Why use an ND filter instead of exposure compensation for long exposures?
Asked 7/29/2010
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I want to shoot long exposures without overexposing, such as blurring water or other movement in bright light. A camera shop employee told me I don’t need a neutral density (ND) filter and could just use exposure compensation instead. I understand exposure compensation changes the camera’s chosen exposure, but I’m confused how that would replace an ND filter. What’s the difference, and when would each be used?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
16y ago
2 Answers
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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.
Originally by user10. Source · Licensed CC BY-SA 4.0
user10
16y ago
0
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They are not the same tool.
Exposure compensation tells the camera’s autoexposure system to make the photo brighter or darker than its meter suggests. It changes the chosen exposure settings, but it does not reduce the amount of light entering the lens.
An ND filter physically cuts the light coming into the lens. That lets you use a slower shutter speed or a wider aperture while keeping overall brightness under control.
For long-exposure effects in bright conditions, an ND filter is what you want. Example: if you want to blur a waterfall in daylight, the scene may simply be too bright to use a very slow shutter speed unless you reduce the incoming light with an ND filter.
You can also lengthen exposure somewhat by using lower ISO or a smaller aperture, but those have limits. Exposure compensation is still useful for telling the camera to bias exposure up or down in tricky bright or dark scenes; it doesn’t replace an ND filter for creative long exposures.
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