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Flash – Which Flash Diffuser Works?


A flash gun light modifier is one of the first things people buy once they purchase an external flash. There are a lot of advantages of buying an external flash, better light quality, clearer photos, etc. But many people randomly fires their flashgun once the diffuser is on, which actually makes their photos look bland and flat. Our article here about flash modifiers will explain why this is happening.

Light Modifiers

In one of the forums that I frequently visit, there have been quite a few threads popping out asking about diffusers or light modifiers for on-cam flash guns, and you’ll read about some posters highly recommending one over another and pretty much all are denouncing the use of the flashgun without a modifier of some sort. Sadly, many after-market diffuser users are fed with marketing hype that feed on some buyers’ inadequate knowledge in flash usage, and mainly, how light works, in general.

Truth to be told, many flash modifiers work well when you have no surface to bounce the light off or you’re forced to fire it straight-on. However, almost none of them are worth their cost as you can make your own for just a few bucks or tinker with your flash’s power output and built-in diffusing panels to get the same result.

We’ll start off with the basics of light, and for the purpose of this article, we’ll concentrate on hotshoe-mounted flashguns.

Light travels in a straight line, once a flash is fired, unless modified, the light will travel on a straight line. It will not change direction unless it hits a surface that’ll force it to travel a different path. If the light emitted from the flash hits a surface that is parallel to the path of the light and that surface cannot completely block the light from passing through (such as a transparent glass or an opaque diffuser), majority of the light will go through that surface and still travel along the same path (unless the surface is at an angle that changes the direction of the light, such as a wall or prism).

What do diffusers do exactly?

ALL after-market diffusers scatter light that’s coming from your flash gun. These contraptions break up the linear path of the light by reducing the straight-line light’s output while adding opaque panels around the flash head so that the excess light will transmit sideways in addition to the straight-line light.

Light Path

Image 1 - Light Path

The keyword here is “in addition”, meaning the main source of light is still travelling straight, you just have more light spilling around the main light path’s beam.

What’s wrong with that?

Honestly, nothing.

The problem is how these products are being used and marketed (and in a way, what users believe it can do). The biggest selling pitch all diffusers use is their product produce a SOFTER light and LARGER light source. Unfortunately, that’s a convenient claim as the questions of “how much softer?” and “how much larger?” are never addressed.

A standard flash head’s size is roughly 3″x5″ in size, that’s a total surface area of 8 in² for the light source’s size. When you stick a diffusing cup such as an Omnibounce, your surface area is still roughly the same. When you install a bowl-type or flat-type diffuser like a Lightsphere, SpectraLight, or Pocket Bouncer, your light source size increases to roughly (5×3 inches+) 15-20 in². That’s only roughly 2.5x larger in apparent light size increase.

Remember the basics of light quality: The larger the apparent light source in relation to the subject, the softer the light.

Increasing your light source size from 8 in². to 20 in² aimed at a subject that’s roughly 100 in² (average human head width x height of 8×11 inch) makes very little difference or improvement as the modified light source is still a lot smaller than the subject. This difference is even less obvious as you increase the distance between subject and flash, as another basic light principle comes in where the farther the light source is the smaller its apparent size will be to the subject.

If you’re shooting subjects that are roughly the same size or smaller than your modifier of choice, then these diffusers will make a big difference as the light source is larger in relation to the subject’s size and you’ll probably be shooting pretty close to the subject.

How can you say that when there are “before and after” examples that clearly show how nice the light is when these products are used compared to direct flash!?

Here’s another genius marketing move, before I explain, I’ll show you some photographs that support the “big improvement” claim:

Bare flash direct

Image 2 - Bare flash direct

With Lightsphere

Image 3 - With Lightsphere

Big improvement, yes?

No doubt that the second photograph looks a lot more pleasing, but do you know why? If you said the light is diffused and the light source is larger with the diffuser on, then you’re only partly correct.

