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I was at the camera shop a few weeks ago looking for a neutral density filter, so I could play around with long exposure shots without overexposing.

The guy at the camera shop told me I didn't need a ND filter I could just use exposure compensation.

I've got a general idea of what exposure compenstation does ... but really don't understand what the guy was talking about.

Could someone elaborate?

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I disagree with the sales person; it's two completely different things.

  • Exposure compensation is used for making the image brighter or darker than what automatic exposure in the camera would make it.
  • An ND filter is used for allowing a slower shutter speed without making the image brighter.

If you would simply use exposure compensation, you would pretty soon have a situation where you blow out the highlights because there is too much light hitting the sensor.

In short, there are some different ways that you can achieve slower shutter speeds without altering the overall image brightness:

  • Use a lower ISO setting - this will allow you to also use a slower shutter speed with the same aperture without making the image brighter.
  • User a smaller aperture - this will allow you to use a slower shutter speed, but it will also increase the depth of field.
  • Use a filter that "eats" some light - This is where the ND filter comes into the picture. It blocks some light without altering the image in any other way, so you can use slower shutter speeds than what would otherwise be possible.
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    \$\begingroup\$ Another option is blending multiple shots together. My K-x has it built in, called multi-exposure, with a checkbox for Auto-EV adjustment (otherwise it will add up the exposure instead of averaging). \$\endgroup\$
    – eruditass
    Commented Jul 29, 2010 at 17:18
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I think your camera shop guy miss understood your intention.

Exposure compensation is designed to compensate for the camera's light meter over exposing for very dark compositions, and under exposing for very bright compositions. You tell the camera "For this composition, I want you to measure the light, then add (or subtract) xx stops to compensate".

ND filters reduce the amount of light entering the lens so that you are able to use a longer shutter speed, or, a wider aperture. Exposure compensation would still be used in the same fashion, to compensate for an overly dark or extremely bright situation.

They are, in this case, completely unrelated.

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  • \$\begingroup\$ Yeah, that's kind of what I thought also ... thanks for confirming it. \$\endgroup\$
    – Mark
    Commented Jul 29, 2010 at 14:48
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It's worth noting that an ND filter and setting a negative exposure compensation ARE equivalent when photographing a still-life scene, so that could explain the salesperson's comment.

That said, I don't see why you'd ever use an ND filter to shoot a scene that has no movement in it, so his/her advice is somewhat moot. It is perfect for things like allowing you to capture the blur of a waterfall on a sunny day, or trying to remove all the people from Times Square by shooting it over a long period, so the moving people disappear.

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    \$\begingroup\$ Sometimes ND filters are used for shooting still-life in bright day-light with small f-stop numbers. That way one gets the shallow depth of field and with the max shutter speed of the camera (1/8000). \$\endgroup\$
    – BiGYaN
    Commented May 25, 2015 at 17:43
  • \$\begingroup\$ ^ That's how I use the ND filter too, particular useful shooting outdoor portraits. \$\endgroup\$
    – user47015
    Commented Dec 10, 2015 at 19:58
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Using a ND filter and setting a negative exposure compensation are equivalent, but for example in broad daylight even after applying the maximum negative compensation available on a camera you can achieve only certain shutter speed without overexposure which is generally insufficient for creative effects.

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    \$\begingroup\$ Exposure compensation will result in under- or overexposure, whether you hit saturation limits or not. Using ND filter will give the metered correct exposure (mentioning "exposure compensation" implies an automatic exposure mode is used). So they are not equivalent. Rather. ND filter is equivalent with using a lower ISO (but it can be lowered only as far as the camera allows). \$\endgroup\$
    – Imre
    Commented Sep 12, 2012 at 6:23

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