Why 1/200 sec for flash?

In the March 2009 issue of Digital SLR photography, when using 'studioflash', it recommends setting the camera to Manual, then setting shutter speed to flash sync speed which in my case (450d) is 1/200 secs.

What is the reason for this? I understand why you cant set shutter speed
higher than flash sync speed (shadow underneath the image) but why does it have to be exactly flash sync speed? Can I set it to a lower speed say 1/30 secs?

You can sync at lower speeds but the lower the shutter speed, the more ambient light will be let in. In a studio, the goal is usually to eliminate ambient light completely so it's logical to set the shutter speed as high as possible.

At 1/200 (or 1/250 for some models of cameras) the focal plane shutter curtains are FULLY OPEN across the entire frame area, so that when the flash goes off it emits light which records over the full frame. At faster shutter speeds, the shutter is a slit which exposes only a part of the frame at a time, leading to black bands where the shutter is open but the flash has already completed its illumination!

Shutter speed can be SLOWER, but when the modelling lights are incandescent they throw off the daylight color balance emitted by the flash tube.

While I'm no expert in studio lighting, when you've got 3 or 4 strobes going in a typical studio with exact ratios, you'd want to kill whatever ambient light so you can just control the strobes without having to worry about any other light source.

You can slow down the shutter. Many sports shooters do this and use the flash to freeze the action. Be very aware of this when you do it though as other issues can be encountered as a result. The most common is over-exposure of your subject. This is seen when using say AV mode, the camera exposes for your subject and then the flash is added to the mix and you have too much light. Manual is best in my opinion as you can then expose for the background and use the flash to illuminate your subject.

SYS wrote in post #7956609
While I'm no expert in studio lighting, when you've got 3 or 4 strobes going in a typical studio with exact ratios, you'd want to kill whatever ambient light so you can just control the strobes without having to worry about any other light source.

True Soo Young but in most cases ambient light is studio settings is rarely an issue. The studio is a much more controlled environment and a common experiment done in the studio is to set up a light and take a test shot at the correct exposure using the common shutter sync speed with strobes of 1/125s.

Then take the same test shot at 1/60s, then 1/30s, then 1/15s. The shot doesn't change.

Do the same experiment outdoors with huge amounts of ambient contribution and the shot changes drastically.

Hermes wrote in post #7956482
You can sync at lower speeds but the lower the shutter speed, the more ambient light will be let in. In a studio, the goal is usually to eliminate ambient light completely so it's logical to set the shutter speed as high as possible.

I think that explains it!

Wilt wrote in post #7956583
Shutter speed can be SLOWER, but when the modelling lights are incandescent they throw off the daylight color balance emitted by the flash tube.

Question answered, thanks Wilt.

SYS wrote in post #7956609
While I'm no expert in studio lighting, when you've got 3 or 4 strobes going in a typical studio with exact ratios, you'd want to kill whatever ambient light so you can just control the strobes without having to worry about any other light source.

Thanks SYS. Loved your AA battery test!

Familiaphoto wrote in post #7956626
You can slow down the shutter. Many sports shooters do this and use the flash to freeze the action. Be very aware of this when you do it though as other issues can be encountered as a result. The most common is over-exposure of your subject. This is seen when using say AV mode, the camera exposes for your subject and then the flash is added to the mix and you have too much light. Manual is best in my opinion as you can then expose for the background and use the flash to illuminate your subject.

Understood, I'll watch out for that.

TMR Design wrote in post #7956659
take a test shot at the correct exposure using the common shutter sync speed with strobes of 1/125s.

What do you mean by that. Is that the same as 'max flash sync speed'? Or is 1/125 a standard shutter speed for studio work?

purpletiger wrote in post #7961217
What do you mean by that. Is that the same as 'max flash sync speed'? Or is 1/125 a standard shutter speed for studio work?

1/30 - to whatever the max speed sync works in the studio...
and there would be no ambient light in the studio...studio is dark...

Rey.dos wrote in post #7961290
1/30 - to whatever the max speed sync works in the studio...
and there would be no ambient light in the studio...studio is dark...

Not if it needs to pass health and safety checks it isn't.

The trick is to block out all daylight and make sure the ambient light in the room is low-powered artificial lighting which can easily be killed with any reasonable shutter speed. At ISO100, it's very difficult to get the light from a few incandescent bulbs illuminating the working parts of the room to show up in an exposure - you really have to be trying.

Hermes wrote in post #7961799
Not if it needs to pass health and safety checks it isn't.

The trick is to block out all daylight and make sure the ambient light in the room is low-powered artificial lighting which can easily be killed with any reasonable shutter speed. At ISO100, it's very difficult to get the light from a few incandescent bulbs illuminating the working parts of the room to show up in an exposure - you really have to be trying.

the only available light in the studio when i shoot are the strobe lights...
nothing else...and your light is your shutter speed...

Rey.dos wrote in post #7963707
the only available light in the studio when i shoot are the strobe lights...
nothing else...and your light is your shutter speed...

If you're shooting from home and working alone that's fair enough but like I said, in a professional studio where you'll often have models, photographers' assistants, clients, make-up artists, hair stylists, wardrobe assistants, e.t.c. all doing their work, needing to walk around and stepping into the set to reposition lights, fix stray hairs, crumpled outfits, e.t.c. you cannot have a completely dark room with just the strobe modelling lights illuminating it. It's dangerous and will probably fall foul of health & safety regulations in your part of the world.

Sorry to go a bit off-topic but this is important - don't wait until someone trips over a wire or knocks themself out on a boom arm because they couldn't see properly before you adopt proper safety practices.