Direct flash has the light coming from the same axis as the lens, so the front of the subject is receiving the light first, then the light falls off in intensity as it moves further away from the flashgun.

With the modifier attached, the light from the flash is travelling upwards towards the ceiling, and the light intensity that’s travelling on-axis of the lens is reduced. The light that’s hitting the ceiling is bounced off and it fills the shadows behind the subject.

Note that the bulk of the diffusing is not done by the modifier itself but the room’s ceiling and walls. The light on the subject is altered by the surrounding walls and ceiling that allows the stray light from the modifier to bounce back towards the subject. If you take out all walls and ceiling, the modifier will not give you any difference in light quality as all the light that’s not travelling straight towards the subject is thrown out to open space.

Take a look at the next series of photographs.

Among the modifers in the market, only products like the Omnibounce can be used with the flash aimed directly at the subject, as other products (such as the Lightsphere, Spectra Light, Lumiquest, etc.) require your flash to be aimed at the ceiling.

Bare flash direct

Image 4 - Bare Flash - Direct

Omnibounce Direct

Image 5 - Omnibounce Direct

You can see from the photos above that the light quality of between a bare flash and the Omnibounce produce very little difference in terms of how the light looks on the subject. The shadows (refer to chin) are less pronounced with the Omnibounce as the scattered light used the walls around the subject to act as fill, which also brightened up the background a little. But if you don’t have nearby walls, the images will be almost identical.

Is the difference worth US$20? Your call.

Bounce it Off!

Let’s take a look at the other products that require you to aim the flash towards the ceiling.

Bare Flash - Aimed Up

Image 6 - Bare Flash - Aimed Up

Image 6 was taken with no modifier, the ceiling-bounced light instantly produced a softer light than the direct-flash as the ceiling now is our main light source. With almost all the light coming from the top, notice the soft shadows underneath the chin, nose, and eyes. The eyes also have little to no catchlight (light reflection) as there isn’t any on-axis, frontal light present.

Adding an Omnibounce with the flash aimed towards the ceiling (Image 7) ends up having most of your light hitting the ceiling (main light) and the sides of the Omnibounce acting as fill that directs on-axis light towards your subject. You can see this from the small catchlight on the subject’s eye.

Omnibounce - Aimed Up

Image 7 - Omnibounce - Aimed Up

However, notice that the Omnibounce created quite a bit of frontal light as well, as seen in the sharp shadow under the chin which was absent in Image 6. The subject is now lit with rather flat lighting compared to Image 6 and you’re getting the same shadow pattern as Images 4 and 5 (frontal light).

How about using a larger modifier such as the Lightsphere, for example? Let’s take a look at Image 8.

With Lightsphere

Image 8 - With Lightsphere - Aimed Up

With a larger dome diffusing cup, the light didn’t really change much from the Omnibounce aimed straight-up as the principle is the same, which is to throw most of the light to the ceiling (therefore illuminating the surrounding area and create softer light that’s coming from a 12-0-clock position), then use the scattered light around the flash head to throw some light forward, on-axis to the lens.

The result is very similar, you’d be hard-pressed to cite the differences of light quality between the two if we’re using a static subject. The resulting light is still quite frontal and flat with the catchlights registering as a small white dot right around the center of the iris.

This is a US$70 product versus a $20 product. Is the $50 difference between the Omnibounce and Lightsphere worth it? Your call.

Let’s take this a little further. We compared a couple of commercial products that cost quite a bit in Images 7 and 8. In Image 9, I’ve used a simple 3×5-inch white index card with the flash aiming straight-up towards the ceiling.

Bare Flash with Index Card

Image 9 - Bare Flash with Index Card

Frankly, that looks mighty similar to Image 7 and 8 that used commercial products, but this image used a modifier that cost as much as a stamp in whatever country you may be in right now. Are the results worth the $20-70 difference?

Image 9 has a bigger advantage in addition to the cost as well.

