Do-it-yourself flash diffuser for macro photography

Uploaded 29. Jan. 2012
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I strongly disliked flash photography for quite a long time. Since a flash generates hard, unnatural light and distinct shadows, I was avoiding the use of a flashgun at all costs. I thought - and still think - that the natural, available light is much nicer and more pleasant than any artifical light source.

Why a flash can be useful

There are, however, quite a number of situations where the available light just isn't enough. This is often true for macro photography: if you're working on real close-ups, your depth of field becomes increadibly narrow. This means you have to close down the aperture to get a decent range of sharpness, which results in prolonged exposure times. Things get even worse if the prevailing light conditions are poor: On my first trip to the rainforest I was amazed by all the macro opportunities around me, but at the same time shocked about the bad light conditions with the dense forest canopy blocking out most of the sunlight. So even with a sturdy tripod you can end up with several seconds of exposure - time enough for some little critters to just hop off. In such a situation, a flash would be of great help. But the negative aspects of flash photography mentioned above still prevail: hard contrasts, harsh shadows and annoying reflections on your subject can diminish the benefits of a shorter exposure. This is where a flash diffuser comes in: the diffuser softens the light of your flash and distributes it more equally around your subject, thus preventing hard shadows.
While any semi-translucent white material can be used as a diffuser, we wanted a light, foldable version specifically for macro photography.

Flash diffuser used in the dim light conditions of a tropical rainforest.

DIY Flash diffuser

A do-it-yourself flash diffuser is very easy and cheap to make. We just used some cardboard, aluminium foil, electrical tape and a bit of white foam packing. The following manual refers to a diffuser explicitly built for a Canon Speedlight in combination with a 100mm macro lens -  but since all external flashes of the major brands have both roughly the same shape and a tiltable head, this setup will work for a wide variety of flash/lens - combinations. Here's how to do it:

First, find some light but durable cardboard and cut out the four pieces forming the bottom, sides and top of the diffuser.
The left image shows a sketch including the dimensions of the pieces (click on image to enlarge).

Gluing aluminium foil on the inside of the cardboard will reflect the light from the flash towards the diffuser.
Hint: If you crumple up the foil before gluing it on, this will increase the diffusing effect.

Use adhesive tape to further fix the aluminium to the cardboard and prevent the foil from peeling off at the edges.

Connect the big top piece with the adjacent sides using electrical tape, then add the bottom piece to complete the cylinder. If you leave a small gap between the cardboard pieces, the whole construction remains foldable and can thus be stowed away easily. Be generous with the tape, since it gives your diffuser some degree of water repellence. We ended up covering the whole exterior of the apparatus with electrical tape and the diffuser survived a four-month long stay in the humid tropics.

Finally, find some diffusing material like white synthetic foam, styrofoam or sandwich paper. Your choice of material will influence the amount of transmitted light as well as possible colour casts (which both can be corrected via flash compensation and white balance, respectively). Try to find a material that suits your needs best and use it use it to cover the whole front opening. We cut out a piece of white foam packing, which can be wedged into the opening. The only thing to hold it in place is a peg. This way, the white diffuser is not permanently fixed onto the cardboard construction and so the whole setup can be folded up sideways to nicely fit into any camera bag.

The left picture was taken with a bare flash - note the harsh shadows and the specular highlight on the shell.
The picture on the right was taken using a flash with here described self-made diffuser; both shadows and reflections are noticeably reduced, the lightning is more homogeneous.

Have fun building your flash-diffuser!
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