The role shutter speed has to flash photography.

[Digital]

From what I have read, and seen on videos, shutter speed when using flash only controls the ambient light.
It seems to me in a discussion about a year ago that this was not always the case. Could someone clarify this or am I correct in my initial statement.
Thank you.


Bruce

[Manfred M]

Theoretically it is a bit of an oversimplification, but practically the statement can be viewed as being more or less correct.

The reason I suggest this is that ISO, shutter speed and aperture all have an impact on the exposure.

If you want to test this out, take a shot (in manual mode; Auto-ISO disabled) and look at the image using the settings you will be using for a flash shot. That will give you the impact of the ambient light on the image. If your screen is completely black, the influence of the ambient light is negligible. If there is some component of the image that is lit, that is the ambient light contribution to the image. Turn on the flash and there is your shot; this is the combination of both light sources.

My flash meter (Sekonic L-358) gives me a reading that tells me the percentage of the light that comes from the flash and the percentage due to ambient light. This is useful when using fill flash.

[Digital]

Thanks Manfred for the information.


Bruce

[William W]

. . . further to what Manfred wrote, I encourage to you think of any shot that uses Ambient Light and Flash Light as a 'A Two Part Composite Image' comprising the 'Ambient Exposed Image' and the 'Flash Exposed Image'.

. . . and to cast out thought processes such as of "shutter speed CONTROLS the Ambient Light".

It is really difficult to "control" light, we can modify the light falling on the scene with bounce or diffusion; expose the film or sensor for a particular duration of time - but we really don't "control".

This is one instance when I think that pedantry does assist a practical understanding - I have seen that when folk think about this situation as 'two images over-laid or mixed together', then it is a light bulb moment for them.

***

The earlier conversation to which you referred, might have included discussion about HSS (High Speed Sync) and/or using Studio Flash Heads some of which have a relatively long Flash Duration.

In these cases there are situations where choice of the Camera's Shutter Speed will have a direct effect on the (exposure of) the 'Flash Exposed Image' as well as having a direct effect on the (exposure of) the 'Ambient Exposed Image'.

***

But for most practical purposes when you are using Flash in addition to an Ambient lit Scene you are safe to choose your ISO and then I encourage you to think along these lines:

The Shutter Speed and Aperture that I choose will determine the (exposure of) the 'Ambient Exposed Image'

additionally -

The Aperture I have chosen, will then directly relate to the amount of FLASH light that I let through which will overlay onto the (exposure of) that 'Ambient Exposed Image'.

WW

[george013]

What influence can a shutter speed up to sync time, about 1/250, have on a flash time of about 1/1000?

George

[Stagecoach]

What influence can a shutter speed up to sync time, about 1/250, have on a flash time of about 1/1000?

George

Your question is ambiguous George.

do you mean;

a) do different shutter speeds up to sync speed (say 1/250) have an affect on the flash duration time?

or

b) If different shutter speeds up to sync speed (say 1/250) influence the IMAGE when a flash having a duration of about 1/1000s is used?

Are you asking a) or b)?

[pnodrog]

I think what George was getting at is that at a given flash power and provided the flash is in X sync the shutter speed has no effect on the flash component of the exposure.

[george013]

Your question is ambiguous George.

do you mean;

a) do different shutter speeds up sync speed (say 1/250) have an affect on the flash duration time?

or

b) If different shutter speeds up to sync speed (say 1/250) influence the IMAGE when a flash having a duration of about 1/1000s is used?

Are you asking a) or b)?

It was meant as a rhetorical question. You can only influence the flash exposure with the shutter speed if that shutter speed is shorter as the flash. And that is not possible, practical.

The answers of Manfred and William is more how to deal with it.

George

[Stagecoach]

It was meant as a rhetorical question. You can only influence the flash exposure with the shutter speed if that shutter speed is shorter as the flash.

Exactly, wording again.

[george013]

But with figures. So I thought it was obvious.

George

[Stagecoach]

But with figures. So I thought it was obvious.

George

I do not think it is likely to be obvious as a rhetorical question to those that are learning flash as Bruce is.

[george013]

I do not think it is likely to be obvious as a rhetorical question to those that are learning flash as Bruce is.

Wording again.

George

[Manfred M]

Wording again.

Explanations are all about the wording.

