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Looking for a flash diffuser I stumbled upon this: Polaroid Universal Flash Diffuser

The link is to an Amazon page where you can choose from a wide range of shapes and types, but for the purpose of keeping this question focused I wanted to only consider two.

What difference to our photos does it make to use either a an octagonal diffuser or a square diffuser, and are there any particular use cases for either?


Bonus kudos for a more detailed explanation of how other shapes impact the effect of the flash!

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Also related: photo.stackexchange.com/questions/52887/… –  James Snell Jul 25 at 11:41
    
I checked that one out @JamesSnell, but I'm interested specifically in the shape. –  CLockeWork Jul 25 at 11:48

3 Answers 3

up vote 5 down vote accepted

The difference the diffuser shape makes is mainly the shape of the catchlights.

I.e - shoot a person with a square diffuser, you'll get a square catchlight in their eye. Shoot them with something round, the catchlight will be round, which arguably may look more natural. On the other hand, square catchlight can look like a window, which is also neat.

There's a section in this article on Adorama that shows the difference pretty well, specifically with this image: enter image description here

On a general note about diffusing, those small on-flash diffusers don't do too much to diffuse though unfortunately. Of course it's better than nothing but you won't get anywhere near soft light if you're shooting people. Shooting small objects though it can be useful and actually better than a very large diffuser, since that'll soften the light too much and almost erase any visible shadows for a small object.

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Thanks Jan, exactly what I need to know plus a useful fact :D –  CLockeWork Jul 25 at 11:44
    
Most welcome, thanks for the votes. –  Jan 'Saffi' Stekelgunsson Jul 31 at 12:05

The point of a diffuser is to create light that comes from a larger area and is more spread out than what the bare flash produces. Theoretically, its shape influences the distribution of the light as well, but due to the spreading-out effect, light basically goes from every point on the diffuser's surface in all directions. Which means that in practice, a square vs. an octagon will not make a noticable difference (except in highlights, where the subject directly reflects the light source). Especially since the corners of the square one will get less light from the flash in the first place.

What matters most is the size of the diffuser, its distance from the flash, and its practical usability - things like the mechanism for affixing it to the flash.

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The one's I'm looking are attached to flash by elastic. What kind of impact would that have? –  CLockeWork Jul 25 at 11:46
    
@CLockeWork: It might not always hold perfectly when you're moving around. But that's what customer reviews are for. –  Michael Borgwardt Jul 25 at 13:07
    
True enough, thanks :) –  CLockeWork Jul 25 at 14:01

The primary difference in diffuser shapes is in the shape of any specular reflections in the image, for example the catchlights in the subjects eyes.

Octagonal diffusers produce highlights which look more rounded and therefore more natural and less obtrusive.

However, in some cases hard edged highlights are required for a certain look, you see this a lot with product photography, particularly that of the Apple corporation!

"IPhone 5C" by Justin14 - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

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Interesting; I always thought that light/shadow was photoshoped! –  CLockeWork Jul 25 at 11:47
    
It's not photoshopped, the whole image is a render. It's simulating the effect referenced here though. –  Rich Bradshaw Jul 25 at 12:09
    
That image may be rendered, but not all Apple product photos are: theverge.com/2013/5/8/4311868/… –  Matt Grum Jul 25 at 12:19

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