When to use colored flash diffusers / flash covers?

[iggers]

I just ordered a cheap plastic pop-up flash diffuser. It has a platic holder that fits into the hot shoe, and three different hard plastic attachments that are held in front of the pop-up flash to diffuse the light. One is white, one is blue and one is red. I understand that the point of the diffuser is to, um, diffuse the harsh light from the flash. But what would a typical use for a blue or red one be? Has anyone used these? (I guess I'll find out soon enough.)

BTW: The Gary Fong "name brand" ones cost $20 or more, plus shipping. They might only come with the white cover. The one I bought was $5.99 plus $4 shipping ($5.25 to Canada).  Only minutes after paying for my item I was googling "pop-up flash diffuser" and found the same thing, with all three covers, at http://www.focalprice.com, for a mere $4.25 with free US shipping.)

[Justin Smith]

I suspect the red and blue filters are just for fun, like the Lomo Colorsplash or the Holga Color Flash. Here is a Flickr group with some examples.

I've seen examples of commercial photographers using colored gels over their strobes for mood lighting or to simulate morning or evening sunlight.

Below are a few shots I made at work a couple of years ago, just messing around with my Canon A70 and remote Sunpak flash triggered by an optical slave. My gels/filters were colored, translucent Rolodex dividers. I was trying to make our plant look more interesting for a website by adding some color; ultimately, they kinda looked overdone and we decided not to use them.

[KirkT]

If, for example, you use a red filter over your lens and a blue filter over your flash, then whatever the flash illuminates will be normal looking but everything else will appear red.

At least I think that's how it worked.

[Kin Lau]

With the _orange_ one (not red), if it's the right shade, can work like a CTO gel. That will let you balance your flash with tungsten lighting, so that your flash will have the same white balance as the warm tungsten lights.

[Alan Gage]

I'm with Kin. Usually colored gels are to give your flash the same color temperature as the ambient light so you can blend the two better. But if all the light is being provided by your flash and you're totally overpowering ambient than it doesn't matter. An orange would help balance with tungsten and a greenish one would be for Fluorescent.

Also, that flash diffuser by itself doesn't soften the light from your flash. Step outside on a dark night and take two shots, one with the diffuser and one without, they'll look the same.

The only thing that controls how "hard" or "soft" your flash is is the relative size of the flash to the subject. A relatively larger light source gives a softer light and a small light source makes a hard light.

The sun is very large but also very far away, making it relatively small and creating a hard light. Your flash is very small but if you put it 10 inches away from a fly it would be huge compared to the fly, making for a very soft light if you were to photograph it with a macro lens.

So what's the purpose of your diffuser then? It's for using bounce flash. It scatters the light and allows some of it to directly reach the subject and for some of it to bounce off walls and ceilings first. Walls and ceilings are big light sources depending on how much of them you light up and make multiple soft sources when using a diffuser like that.

Of course the effectiveness all depends on how far away they are from the flash and the subject and how powerful your flash is. As you can imagine scattering the light all around the room takes a lot more power than just pointing it directly at the subject.

Alan

[JRJacobs]

I like to use colored flash for FUN!