Flash photography and using an ND filter

Started May 12, 2013 | Discussions thread
Sailor Blue
Sailor Blue Forum Pro • Posts: 12,403
Re: Flash photography and using an ND filter

drh681 wrote:

Fave Photog wrote:

dad_of_four wrote:

Sailor Blue wrote:

The only reasons I can see for using a ND filter with flash are:

Shooting outdoors in bright conditions, and being constrained by the x-Synch speed of your camera and your desired aperture.

That's what Sailor Blue said:

"Outdoors...the ND filter is used to reduce the ambient light exposure."

Uh... a neutral density filter would reduce the over all exposure not just the ambient.

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If you use flash from a hot-shoe flash or a studio strobe then you are making two exposures.  One exposure is an ambient light exposure.  One exposure is a flash exposure, or if outdoors it is a combination of ambient and flash.

In a studio the ambient light exposure is usually much lower than the flash exposure so it can be neglected.  The problem in the studio is usually too much strobe power even at the lowest settings, and this is when you start adding extra layers of diffuser material to the light sources to reduce their intensity.

Using flash restricts your shutter speed to a maximum of the sync speed.  If you want to use a wide aperture to give you a small depth-of-field then you can easily find your outdoor ambient lit background being overexposed.  This is when you add the ND filter to cut down the ambient light lit background exposure and crank up the power of the flash to offset the exposure reduction of the ND filter.

If you use window light as one light source indoors and add flash as the second light source then you are again looking for ways to adjust the ambient and flash exposures.  If you are unable to keep the ambient light background from being overexposed at wide apertures, chosen for a small depth-of-field, then you need to use the ND filter to reduce the ambient background exposure and up the flash power appropriately.

I hope this clears up any confusion.

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