With less junk plastic blocking the light, the flash uses less battery juice allowing you to shoot more images. Also, you can adjust the height of the index card to control how much or how little frontal light you want to throw towards the subject. Your commercial diffusers cannot do that (without you spending more, that is).

Enough with all this frontal light!

The main question you should ask yourself is, if you’re planning to buy something to modify your light, are you using your flash to bounce light off larger surfaces? If so, read on.

When you bounce your flash off a wall or ceiling, you’re now using the ceiling or wall as your main light source. Unless the wall you’re bouncing off is unusually small, chances are, that surface will be significantly larger in surface area than your flash, resulting to much softer light.

Using a bare flash head, we’ve turned the flash 90-deg to the right and have the light bounce off a large wall resulting to Image 10.

Bare Flash Aimed At Wall

Image 10 - Bare Flash Aimed Towards Wall

With the main light source being the wall, we now have a very large light source (about 6ft² in size) in relation to the subject’s size (about 3ft seated). The light is coming from the camera’s right, resulting to a clear highlight-to-shadow transition from right to left. The photo provides better light quality and direction than any of the examples above without spending an additional cent.

As soon as we add a commercial modifier, however, we will re-introduce flatter-looking, frontal light even if the flash head is aimed at the wall, with less transition from highlight-to-shadow (note how similar the tones are across the face and the familiar chin shadow).


Image 11 - Omnibounce Aimed At Right Wall

Lightsphere Aimed to Right Wall

Image 12 - Lightsphere Aimed At Right Wall

The “scatter-light-all-over-the-place” approach of after-market diffusers create a “bare-bulb” effect on your flash which makes aiming your flash around surfaces rather useless as they look the same regardless of where you aim the flash head, you’re just wasting a lot more battery power and slowing your flash’s recycling time.

Go ahead and compare the images with the Omnibounce and Lightsphere, the differences aren’t as dramatic as using a bare flash aimed at different bounced surfaces. The reason is, when using any on-cam light diffuser, you’re still using a lot of frontal, on-axis light.

With careful angling of a bare flash, you can get LARGE eye catchlights and nice, soft, wrap-around light without spending an extra buck for your flash.


Image 13 - Flash Aimed High and Behind Left Shoulder of Photographer

Take a look at Image 13, the catchlights are large, the light is very soft with very gradual transition towards the left cheek and ear. Note that there are no objectionable flash shadow either, and our subject doesn’t have that annoying small white dot at the tip of his nose and annoying chin shadow that are visible in almost all our previous examples (except Images 6 and 10).

What on-cam modifier or diffuser was used? NONE.

The flash was aimed above and behind my left shoulder and fired towards the wall and ceiling behind me. Our main light is now the rear left wall and ceiling of our living room and the effective size of that light source is approximately 16 ft². That’s a whopping 2,304 in² of surface acting as my main light!!!

If I aimed the flash a little more to the left, or used our black half-snoot (credit Neil Van Niekerk for this technique) we’ll have even better shadows on the subject’s left cheek (right part of the frame) as the light is more directional and less scattered.


I have nothing against aftermarket diffusers nor people buying them, after all, it’s not my money. However, a lot of people attribute the change in light pattern or quality to the usage of these products without realizing that the main difference lies in the change of their flash head’s direction. By aiming the flash head straight-up, all these products are merely throwing fill light forward in addition to the overhead light that the flash head is producing with or without the modifier attached.

The cost of these products are quite high, and the manufacturers have the right to ask for such pricing because of their efforts in R&D as well as marketing, but what you, as a consumer and photographer, should understand are how these things work in the first place and whether or not you can replicate the same (if not, better) results without spending a lot more for these cumbersome addition to your flash guns.

So which works? Depends on what you’re after, if you’re just after scattering light all around, then all of them do. If you want directional light that won’t give you flat, frontal light, then almost none of them will give you pleasing results.

That’s the truth and here on iPhotocourse, we want you to learn to look beyond marketing claims.

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