I did a lot of technical writing as part of my job, and my first question was always "who is the target audience?". I would adjust my wording / writing style depending on the audience. The general public would get one approach, technical people would get another, corporate executives would get another, etc., etc.

Writing at a level that the audience can understand (even if it is not technically perfect) is very important when communicating technical subjects.

[Black Pearl]

It was meant as a rhetorical question. You can only influence the flash exposure with the shutter speed if that shutter speed is shorter as the flash. And that is not possible, practical.

The answers of Manfred and William is more how to deal with it.

George

Really?

So if you set a shutter speed of 30 seconds it wouldn't affect the exposure? Well I suppose that is right if you were in an absolutely pitch black room but thats an odd place to be taking photographs.

[pnodrog]

Explanations are all about the wording.

I did a lot of technical writing as part of my job, and my first question was always "who is the target audience?". I would adjust my wording / writing style depending on the audience. The general public would get one approach, technical people would get another, corporate executives would get another, etc., etc.

Writing at a level that the audience can understand (even if it is not technically perfect) is very important when communicating technical subjects.

Alternative facts?...... ....Now I know who to blame.....

[Manfred M]

Alternative facts?...... ....Now I know who to blame.....

I was once at a gathering of friends and family. One of the people there was a commercial photographer who had just bought a pair of Elichrom battery powered flashes that he was planning to use for the wedding work for some effects.

He and I were discussing the decay curve of the units (effectively the t.1 characteristics). Along came another friend who is a PhD physicist and he started thinking about what was happening as the electrons were dropping out of one orbital and and dropping to a lower one and emitting a photon. A third person, who is an occasional photographer just wanted to know if the flash he bought would do what he wanted.

[pnodrog]

I was once at a gathering of friends and family. One of the people there was a commercial photographer who had just bought a pair of Elichrom battery powered flashes that he was planning to use for the wedding work for some effects.

He and I were discussing the decay curve of the units (effectively the t.1 characteristics). Along came another friend who is a PhD physicist and he started thinking about what was happening as the electrons were dropping out of one orbital and and dropping to a lower one and emitting a photon. A third person, who is an occasional photographer just wanted to know if the flash he bought would do what he wanted.

Sounds like some of the strange conversations I have had while out fishing with friends who have completely different backgrounds. (Chemistry teacher, Electronics engineer, Plumber)

[george013]

Explanations are all about the wording.

I did a lot of technical writing as part of my job, and my first question was always "who is the target audience?". I would adjust my wording / writing style depending on the audience. The general public would get one approach, technical people would get another, corporate executives would get another, etc., etc.

Writing at a level that the audience can understand (even if it is not technically perfect) is very important when communicating technical subjects.

Your first question should be "what's the question". And that's whether

shutter speed when using flash only controls the ambient light."

Not by starting your answer with

Theoretically it is a bit of an oversimplification, but practically the statement can be viewed as being more or less correct.

The reason I suggest this is that ISO, shutter speed and aperture all have an impact on the exposure.

You start to answer a not asked question, how to use it. You don't explain the relation between shutter speed and flash.

George

[george013]

Really?

So if you set a shutter speed of 30 seconds it wouldn't affect the exposure? Well I suppose that is right if you were in an absolutely pitch black room but thats an odd place to be taking photographs.

English is not my native language. But I think it's yours. Why don't you read what I wrote and qoute what I wrote correctly. And try to understand.

You can only influence the FLASH EXPOSURE with the shutter speed if that shutter speed is shorter as the flash.

George

[xpatUSA]

Theoretically it is a bit of an oversimplification, but practically the statement can be viewed as being more or less correct.

The reason I suggest this is that ISO, shutter speed and aperture all have an impact on the exposure.

May I clarify that?

Only the shutter speed and aperture directly impact the exposure of the sensor. All other forms of chicanery such as, ISO, EC, etc., affect only the combination of shutter speed and aperture, therefore ISO affects exposure indirectly.

The proof of the pudding being in that, if one sets the camera in manual at some fixed combination of shutter speed+aperture and then waggles the ISO knob around taking many shots of the same scene, the raw data (i.e. sensor exposure) will not change much, if at all.

While this is admittedly a trivial clarification and could be viewed as irrelevant, it may have some bearing on this thread's discussion.