There are numerous flash diffuser instructables on this site but most of them are cumbersome, fragile, waste flash power and are not easy to pack.

To get really sharp macro photos you must use small apertures for sufficient depth of field and really rigid support and non moving subject. Or just use flash. The problem is that the photos sometimes look unnatural because the light is harsh and the illumination quickly falls off as the distance from the flash increases resulting in dark backgrounds. Macro flashes are expensive and since they are closer to the subject, the background is even darker. So I came up with an idea to illuminate bacground and the subject evenly with just one standard external flash.

This diffuser is intended to work in the macro range: 1:3 or larger magnification on an APS-C DSLR
It has the following advantages:
* cheap! You probably already have most if not all of the parts
* rigid and strong
* flat - can be taken almost everywhere and takes almost no space
* adjustable subject/background lighting

This is my first Instructable and also my entry to the Camera & Photo Skills Challenge
Vote if you like it!

Step 1: Materials

You will need:

* filter for your macro lens

Most macro lenses use 52 mm filters. These can be found dirt cheap everywhere and you probably have few of those in your attic. I used an old red filter and took the glass out but you can use clear/UV filter if you are afraid to cut yourself. Thicker is better.

* plastic jug - with a large flat surface

* knife or scissors
* 5 minute epoxy glue
* sandpaper

Step 2: Estimating the Size

Mount your lens and flash to the camera.

Focus the lens on the LOWEST magnification you will use with this diffuser. 1:3 to 1:2 for a 105mm lens is a good idea.

Connect the highest point of your flash to the highest point of your subject.

The heigt of your diffuser is where this line intersects with the filter (remember: the subject must NOT "see" bare flash!)

Using 1:2.5 magnification I estimated the height to be 11cm (~4.5 inches). Make it slightly larger - you can always trim it later.

Step 3: Cutting the Diffuser

This is easy. Cut it slightly higher than estimated and slightly wider - make a rectangle. I estimated 11 cm height and ended up with a 13 x 16 cm rectangle. The size is not critical as long as it is large enough - you can always trim it later.

Place your filter on the bottom part of the diffuser and cut a semi-circular hole for it.

Step 4: Gluing

Attach filter to the lens.

Mark the filter with a sharp knife so you know which side is up!

Then glue the piece of plactic to the filter using 5 minute epoxy. I strongly suggest covering the filter threads with tape - epoxy is very hard to remove afterwards!

Step 5: Adjustments

After the epoxy has cured attach the filter to the lens and take some pictures with various magnifications and varios background-subject distances, flash head zoom settings etc.

I was getting much more subject illumination and less background illumination than I wanted (this depends on the density of the diffusion material and shape of the flash beam). So I decided to slightly trim the diffuser - I cut around 1.5 cm off the top.

Afterwards I rounded the corners to get nicer specular highlights on shiny objects like, for example, water drops.

Step 6: In Use

After the finishing touches I made some test shots.

Step 7: Tips

* Zoom out the flash head to throw more light on your subject and zoom in to throw more light on background
* Slightly raise the flash head to throw more light to background
* Trim sides to throw less light to subject
* Use bounce card to throw more light to subject
* Use built-in flash to get dark backgrounds

* Have fun!