actually gonna implement it, I don't quite understand the need to line the inside with aluminum foil. It may stem from a misconception that a reflecting surface must ideally be metallic. A metallic (mirror) surface provides *specular* reflection. This is a reflection which preserves information about shape, size, and location of the light source. A white styrofoam surface provides *scattered* reflection. This reflection retains no information about the original shape, size, or position of the bulb (this is what you want, no?). It only preserves information about *quantity* of light, averaged over the reflecting surface. ( This quantity is the same as for the aluminum foil reflection). Now, in using specular reflection, the strategy is to spread the light evenly over the diameter of the reflector (to form a smooth spot of light) . This is achieved only by ensuring the reflecting surface has a specific, precise (--and different) angle at every point on its surface, to direct the light in parallel rays toward the subject. The shape that provides all the right angles in the right places is a parabola. Not a hemisphere, not some other ovoid, but an accurate parabola, and the light source must be suspended at a very precise location from the parabola. Deviating even slightly from this shape will produce a terrible light source, with pronounced bright and dark spots, totally unusable for photography (just look at the spot from a cheapo flashlight--imperfections in the reflector shape, bulb positioning, etc cause a poorly formed spot) Now the aluminum foil is probably creased and crumpled and is about as likely to emulate a parabola as I am to invent the airplane. The foil reflector could be modeled as several dozen to several hundred small mirrors, each having specular reflection. So you get many small reflections, each retaining a substantial amount of information about the appearance of the bulb it reflects, while sending this information haphazardly, in a way that has insufficient randomness to be likened to diffusion. Bright and dark spots galore. Moreover, and destructively so, because of the deep aspect ratio of the box, a lot of redundant reflection may occur ( this is reflection that keeps travelling back and forth between the same surfaces, without getting out of the box ). This is a waste of valuable strobe energy. In case you are tempted to invoke the 1st Law of Thermodynamics (energy is preserved), to reassure yourself that "all light must eventually get out the front, since it has nowhere else to go, and all surfaces reflect", picture this: a bulb completely enclosed at the center of a hollow metal sphere, with the inside surface mirror-polished. Plenty of reflection, all of it redundant. No light gets out (and it doesn't violate the First Law). My opinion is, you don't need the foil lining. I'd go with bare styrofoam reflectig surfaces, although I'd make some effort to place them at 45 degree angles from the horizontal (90 deg from side to side, top to bottom). That's the geometry with the most favorable chance of energy preservation. Adrian |
#2
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I made myself some softboxes using lightweight nylon material and fibreglass
rods. The difficult part was the centre ring and the corners, which I made out of aluminium. The entire softbox is made with white nylon, with the rear doubled with black nylon. The white acts as a diffuser. Total cost was about $15 for a 3' X 3' (1m X 1m) box + whatever lighting equipment you are using. "Adrian" wrote in message om... Hi all Some suggestions have been made about using a styrofoam cooler ($1.50) to make a softbox. While I find the idea fabulous, and I'm actually gonna implement it, I don't quite understand the need to line the inside with aluminum foil. It may stem from a misconception that a reflecting surface must ideally be metallic. A metallic (mirror) surface provides *specular* reflection. This is a reflection which preserves information about shape, size, and location of the light source. A white styrofoam surface provides *scattered* reflection. This reflection retains no information about the original shape, size, or position of the bulb (this is what you want, no?). It only preserves information about *quantity* of light, averaged over the reflecting surface. ( This quantity is the same as for the aluminum foil reflection). Now, in using specular reflection, the strategy is to spread the light evenly over the diameter of the reflector (to form a smooth spot of light) . This is achieved only by ensuring the reflecting surface has a specific, precise (--and different) angle at every point on its surface, to direct the light in parallel rays toward the subject. The shape that provides all the right angles in the right places is a parabola. Not a hemisphere, not some other ovoid, but an accurate parabola, and the light source must be suspended at a very precise location from the parabola. Deviating even slightly from this shape will produce a terrible light source, with pronounced bright and dark spots, totally unusable for photography (just look at the spot from a cheapo flashlight--imperfections in the reflector shape, bulb positioning, etc cause a poorly formed spot) Now the aluminum foil is