Thought of the Day with Unwanted Ambient Light in Flash Photography

The other day we were discussing (in part) the subject of ambient /modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?

Cheers,

Colin

C J Southern wrote:

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?

Most people just look at the exposure meter: if it's indicating a -2
or more under-exposure, the flash will be the dominant source of light.

"C J Southern" wrote:
The other day we were discussing (in part) the subject of ambient /modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?

In many (most?) circumstance that will not indicate much, though
it tells more than looking at an exposure meter.

Specifically, "at my intended aperture" is only easy if you are
using everything in manual. That is unlikely these days, though
possible. The results from any form of automatic control will
of course cause what you see in the no-flash image to be a poor
representation of the light from flash as compared to ambient.

But even in manual, the only time it has much significance is
when the no-flash exposure is nearly *all* black. Just being
"hopelessly underexposed" is not good enough because for any
place that has *any* significant light, you do not know if the
flash will provide half that much, the same, or twice as much.

Hence the only proof positive way, is a test exposure, either to
the camera or to an exposure meter (which can measure
flash). The next best thing is experience that develops enough
skill at judging lighting setups to be able to make a good
estimate. Even then it usually just means you can get very
close on the first guess.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

"C J Southern" writes:

The other day we were discussing (in part) the subject of ambient /modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?

Yes, basically, that's a valid test.

And generally you'll find that's what you get.
--
David Dyer-Bennet, , http://www.dd-b.net/dd-b/
RKBA: http://noguns-nomoney.com/ http://www.dd-b.net/carry/
Pics: http://dd-b.lighthunters.net/ http://www.dd-b.net/dd-b/SnapshotAlbum/
Dragaera/Steven Brust: http://dragaera.info/

In article ,
"C J Southern" wrote:

The other day we were discussing (in part) the subject of ambient /modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?

Cheers,

Colin

Typically ambient light won't sneak in unless your using a
1/15th or slower shutter speed. For certain types of photo's it can be a
plus.




--
"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

greg_____photo(dot)com

"Floyd Davidson" wrote in message
...

Specifically, "at my intended aperture" is only easy if you are
using everything in manual. That is unlikely these days, though
possible. The results from any form of automatic control will
of course cause what you see in the no-flash image to be a poor
representation of the light from flash as compared to ambient.

Perhaps I'm wrong, but I would have thought that shooting manual would be
the norm for studio strobes (as opposed to E-TTL II compatible flashes), and
anything with flash that's over X-Sync speed?

The other day we were discussing (in part) the subject of ambient
/modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or
unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?


Should not have any effect. Most of you shoot a monolight with a couple
hundred watt seconds of light, maybe even 5 or 600 worth.

A 'watt second' is the equivalent of a light bulb burning for one full
second. So a 100 watts second flash is about what a 100 watt bulb would
give if you used a one second exposure. you would need 2 bulbs to get a
half second, 4 to get a 1/4 second, 8 to shoot at one eighth. and 16, well
you get the idea. So what is the wattage of your modeling light? 100,
150, 250? Lets say 250, how many stops would it underexpose if your flash
failed to fire? If its more than 3 stops then you won't have much of an
image, 2.5 stops was the max you could print with a storm of grain and color
shift.

This reply is echoed to the z-prophoto mailing list at yahoogroups.com

"C J Southern" wrote:
"Floyd Davidson" wrote:
Specifically, "at my intended aperture" is only easy if you are
using everything in manual. That is unlikely these days, though
possible. The results from any form of automatic control will
of course cause what you see in the no-flash image to be a poor
representation of the light from flash as compared to ambient.

Perhaps I'm wrong, but I would have thought that shooting manual would be
the norm for studio strobes (as opposed to E-TTL II compatible flashes), and
anything with flash that's over X-Sync speed?

Sure, but the opening sentence in the OP's query was:

"The other day we were discussing (in part) the subject of
ambient /modelling light - and the effect it might have on a
photo that's (it's desired to have) exposed with
flash/strobes only."

And the rest of his discussion mentioned only "ambient" and
"flash", hence it is doubtful that his question was about studio
work (which is precisely the "though possible" in my response),
as opposed to recognition that it would be a similar problem.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

"zeitgeist" wrote:
The other day we were discussing (in part) the subject of ambient /modelling
light - and the effect it might have on a photo that's (it's desired to
have) exposed with flash/strobes only.

Thinking about it last night - if I want to see how much ambient or unwanted
light is sneaking in, is it a valid technique to simply fire off a shot at
my intended aperture & shutter speed with the flashes turned off, and "see
what develops" - with a black or hopelessly underexposed image indicating
that the ambient light is playing an insignificant part of the exposure?


Should not have any effect. Most of you shoot a monolight with a couple
hundred watt seconds of light, maybe even 5 or 600 worth.

A 'watt second' is the equivalent of a light bulb burning for one full
second. So a 100 watts second flash is about what a 100 watt bulb would
give if you used a one second exposure. you would need 2 bulbs to get a
half second, 4 to get a 1/4 second, 8 to shoot at one eighth. and 16, well
you get the idea. So what is the wattage of your modeling light? 100,
150, 250? Lets say 250, how many stops would it underexpose if your flash
failed to fire? If its more than 3 stops then you won't have much of an
image, 2.5 stops was the max you could print with a storm of grain and color
shift.

That is true, and a good discussion. But it needs to be clear
that it discusses a *modelling light* (co-located with the
strobe) only. Other ambient light, coming from light source in
different directions than the strobe, cannot be evaluated in the
same way because the intensity will vary in a different manner
(e.g., shadows will be in different locations) than the strobe.

And example would be bright sunlight coming through a window to
the left of a posed subject, with for example two
strobe/modelling lights providing the main illumination from the
front and right of the subject. (Or replace the "sunlight" with
a relatively bright flourescent fixture with four or more tubes
in it, to get a really disgusting variation! :-)

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

"Floyd Davidson" wrote in message
...

And the rest of his discussion mentioned only "ambient" and
"flash", hence it is doubtful that his question was about studio
work (which is precisely the "though possible" in my response),
as opposed to recognition that it would be a similar problem.

The OP was me - and I was thinking of indoor work at the time. You're
right - I did leave a few too many doors open in asking the question.

Cheers,

Colin