Understanding Lighting - Strobist

[KevinStecyk]

Originally Posted by Dennis_Vied

Kevin, you were looking for a simple answer. Here's my input.

The reason he knew he was 4 stops above ambient was that he was using a shutter speed 4 stops too fast for the ambient light level. He gradually moved the shutter speed slower toward the normal exposure for the ambient light level. He metered the scene for ambient, and a certain shutter speed and aperture were called for. He set the aperture, but for test purposes, he set a shutter speed 4 stops too fast.

Excellent, thank you!

Originally Posted by Dennis_Vied

In the meantime, the flash exposure was determined by the lens aperture. So, in each exposure, the camera was close enough to be affected by the flash, but the background was not. So, in each exposure, (except for the last few with very slow shutter speeds), the camera received pretty much the same exposure, while the background exposure increased with the slower shutter speed. Therefore, the camera looks about the same while the background gets brighter, (or closer to a normal exposure).

Does this make sense?

When I look contrast the earlier shots of the camera and later shots, I do see a slight increase in brightness on the camera. So the camera does receive some additional exposure because of the increased time?

I understand the background becoming progressively lighter.

I realize I am being very detailed, probably beyond pragmatic application.

My belief is that, for all intents and purposes, if you keep the aperture the same and increase time, the subject remains at the same exposure while the background brightens.

If we take a very detailed look, would we modify the above statement to read as shown below?

If you keep the aperture the same and increase time, the subject receives a slight increase in exposure while the background brightens tremendously. That is, a three stop increase in time exposure will make a slight difference in exposure to the subject but will increase the background from almost darkness to normal light exposure.

[Dennis_Vied]

Yes. The key to understanding it is that the APERTURE creates the proper exposure for the subject (camera) AT THAT DISTANCE for THAT FLASH POWER (guide number). It doesn't affect the background because that is beyond the range of the flash at that power.

The shutter speed AND aperture determine the exposure for the scene as lighted by ambient light. Naturally, as the exposure is increased, all areas of the scene are affected, but since the flash is properly exposing the camera in each shot, the amount of exposure of the camera changes less noticeably.

That is a good demonstration, and you are quite right in trying to understand all the details, because it is a key lesson in understanding flash lighting.

[Ed Gerson]

[quote=KevinStecyk;452949]Chris and Michael,
I want to know if I missed something in the Strobist article.
--------------------------------------------------------------------

Norman lighting equipment has/had some very elementary pamphlets on fill lighting and other lighting situations published decades ago. If they're still available, you won't believe how deceptively thin and concise they are.

There's so much legitimate information out there from other manufacturers as well, resource them and learn: Photogenic, Speedotron, White Lightning, etc. - Ed

[David_Buzzard]

If the ambient light is the same on the subject on the foreground and background, then as you increase the shutter speed, the ambient light, the flash will have less affect on the subjects in the foreground. If the ambient light is less in the foreground, then the flash exposure will stay the same, while the ambient light in the background gets lighter.

For doing outside portraits with flash, you really want to find locations that without flash, the main subject would be silliouted against the background. Under trees or covered patios are prime spots. For big shoots, like Vanity Fair, they bring big canopies to set up on location to keep the ambient light off the subject, and then light the subject with strobe.

To sum up, find a covered area that is darker than your background to put your subject in, set up your light, or lights, so that the subject is properly lit, and then adjust the shutter speed until the background is properly exposed.

If you look at the archive on my blog, the entries 'Falconer', 'Stacy Kohut on the Four Cross', and 'An Inconvenient Truth', are all shot in this style. in a lot of them, if you look at the ground you can see the shade from the trees I poised them under.

David Buzzard's Technical Blog

[KevinStecyk]

Originally Posted by Dennis_Vied

Yes. The key to understanding it is that the APERTURE creates the proper exposure for the subject (camera) AT THAT DISTANCE for THAT FLASH POWER (guide number). It doesn't affect the background because that is beyond the range of the flash at that power.

The shutter speed AND aperture determine the exposure for the scene as lighted by ambient light. Naturally, as the exposure is increased, all areas of the scene are affected, but since the flash is properly exposing the camera in each shot, the amount of exposure of the camera changes less noticeably.

That is a good demonstration, and you are quite right in trying to understand all the details, because it is a key lesson in understanding flash lighting.

Thank you Dennis. Your responses are very helpful.

[KevinStecyk]

[quote=Ed Gerson;452997]

Originally Posted by KevinStecyk

Chris and Michael,
I want to know if I missed something in the Strobist article.
--------------------------------------------------------------------

Norman lighting equipment has/had some very elementary pamphlets on fill lighting and other lighting situations published decades ago. If they're still available, you won't believe how deceptively thin and concise they are.

There's so much legitimate information out there from other manufacturers as well, resource them and learn: Photogenic, Speedotron, White Lightning, etc. - Ed

Thank you Ed.

[KevinStecyk]

Originally Posted by David_Buzzard

If the ambient light is the same on the subject on the foreground and background, then as you increase the shutter speed, the ambient light, the flash will have less affect on the subjects in the foreground. If the ambient light is less in the foreground, then the flash exposure will stay the same, while the ambient light in the background gets lighter.

David, that's great information.

Originally Posted by David_Buzzard

For doing outside portraits with flash, you really want to find locations that without flash, the main subject would be silliouted against the background. Under trees or covered patios are prime spots. For big shoots, like Vanity Fair, they bring big canopies to set up on location to keep the ambient light off the subject, and then light the subject with strobe.

To sum up, find a covered area that is darker than your background to put your subject in, set up your light, or lights, so that the subject is properly lit, and then adjust the shutter speed until the background is properly exposed.

If you look at the archive on my blog, the entries 'Falconer', 'Stacy Kohut on the Four Cross', and 'An Inconvenient Truth', are all shot in this style. in a lot of them, if you look at the ground you can see the shade from the trees I poised them under.

David Buzzard's Technical Blog

I will look at those posts in your blog shortly. Your information again is helpful.

Thank you!

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