off camera flash question, white wall became black background in photo

[minn]

It's the inverse square law! Basically as something moves away from the flash it needs greater and greater power. If you put the subject very close to the flash so that you only need a very low power and move the flash an subject away from the wall, then the light "falls off" and doesn't expose the wall. Also, snoots and scrims can help to accomplish this.

Thank you, Sir, this is very precise explanation, which I understood easily ^_*

 

[jake337]

While there are ways to make your white wall black the easiest way would be purchasing a black background.

 

[Village Idiot]

It's the inverse square law! Basically as something moves away from the flash it needs greater and greater power. If you put the subject very close to the flash so that you only need a very low power and move the flash an subject away from the wall, then the light "falls off" and doesn't expose the wall. Also, snoots and scrims can help to accomplish this.

Thank you, Sir, this is very precise explanation, which I understood easily ^_*

Unfortunately, the images on this page are gone as the photographer moved to a new server. I believe he is going to redo them though. It's the third part of a series for white seamless backgrounds. This one is how to turn the white to black and had an excellent image portraying the inverse square law that makes it completely easy to understand.

This is from a tutorial site, so I hope it's not breaking any rules but:

The inverse square law states that when you double the distance, you need four times the light.

Say you're at 1' from a flash that only has one power setting and you're properly exposed. If you move 2 feet away, you'll need 4 of those flashes. If you move to 4 feet away from the original spot, you'll need 16 flashes. 8', 64 flashes.

So with this, as you have the subject properly lit with a flash and a wall 8' away from the subject, it will appear much darker than the subject itself. This works with everything. Where it gets really tricky is when you start mixing and matching different lights at different angles and powers. It's an important thing to learn though. If you have a person 1' away from a flash an properly exposed, a 2nd person 2' away from that flash will appear four times as dark. If you want to light two subjects that aren't right next to each other, you pull the flash farther away from the first subject and turn the power up to accommodate so that the light fall off is so little that there's not a noticeable difference. There are a ton of tutorials out there.

 

[minn]

WOW, Kommander, never thought it can be quantified as such, this definitely will serve a good guideline in setup the lightings. thank you so much, and I will visit the link you recommended

It's the inverse square law! Basically as something moves away from the flash it needs greater and greater power. If you put the subject very close to the flash so that you only need a very low power and move the flash an subject away from the wall, then the light "falls off" and doesn't expose the wall. Also, snoots and scrims can help to accomplish this.

Thank you, Sir, this is very precise explanation, which I understood easily ^_*

Unfortunately, the images on this page are gone as the photographer moved to a new server. I believe he is going to redo them though. It's the third part of a series for white seamless backgrounds. This one is how to turn the white to black and had an excellent image portraying the inverse square law that makes it completely easy to understand.

This is from a tutorial site, so I hope it's not breaking any rules but:

The inverse square law states that when you double the distance, you need four times the light.

Say you're at 1' from a flash that only has one power setting and you're properly exposed. If you move 2 feet away, you'll need 4 of those flashes. If you move to 4 feet away from the original spot, you'll need 16 flashes. 8', 64 flashes.

So with this, as you have the subject properly lit with a flash and a wall 8' away from the subject, it will appear much darker than the subject itself. This works with everything. Where it gets really tricky is when you start mixing and matching different lights at different angles and powers. It's an important thing to learn though. If you have a person 1' away from a flash an properly exposed, a 2nd person 2' away from that flash will appear four times as dark. If you want to light two subjects that aren't right next to each other, you pull the flash farther away from the first subject and turn the power up to accommodate so that the light fall off is so little that there's not a noticeable difference. There are a ton of tutorials out there.

 

[astroNikon]

Your photo was taken at f/32.
You simply did this style for a Black background - long explanation here ==> The Invisible Black Backdrop - Photography Technique - Glyn Dewis

It's a simple technique but at small apertures your introduce a lot of aberrations (which most people won't see) from the light squeezing through such a small size aperture.

