Friday, 31 January 2014

Poly-board Tunnel - Fashion Portraits - Diffuse Light

This is another light set-up that we cover, that produces an exceptionally soft diffuse wrap-around light. It requires a fairly large studio space because you need to make a large box shape construction out of your 8'x4' poly-boards. You'll need the following equipment...

2 x studio flash heads and appropriate light stands.
6 x Poly-boards 8'x4'.
A table (typical school table).
Optional backgrounds.
2 x small light stands.

Place the table in the middle of the studio space with an appropriate (white) background behind where the subject/model is stood (A). Construct the square shaped tunnel on top of the table (See second diagram). The sides need to be supported by small extended light stands either side of the poly-boards as you construct it, you should also work with an assistant to make the whole thing easier and safer. Once the side are in place the top of the box should be carefully placed making a tunnel.

Starting with one light, either (E) or (D) set the light up so that it's just outside of the box positioned so that it's directing the light into the box at 45 degrees. Have the light so that it's positioned mid-way up the box, with the light angled into the box straight rather than downwards or upwards. The lights must not be visible to the model when standing at (A). You take your light reading from the face of the model pointing the invercone into the tunnel measuring the light falling onto the face of the model. Dependent on what you're aiming to achieve (Shallow depth of field or deep) make a choice with regards to your aperture. We would generally go for f8 for each flash head. They're measured individually and accurately (work to eliminate the 10ths of stops). Once they're both set to f8, the combined reading of both of them being fired at the same time will produce a reading of f11. At which point if your camera is set up correctly you're good to go!
This below is an approximation of a 3D view.
If you've not set the lights up with the poly-boards at (c) you'll probably experience bright panels of light either side of the subject in your images. The light travelling down the tunnels will be absorbed  to some extent giving you an image in accordance with your meter reading, but the light that passes down the outside of the tunnel is not hindered and may be recorded in the image either side of your model slightly brighter. In which case you need to prevent that light from falling on your background.
The effect is that a white background as with our infinity cover will be rendered slightly U/Exp. The further the box is from the cover the darker it will be.
3 Light system - pure white back-ground.
We then developed the set-up, by introducing a 3rd light (below) indicated by (j) in this instance we just used a dish-less head. The light was positioned so that the light fell onto the white B/G, but you have to be careful to ensure none of the light encroaches onto the model/subject to ensure the hatched area (b) is still maintained at around f11. The third light (g) is calibrated so that it gives a reading of around f16 (1 stop brighter). This modification of the lighting will produce a pure white background.

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