probably creased and crumpled and is about as likely to emulate a parabola as I am to invent the airplane. The foil reflector could be modeled as several dozen to several hundred small mirrors, each having specular reflection. So you get many small reflections, each retaining a substantial amount of information about the appearance of the bulb it reflects, while sending this information haphazardly, in a way that has insufficient randomness to be likened to diffusion. Bright and dark spots galore. Moreover, and destructively so, because of the deep aspect ratio of the box, a lot of redundant reflection may occur ( this is reflection that keeps travelling back and forth between the same surfaces, without getting out of the box ). This is a waste of valuable strobe energy. In case you are tempted to invoke the 1st Law of Thermodynamics (energy is preserved), to reassure yourself that "all light must eventually get out the front, since it has nowhere else to go, and all surfaces reflect", picture this: a bulb completely enclosed at the center of a hollow metal sphere, with the inside surface mirror-polished. Plenty of reflection, all of it redundant. No light gets out (and it doesn't violate the First Law). My opinion is, you don't need the foil lining. I'd go with bare styrofoam reflectig surfaces, although I'd make some effort to place them at 45 degree angles from the horizontal (90 deg from side to side, top to bottom). That's the geometry with the most favorable chance of energy preservation. Adrian |
#3
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I made myself some softboxes using lightweight nylon material and fibreglass
rods. The difficult part was the centre ring and the corners, which I made out of aluminium. The entire softbox is made with white nylon, with the rear doubled with black nylon. The white acts as a diffuser. Total cost was about $15 for a 3' X 3' (1m X 1m) box + whatever lighting equipment you are using. "Adrian" wrote in message om... Hi all Some suggestions have been made about using a styrofoam cooler ($1.50) to make a softbox. While I find the idea fabulous, and I'm actually gonna implement it, I don't quite understand the need to line the inside with aluminum foil. It may stem from a misconception that a reflecting surface must ideally be metallic. A metallic (mirror) surface provides *specular* reflection. This is a reflection which preserves information about shape, size, and location of the light source. A white styrofoam surface provides *scattered* reflection. This reflection retains no information about the original shape, size, or position of the bulb (this is what you want, no?). It only preserves information about *quantity* of light, averaged over the reflecting surface. ( This quantity is the same as for the aluminum foil reflection). Now, in using specular reflection, the strategy is to spread the light evenly over the diameter of the reflector (to form a smooth spot of light) . This is achieved only by ensuring the reflecting surface has a specific, precise (--and different) angle at every point on its surface, to direct the light in parallel rays toward the subject. The shape that provides all the right angles in the right places is a parabola. Not a hemisphere, not some other ovoid, but an accurate parabola, and the light source must be suspended at a very precise location from the parabola. Deviating even slightly from this shape will produce a terrible light source, with pronounced bright and dark spots, totally unusable for photography (just look at the spot from a cheapo flashlight--imperfections in the reflector shape, bulb positioning, etc cause a poorly formed spot) Now the aluminum foil is probably creased and crumpled and is about as likely to emulate a parabola as I am to invent the airplane. The foil reflector could be modeled as several dozen to several hundred small mirrors, each having specular reflection. So you get many small reflections, each retaining a substantial amount of information about the appearance of the bulb it reflects, while sending this information haphazardly, in a way that has insufficient randomness to be likened to diffusion. Bright and dark spots galore. Moreover, and destructively so, because of the deep aspect ratio of the box, a lot of redundant reflection may occur ( this is reflection that keeps travelling back and forth between the same surfaces, without getting out of the box ). This is a waste of valuable strobe energy. In case you are tempted to invoke the 1st Law of Thermodynamics (energy is preserved), to reassure yourself that "all light must eventually get out the front, since it has nowhere else to go, and all surfaces reflect", picture this: a bulb completely enclosed at the center of a hollow metal sphere, with the inside surface mirror-polished. Plenty of reflection, all of it redundant. No light gets out (and it doesn't violate the First Law). My opinion is, you don't need the foil lining. I'd go with bare styrofoam reflectig surfaces, although I'd make some effort to place them at 45 degree angles from the horizontal (90 deg from side to side, top to bottom). That's the geometry with the most favorable chance of energy preservation. Adrian |
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