 

[minn]

Thank you, astroNikon, for pinpointing the image aberrations, which I didn't notice. I went through the content in below link, really appreciate the very detailed explanation. actually I've ordered a grid last Sunday, that was just before I sign in this forum.

the point I am trying to make is the image I posted was taken using bare speedlight, and this is the exact technique I have been searching for answers here. so far, the inverse square law seems dictating well the techniques. I tried a few times these days, it works pretty well except I need to figure out the hard light problem, I still assume this could be achieved by using a bare flash ... ...

Your photo was taken at f/32.
You simply did this style for a Black background - long explanation here ==> The Invisible Black Backdrop - Photography Technique - Glyn Dewis

It's a simple technique but at small apertures your introduce a lot of aberrations (which most people won't see) from the light squeezing through such a small size aperture.

 

[Braineack]

the point I am trying to make is the image I posted was taken using bare speedlight, and this is the exact technique I have been searching for answers here. so far, the inverse square law seems dictating well the techniques. I tried a few times these days, it works pretty well except I need to figure out the hard light problem, I still assume this could be achieved by using a bare flash ...

Still not quite sure what you're asking or looking help for...

 

[astroNikon]

The first photo was
Camera: Nikon D700
Lens: 0 mm f/0 (in other words, unknown)
Shot at 24 mm (35mm film equiv: same)
Exposure: Auto exposure, Aperture-priority AE, 1/10 sec, f/2.8, ISO 2500


The second photo with the black background
Camera: Nikon D700
Lens: 0 mm f/0 (in other words, unknown)
Shot at 24 mm (35mm film equiv: same)
Exposure: Manual exposure, 1/125 sec, f/32, ISO 200


Thus from f/2.8 to f/32 with flash is talked about in the link I provided.

I also see a 24mm lens was used.
Have to be careful with another distortion using a wide angle lens at close distances. ==> http://gizmodo.com/5857279/this-is-how-lenses-beautify-or-uglify-your-pretty-face

 

[wfooshee]

Your statements in post 3 are wrong, and a common misconception. "Shutter speed controls ambient, aperture controls flash."

No, no, no, no, no!

Ambient exposure is affected by the entire exposure triangle. Flash exposure ignores shutter speed but is still affected by aperture and ISO. If you adjust aperture because your flash is too dim, you've also adjusted your ambient exposure.

People fall into "aperture adjusts flash" thinking because with a flash on manual power, you have to set a specific aperture for correct exposure. Still, you can use a different aperture by using a different flash power.

If you want to make the background disappear into black, move your subject away from the wall and place the light rather close to the subject. The light falls of by the inverse square rule, so twice the distance has 1/4 the light, 4 times the distance has 1/16 the light. Proper exposure for a closely-placed light will have very little light for the background. On the other hand, the falloff is apparent within the area you intended to light, as well, i.e. one side of the face darker than the other.

Close light should have some kind of modifier, such as softbox or reflector, to soften shadows. (Well, any light should, but close light absolutely needs this.)

 

[minn]

Thanks, astroNikon, and wfooshee

I think both of you made great points. I fully accept the correction by wfooshee

Your statements in post 3 are wrong, and a common misconception. "Shutter speed controls ambient, aperture controls flash."

No, no, no, no, no!

Ambient exposure is affected by the entire exposure triangle. Flash exposure ignores shutter speed but is still affected by aperture and ISO. If you adjust aperture because your flash is too dim, you've also adjusted your ambient exposure.

People fall into "aperture adjusts flash" thinking because with a flash on manual power, you have to set a specific aperture for correct exposure. Still, you can use a different aperture by using a different flash power.

If you want to make the background disappear into black, move your subject away from the wall and place the light rather close to the subject. The light falls of by the inverse square rule, so twice the distance has 1/4 the light, 4 times the distance has 1/16 the light. Proper exposure for a closely-placed light will have very little light for the background. On the other hand, the falloff is apparent within the area you intended to light, as well, i.e. one side of the face darker than the other.

Close light should have some kind of modifier, such as softbox or reflector, to soften shadows. (Well, any light should, but close light absolutely needs this.)

 

[mcap1972]

I would add another flash to separate the background.

 

[minn]

mcap1972, thank you very much for the advice.