I'm sure some of you have tried to use a popup flash diffuser on a Canon DSLR before. If it is one that attaches to the hot shoe, you have probably realized this dosent work so well. Canon's have a sensor that disables the popup and the flash settings when the sensor is depressed with in the hot shoe. With this being said you would need to raise the flash then slide the diffuser into the hot shoe, then pull it out a little so that it dosent depress the sensor, disabling the flash. This makes for a pain in the butt time taking photos. So I added some mod's for full on the fly functionality.
Step 1: Barrier
The flash diffuser will go in to far if this barrier is not in place. This is a cheap solution.
Air line for a fish bubbler. I just cut a small section and placed it under the fine pieces of metal that press down on the sensor. by
You can stop here if you want. The sensors will not depress nor will the hot shoe mount be able to go in far enough to contact the sensors disabling the flash popup. Just keep in mind that your defuser can come out and you may not see it drop leaving it behind. $20.00 down the drain.
Step 2: Drill
I know, scary, but its just plastic. I drilled holes in the center above the hot shoe mount on each side of the diffuser.
Then I drilled a hole on each side of the diffuser arms.
Step 3: Elastic Threw The Plastic
Simply thread elastic threw the holes meeting both ends in the center of the hot shoe mount, creating a loop.
Step 4: Crimp
I grabbed some crimp style wire connectors. I cut the plastic. coating off of one. I then cut the wire connector down to a size that would fit between my hot shoe mount with a bit of wiggle room. I quickly ran it over a file just to remove any burrs.