Slower Shutter Speed?

Cason · October 19, 2006

This is taken from an article I read about flash photography. The problem is a large room with a dark background even when a flash is used. You want the background to be brighter w\o blowing out the foreground subjects.

His solution was to lower the shutter speed to 1\8th or even 1\4th @ f4. He goes on to say that the slow shutter speed will still make the subject sharp. How is that possible? I'm not understanding his point. With a 50mm lens pointing at a statue, I can barely hold it at 1\50th wiithout some blurring.

What ISO do you think he uses? Or does that even matter?

UT Scott · October 19, 2006

I think what he's saying that the area is so dark that when taken at as low as 1/4 of a second there wouldnt be enough light to expose the subject, that's where the flash comes in, the flash will brighten up the subject but only for the duration of the flash, that's how it stays sharp. I'm still not sure how he expects the background to expose properly, but chances are I have no idea what I'm talking about

pathfinder · October 19, 2006

When shooting flash in manual mode ( camera and flash unit in manual ), the aperture of the camera and the flash distance to the subject determine the proper exposure for the subject.

The shutter speed then limits ( sets) the exposure for the background
( unless the shutter speed is much faster than the flash which does not happen with a normal focal plane shutter)

I make use of this when shooting with a macro lens - I can illuminate a butterfly or a spider with the flash in high speed synch in manual mode, and by using a fast shutter speed - say 1/500 or better, I can drive the background to black and eliminate the cluttered background seen in macro shooting in a garden environment.

For example f8 Manual Mode 1/125th sec - I probably should have used 1/250th for a darker background

By using a very long shutter speed - say 5 seconds, the background might go very bright but a butterfly won't hold still that long. It is all about balancing the exposure of the forground and the background, using flash for one and natural light for the other.

Montec · October 19, 2006

I think this is refered to as 'dragging the shutter'
A good reference for this can be found here
http://www.planetneil.com/faq/dragging-the-shutter.html

LiquidAir · October 19, 2006

The flash duration is much shorter than the shutter speed. Typical flash durations are 1/10000 second (this is how people stop motion on things like bullets) which considerably faster than the shutter.

You can think of a shot taken with a flash as really two images overlayed in one picture: one taken with just the flash and a very fast shutter speed, the other taken with ambient light and a slower shutter speed. It is a common practice in flash photography to try to balance the brightness of the ambient image with the flash image. You can get many different effects by controlling the relative brightness of each part.

Since the flash image is taken with an extremely fast effective shutter speed, it will never be motion blurred. Only the ambient image has a long enough exposure time to blur. In most common flash setups the flash is much closer to the subject than it is to the background which means is it much brighter on the subect. If you expose with flash a stop or two brighter than the amibent on the subject, the motion blur of the subject will not be very noticable because the flash image will be so much brigher and it will be sharp. However, in the background where the ambient is brighter than the flash, motion blur will be much more pronounced.

TenOx · October 20, 2006

Flash Duration
Duration of light output varies. It can be very short or up to say 1/200 of a second. The brighter the flash, then longer the output lasts, so if you want a very short flash duration, say short enough to freeze very rapid movement, then you need to set up the shot to allow for a smaller amount of flash output. Some good ways to do this are by using more than one flash and having them synched together and by having the flash(s) very close to the subject -- esp. good for small subjects. There are also special high output strobes ($$$) that reach their peak output faster than most units, but you also have to look at their output decay curves too, in order to determine their usefulness for a given application.

/..

Cason · October 20, 2006

What would the standard setting for the flash if it is set to manual? 1\1, 1\4, 1\8 etc? I need to research this but isn't 1\1 the big flash that sux battery up?

Slower Shutter Speed?

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