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Flash Softbox


Completed Softbox
This is my first attempt at building a softbox for my Sunpak 383 Super flash based on a design described by Gary Yelland.  My softbox is 200mm wide, 150mm high and 100mm deep.  It's constructed from whatever thin, dense cardboard I had lying around.  In this case I used an empty beer carton.  For the diffuser material I used old fashioned onion skin typing paper.  I found the typing paper lying around in a drawer.  It seems to work reasonably well, but I'll continue to experiment with other materials.

Softbox Plans
Click on the thumbnail to view the plans I used for my Sunpak 383.  You'll need to adjust the dimensions to match your flash.  A copy of the plans, formatted to print on an 8.5"x11" page at 300 dpi, is also available for download.

Mounting Collar
Start by assembling the mounting collar.  The length of the mounting collar should match the perimeter of your flash head.  Score and fold the collar so the two ends meet in the middle of the long side of the flash head.  Glue the collar splice piece across the join and hold it all in place with a rubber band until the glue dries.

Softbox Sides
Cut out the four sides.  Score and fold the tabs for mounting to the collar.  Assemble the sides into a pyramid.  I used reinforced strapping tape to secure the edges between each side.  Glue the tabs to the mounting collar and hold them in place with a rubber band until the glue dries.

Inner Surface
Cut out the mount for the inner diffuser.  Score and fold the mounting tabs and glue it into the center of the pyramid.  I used strapping tape to hold it in place while the glue was drying.  Glue aluminum foil to the inside surface of the softbox.  I found this to be an important step.  Without the foil the inner cardboard surface seems to absorb a significant amount of light.

Inner Diffuser
Cut a piece of diffuser material to the size of the inner mount and glue it in place.  This photo shows it taped in place temporarily.

Outer Diffuser
Finally, cut the outer piece of diffuser material and glue it to the tabs around the outside edge.  Again, this photo shows it held in place temporarily with tape.

Example 1
In this first example the flash is used as the only light source.  The shadow on the background is somewhat softer.
(1/200sec, f5.6, ISO 200.  +0.5EV exposure compensation applied to both frames during RAW conversion).

Example 2
In the second example I tried to mix in some ambient light with the flash by using a much slower shutter speed (1/15sec).  The shadow of the lampshade on the back wall is certainly more diffuse.  It turns out there are two problems with this example.  First, the exposure required for these two shots were very different.  In the first shot without the softbox I had to adjust the exposure compensation by -0.5 stop during the RAW conversion.  The second frame required +0.65 stop exposure compensation during RAW conversion.  The reason for the big difference turned out to be the flash's maximum power being exceeded.  The flash could not put out enough light to give a correct exposure for that subject distance with the softbox attached.  Example 3 illustrates this effect further.

The second problem is that the diffusion of the lampshade shadow is probably not the result of the softbox alone.  At the slower shutter speed the ambient light contributes more to the overall exposure and helps diffuse the shadow beyond the effect of the softbox alone.  Example 4 shows this in more detail.


Example 3
To get a feel for the maximum subject distance, while using the softbox, I took a series of shorts at increasing distances from the subject.  Up to 9 feet the shots have a similar brightness and the histograms are broad and shallow.  Starting at about 12 feet the brightness begins to drop off with a corresponding sharpening of the histograms.  It appears that the flash has enough power for a subject distance of 10-12 feet with the softbox fitted.

Example 4
This fourth example is more an example of blending the ambient light with the flash and less about pure softbox performance.  If you use your imagination, you can see that the shadow of the lamp shade on the back wall is better defined in the higher shutter speed shots.  At lower shutter speeds the ambient light contributes more to the overall exposure and helps diffuse the shadow beyond the effect of the softbox alone.  This suggests to me that automatically using the camera's max sync speed (i.e. maximum percentage of illumination from flash) isn't necessarily the best solution.
All Images © Copyright 2001-2009 Ian K. Chapple. All rights reserved.

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