dragging the shutter...can I?

[john_pyle1]

I have been studying this on the net for about an hour and a half and just don't seem to get

it. Can someone explain it to me? I have a Canon 20d with 580 speedlite, 17-40 f4 lens,

24-70 2.8, and 70-200mm 2.8...all canon lenses. I really want to be able to learn this

technique and something is just not registering with me. I am shooting a casual wedding sat

night and would love to nail this before then (this is my first wedding) Thanks!

[picturesque]

What have you read? Have you been to planetneil.com--the section on on-camera flash?

 

Basically, you use the flash to freeze motion, since the duration of a flash burst is very short--about 1/200th and shorter--most of the time much, much shorter. And since flash exposure is determined by aperture, you use it to control flash exposure and use the shutter speed to control how much of the ambient light you "let into" the exposure to "burn in" some background detail. Keeping that in mind, you realize that if the subject receives a good and correct "dose" of flash, he or she will be frozen, even if he or she is dancing frenetically. Because flash weakens the further from the flash head it goes, subjects behind your main subjects, and the background can show up as motion-blurred, including any specular light sources in the background. A good rule of thumb is to set the exposure to allow for correct flash for your subject (aperture) and then to allow for at least 2 stops underexposure for the ambient (shutter speed). Example. Walk into the reception. Meter the ambient, using the f stop you want to use to control flash. Set your camera for that f stop and then set your shutter speed at least 2 stops faster than what you metered. Sometimes you need to go 3 or 4 stops faster--it depends on the effect you are after. Be careful if your subject is against a bright window or bright area, since they will have motion blur lines around them, or ghosting. Also if the subject is lit by flash but part of him or her is shaded by something--the shaded part will show motion blur.

[picturesque]

Also, this is where you can ignore the handholding guideline. Because the flash freezes your subject with it's short duration, you can use a 1/15th shutter speed with your 80mm lens, assuming your flash can correctly illuminate your subject at the distance needed. Typical wedding reception settings I use for ISO 400 are f4, 1/30th or 1/60th or equivalent for medium illumination at night--the 1/30th being for a darker place. During the day, when the ambient illumination is brighter, it could be f4 at 1/125th or even 1/250th if, for instance, the place is lit by daylight through a huge picture window. You can, of course, vary the shutter speeds for different effects.

[joename]

I've never heard it called "dragging the shutter" but basically it's

fill-flash. With the 20D and 580ex this will rock. Use aperture

priority (usually 5.6 or so is good), have the flash set on E-TTL,

and dial down (the flash only - great feature on the 580ex) about 2/3

of a stop. Set the metering on the camera for averaging (blank

square), and you're good to go. If you find the exposures too long,

and causing blurriness in the background, then up the ISO from 100 to

200, 400, or even 800. This should work flawlessly.

[shiver_me_timbrrrre]

What Nadine wrote is correct. You expose for flash and then drag the shutter to expose ambient light. Remember that flash exposure is dependent only on aperture and not shutter speed.

 

If you have second curtain sync on your camera, you may want to use that instead so that motion trails from dragging the shutter seem to come from behind your subject, that is trail him or her, instead of being in front as with first curtain sync. Of course, if your subject happens to be moving backwards...

[shiver_me_timbrrrre]

I refer you to Frank Van Riper's article in the Washington Post:

 

http://www.washingtonpost.com/wp-srv/photo/essays/vanRiper/020301.htm

[michael_madio]

Nadine has it bang on. Fill flash is an entirely different animal.

[frank_kimble]

I like to think of it as taking two pics at the same time. Pic #1 is of the subject using flash, so you set the aperture to match the flash. Pic #2 is of the background, so you must use a shutter speed, generally slow, to match the aperture used in the flash pick. The flash freezes the primary subject and the slow shutter speed allows the ambient lit background to show up well in the pic. Sometimes you may actually be under-exposing the background a stop if its very dimly lit.

[twmeyer]

Rear curtain sync is fun for planned sets, but if your shutter speed is very long, it makes getting the "decisive moment" a little tricky, especially in a wedding environment... t

[shiver_me_timbrrrre]

Sure beats having the motion trails blurring your nice 'decisive moment'! As in everything else, it comes with timing which comes with practice, even for the much vaunted 'decisive moment' technique. Never heard of shutter lag? Shiv.

[blumesan]

Ordinarily when you make a flash exposure the shutter speed is set to the camera's sync speed (1/100 - 1/250 sec.) The aperture is set based on the ISO setting and the distance from the subject. The duration (strength) of the flash is usually controlled by either the flash's built in sensor or, with a dedicated flash, by thru the lens (TTL) metering. Now, since you are using a flash, it is generally the case that the ambient lighting is low to minimal. Under such circumstances the flash lit subject will be properly exposed, but all portions of the scene outside the range of the flash will be significantly underexposed.

 

Dragging the shutter, as I understand it, is simply an attempt to utilize more of the ambient light to better expose those areas outside the range of the flash, by (manually) selecting a slower shutter speed. That's it in a nutshell. This will have no effect on the flash exposure. Obviously a similar effect could be achieved by opening the aperture (relying on the TTL sensor to adjust the flash duration) but an undesired reduction of DOF may result.

 

The net effect will depend on whether the objects illuminated by the ambient light are stationary or in motion and, in some cases, by intentional movement of the camera. These effects have been well described in other posts.

 

Cheers/Mike