Flash diffusers: The good, the bad, and the ugly

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Flash diffusers: The good, the bad, and the ugly

Postby Citruspers » Mon Jan 04, 2010 8:25 pm

Flash diffusers: The good, the bad, and the ugly

Probably the most overpriced piece of crud in the history of photography, the so called diffuser dome can be found in almost any hotshoe flash
photographers bag. Ranging in price from a couple of dollars to 60 dollars for the "specially crafted" variants, they all share one thing common: people often do not know how to use them.

Let me start first by explaining what it is. The diffuser dome (hereafter referred to as the diffuser) is mounted on the flash, in order to spread light all over the room. This invention was neccesary after photographers switched to flash tubes on hotshoe flashes, where early photographers could just unscrew the reflector to achieve the same. Shooting with a diffuser is sometimes referred to as "shooting bare bulb".

This is also where the diffuser got it's name. It diffuses the light across the whole room. And here is where the chaos starts. Diffuse light means the light is going everywhere (does not have one general direction). However, many photographers use the words "diffuse light" to indicate a certain softness of the light. Here's the catch: light coming from a diffuser is not soft in any way!

Softness of light is dictated by the relative size of the light source. If the light source is small, a subject will cast a very sharp (well defined) shadow. This is called harsh light. However, if light is coming from an infinite number of directions, it will cast a softer gradient from areas of light, and areas of shadow, because more is illuminated.

A diffuser works on this by spreading across the whole room, essentially making the whole room your light source. This of course only works if you have a very big white room (also known as a studio), in which case you probably have something better than a diffuser to light your subjects.

Now we are coming to the most common misconception: a diffuser makes your light softer. No, it does NOT. Take a look at your flash bulb. It's not very big. Now pop on the diffuser and look again. Is it bigger? Yeah, a couple of millimeters. In other words: not field-relevant. What you need is a large light source, like a wall, to become your main lightsource.

So how do we define large? The sun is quite large yes? However, if you read carefully, you noticed I said "relative" a while back. The sun is still a very harsh light source, because it's further away. That's also key to getting soft light. The closer you position your subject to the wall you are bouncing from, the softer it will be, because it's relatively larger!

Very often, I see people with diffusers on their flashes, outdoors, thinking it will make their light softer. Now you know it does not. It actually has
one negative aspect as well. Because the light is spread everywhere, you will lose around 2 stops of light. 2 stops! That means if you are shooting at full power, your actual light output will be 1/4 power! You'd have to use 4 flashes with diffusers, or one without to get the same exposure outdoors.

You're wasting your batteries!

So in the end, are diffusers still worth buying? I'd say yes, but get the cheapest you can find. It can work in white/gray rooms, but remember light picks up the colour of the object it hits. If you use a diffuser in a blue room your subject will become a smurf.

So that's it. Now you know when to use a diffuser (and more importantly, when not).

One final note: you may have seen the lumiquest softboxes for on-camera flash. These are NOT diffusers. They create a bigger lightsource from your camera flash, and we all know what that means: (all together now!) SOFTER LIGHT, yaaay!

And that's our final bottom line. Try to create the biggest light source you can, any way you can. I shoved a large white paper bag over my flash at an event.

It worked! :lol:
I take pictures so quickly, my highschool was "Continuous High".
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Postby frs69 » Sat Jan 16, 2010 4:37 pm

Hello Marijn :) ,
It was about time for the diffusers as anyone barely talked about it. I have made a Pdf out of it :wink: Why no more posting of some new shots with the primes. I hope your busy week is over today. Is it? :roll:
Pleasure to have you around.

Ps: Btw, check that video Bjorn posted of Zach Arias. it's cool. You'll love it.

Postby davix » Mon Apr 12, 2010 9:45 pm

After just recently purchased a SB-600, I considered a diffuser, but they were charging 30 bucks for it. And just as you said, it's just a piece of plastic. So I made my own, a white piece of cardboard strapped onto the flash by some elastic bands.


Postby Anel-slo » Mon Apr 12, 2010 10:01 pm

was never a fan of those plastic things that "diffuse and soften your light dramatically", i once used a plastic bag outside, made some wonderful light, a cardboard thing that basically doubled the size of my flash and of course umbrellas and bouncers..

Postby Austin » Tue Jun 01, 2010 3:08 pm

I can't imagine the mark-up on those little pieces of plastic! Not really worth it at all, if you ask me.

Now, just today I tried a light sphere. Gary Wong sells a few kinds, but I tried one from Japan. It did pretty well. Has anybody tried one?
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Postby EvanK » Wed Nov 23, 2011 6:23 am

Thanks for the post, Marijn. I just came across it and it was a great read.

Would you recommend any of those Lumiquest on-camera softboxes? Do they really make a noticeable difference? Sometimes I take photos for friends in indoor venues with high ceilings where light can't be bounced and direct light is too harsh. Would they work well in a situation like this?


Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories

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Postby Trevor Harris » Wed Nov 23, 2011 11:56 am

Hey Evan,

Yes, they would create a more softer light - but it's all in proportion. If you put one of those soft boxes - The largest one being 8"x9" (which is really big considering the variety of them), and knowing that your flash head is about 2"x1":

(8x9) = 72
(2x1) = 2

Thus, increased area: 32.

That sounds like a lot - but lets consider that you're likely used to seeing studio portraits with umbrellas and soft boxes. A 45" umbrella has an area of 1590.

So, your increased area then becomes: 795.

Knowing that softness is proportionate to area... well... you get what I'm saying. The softbox will help, but in relation to studio work, it doesn't compare.
Trevor Harris

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Postby Radu » Wed Nov 23, 2011 6:36 pm

and may I add that Lumiquest soft boxes won't take the flash out of your lens' axis.
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Postby Citruspers » Wed Nov 23, 2011 8:54 pm

Cheers Evan!
The softbox makes a difference, but not much. Dealextreme has a very cheap one that's rather flimsy, but light and cheap: http://www.dealextreme.com/p/universal- ... mera-37666

I don't use mine though...:p
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