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" Found way to make cheap soft box"



 
 
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  #1  
Old April 8th 04, 05:20 AM
Adrian
external usenet poster
 
Posts: n/a
Default " Found way to make cheap soft box"

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  
Old July 11th 04, 09:49 PM
Robert C.
external usenet poster
 
Posts: n/a
Default Found way to make cheap soft box"

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  
Old July 11th 04, 09:49 PM
Robert C.
external usenet poster
 
Posts: n/a
Default Found way to make cheap soft box"

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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