Diffuser or Flash

Started 4 months ago | Questions thread
Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 17,907
Hard vs. soft lighting

Jcbailey wrote:

So I went ahead and purchased a diffuser. Specifically this one


CZQC Diffuser Cover 1Set 3 Color 3 in 1 Pop-Up Flash Diffuser Cover with Bracket for DSLR Cameras Flash Bounce Diffuser Cover https://www.amazon.com/dp/B097MRDFHP/ref=cm_sw_r_cp_api_glt_fabc_9M254W15BC84ZE2X29V0

As others mentioned, this won't be very effective at actually diffusing light unless you are near your subject, like doing a head shot up close.

Since I’m not ready to use flash (external) is this a good second option for low light? I will be using the white one.

I know there are some defenitions on google about a diffuser and flash but what is a diffuser like in the real world. How will this help me

As mentioned, this probably won't help.

Let's consider two kinds of ideal light sources, a point source and an infinite diffuse source.

A point source is just a geometric point emitting light. Light travels in straight lines from this light source to the subject, and anything that blocks the light will be in shadow. This is considered hard light or harsh lighting: the edges of the shadows will be crisp and any skin imperfections will be obvious. Light intensity fall-off from a point source follows the "inverse square law" so that a subject double the distance from the light source has ¼ the light intensity illumining it, so this is very strong light fall-off.

An infinite diffuse source is a uniformly lit plane of infinite extent—another idealization of course—and will illuminate to some degree nearly an entire subject, with the light "wrapping around" the subject. There are few harsh shadows, and skin is rendered softly minimizing the visual effect of imperfections. An interesting property of such a light source is that light intensity does not change at all with distance. An object twice as far away will still be lit with the same intensity.

A flash under most circumstances will approximate a point source of light. It generates harsh shadows and its light falls off according to the inverse square law.

An overcast sky, or a blue sky from the shade, approximates an infinite diffuse source of light. The light is soft and diffuse, the intensity does not change if the subject is near or far, and lighting "wraps around" the subject.

Now suppose you have a flash diffuser. If your subject is really close to it, say, within a distance that is roughly half the width of the diffuser or closer, it will mostly act like an infinite diffuse source, and it will have the nice properties of such. But the farther away you get from such a diffuser, the more the light source acts as a point source, with all of the properties we find with those, with the exception that the light intensity is much less, since most of the light is diffused away in a wide angle rather than just being projected forward. You'll still get a nice diffused look when the subject's distance is about equal to the width of the diffuser, and this effect will quickly drop off with distance.

Your diffuser is oblong in shape, and I estimate that it is at most 4 or 5 inches high and 7 inches wide, so your diffuse subject lighting distance is very limited, at best somewhere between 4 and 7 inches away from the surface of the diffuser. You'll get *some* effect farther away, but go far enough away—like a full length portrait— you'll be left again with what's effectively a point source of light, but much dimmer than the bare flash. This might be useful for a headshot taken at close distance, or maybe for close up photography of small objects.

Pro flash diffusers, flash umbrellas, and flash soft boxes typically are three feet in diameter or larger, and are used as close as possible to the subject; where too close is only when you can see the diffuser in the photo—remember that large diffuse light sources do not change intensity with distance.

The orange diffuser would be useful indoors with incandescent lamps or other dim household lighting with a low color temperature. The blue diffuser would work in full shade or in scenes illuminated by dusk skies. But they make gels for this purpose, which filter out the light appropriately but do not diffuse.

This might help:


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