Why use shortest sync speed rather than a slower shutter speed?

dubcat

dubcat

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Amir
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If flash is the dominant light source, e.g. say it is 3 stops or more than ambient light, what is the point of pushing the shutter speed up to the fastest sync speed available? Why not choose a slower shutter speed allowing the flashes to work less hard? In this situation the flash is going to freeze motion anyway right?

e.g. Why choose a shutter speed of 200 rather than 100 or even 50?
 
Oh that makes sense. Sorry - trying to think about more than one thing is too hard for me :) So the choice of shutter speed at or below sync speed is basically arbitrary until the speed becomes so slow that there is enough time for ambient light to have an impact?
 
From things that a lot of people have said to me, I think that most people just don't understand that the only real function of the shutter is to be open when the flash fires - many of them seem to think that it affects the exposure in some way.

You're right. When shooting indoors with low ambient light levels, there is absolutely no point in using a shutter speed shorter than 1/125th sec. At speeds longer than that, there is a possibility of the ambient affecting the shot in a few unusual situations, e.g. daylight coming through a window, very bright modelling lamps when the flash head is near to the subject.

Mind you, in the bad old days focal plane shutters had a max synch speed of just 1/30th, and we always managed.
 
Perfect! Thanks :) I guess the easy way to prove that ambient light is not having an impact is to simply shoot a shot without any flash and ensure that you get a 100% black shot! :)
 
You could equally argue, if shutter speed up to max x-sync makes no difference to the exposure, why not shoot at max?

However, the quoted max x-sync speed refers to using speedlites that have short or very short flash durations. Handbook for Canon 5D2 actually says use 1/60sec or 1/30sec for "large studio flash units" to make sure the whole of the flash pulse is captured.

That's a bit extreme, and my default is 1/125sec as Garry suggests. I've never had any problem with that, with any kind of flash at all. But if you do have a very long duration flash head (and there are some, like Lastolite's amazingly sluggish Lumin8) there is a just noticeable shading around the bottom of the frame if you shoot at max x-sync with some cameras (depends how tight the actual x-sync rating is).

Also, some radio triggers introduce a fractional delay and you can get a dark band appearing at the bottom of the frame at the max x-sync speed. With modern cameras, 1/125sec covers all eventualities.
 
HoppyUK said:
You could equally argue, if shutter speed up to max x-sync makes no difference to the exposure, why not shoot at max?
Click to expand...

With leaf shutters built into lenses which most medium format cameras have, it is normal to use high shutter speeds as these shutters will synchronise with flash at all speeds.

It's only outside or inside with bright lighting that you will want to set a suitable shutter speed to get a good balance of ambient and flash lighting.

The reason focal plane shutters have a maximum sync. speed quoted is because that is the fastest speed at which the whole of the sensor or film is uncovered by the shutter curtains. At faster speeds the second curtain will start to close before the first curtain has finished opening. As the speed increases, it starts its travel earlier until at the highest speed, just a small traveling strip of light exposes the sensor or film.

If you shoot a flash only shot with a speed higher than the camera's maximum flash speed, you will get a black band across the image.


Steve.
 
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Garry Edwards said:
From things that a lot of people have said to me, I think that most people just don't understand that the only real function of the shutter is to be open when the flash fires - many of them seem to think that it affects the exposure in some way.
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For someone so experienced and knowledgeable I’m surprised at how poor this statement is.

When shooting in an environment where there is ambient light available and you are also using flash then the shutter speed and aperture are equally important. It is very wrong to suggest that all the shutter has to do is open. In this situation where there is ambient and flash light then the shutter speed controls the amount of ambient light entering the lens and the aperture affects the amount of flash light entering the lens (as well as the level of ambient light and the depth of field).

In a studio environment where you are working with flash lighting only then settings of 1/60th at f8 would get you the same exposure as 1/125th at f8 however when out in the real world where there is ambient light then an aperture of f8 would affect how much the very quick duration of flash light exposes the image and the shutter speed controls the ambient. So 1/60th would let in twice as much ambient light as 1/125th.
 
-Rob- said:
For someone so experienced and knowledgeable I’m surprised at how poor this statement is.

When shooting in an environment where there is ambient light available and you are also using flash then the shutter speed and aperture are equally important. It is very wrong to suggest that all the shutter has to do is open. In this situation where there is ambient and flash light then the shutter speed controls the amount of ambient light entering the lens and the aperture affects the amount of flash light entering the lens (as well as the level of ambient light and the depth of field).

In a studio environment where you are working with flash lighting only then settings of 1/60th at f8 would get you the same exposure as 1/125th at f8 however when out in the real world where there is ambient light then an aperture of f8 would affect how much the very quick duration of flash light exposes the image and the shutter speed controls the ambient. So 1/60th would let in twice as much ambient light as 1/125th.
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Rob
It's clear from reading the thread that Garry was talking about only the flash exposure.
 
There is always ambient light at some level when i shoot (room lights, etc) - the reason i mentioned that the flash light was dominant by 3 stops or more was to eliminate ambient light from the equation. Sorry if i was not completely clear.
 
-Rob- said:
It's also clear (to me) from the OP that they asked the question about shooting in a situation where there is flash and ambient light to be considered so I saw Garry's post as very confusing/misleading to someone that doesn't understand.
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I answered the question, and try to be succint.
Obviously ANY level of ambient light has a theoretical effect, and equally obviously when flash exposures are combined with daylight exposures, then that effect becomes practical as well as theoretical.

Perhaps I should have given a much longer explanation, in fact perhaps I should have written a book about it... Oh, hang on a minute, I have written a book about it - so if you want a very detailed explanation that covers every possibility, buy the book:)

If anyone is worried about possible contamination from ambient light, just set up the shot with the shutter speed/aperture combination that you're planning to use with the flash and take a test shot without the flash. That will tell you whether there is a problem or not.
 
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