Not Your Everyday Banana

by Bart Arondson

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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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4  
I really hate it when the camera shop staff think they know what you want more than you do. It wasn't Jessops was it? –  Nick Miners Jul 29 '10 at 14:45
    
No, Nick, it was Wolf camera. –  Mark Jul 29 '10 at 15:21
    
I have not had the greatest experience with Wolf camera. We used to have several around Denver, Colorado...however they have diminished over the last few years. Their service, breadth of knowledge, and diversity of products has never been particularly stellar, so it is not surprising you had a confusing experience there. –  jrista Jul 30 '10 at 0:16
    
Ah - just noticed you're in the States, so you won't have Jessops (luckily). Sounds like Wolf are the US equivalent! –  Nick Miners Jul 30 '10 at 9:34
    
Some Wolf camera shops are better than others ... in some cases they appear to have been real, higher end, camera shops that got bought out by Wolf and/or Ritz camera. In other cases they are just 1 hour photo processors that also sell cameras. –  david Jul 30 '10 at 18:23
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4 Answers 4

up vote 29 down vote accepted

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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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). –  Eruditass Jul 29 '10 at 17:18
    
I'm fairly sure it should be "An ND filter" –  tolomea Jul 29 '10 at 23:23
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@tolomea: Depends on how you read an acronym. If you read ND as 'Enn Dee`, then "An ND filter" would be appropriate. However, if you read ND as the words it represents, "A neutral density filter", then "A ND filter" is more appropriate. Its difficult to properly articulate acronyms, and neither way is correct for every reader. Some readers will read it one way, others will read it the alternative way...both are valid. –  jrista Jul 30 '10 at 0:19
    
I actually agree with @tolomea; when speaking I would spontaneously say "An ND filter". –  Fredrik Mörk Jul 30 '10 at 8:34
    
@jrista - I think the proper rule is to determine if the starting sound of an acronym as spelled leads with a vowel or not, and use "an" accordingly. So the subquestion here is really "Is ND an acronym, or just an abbreviation for the web" - and I think enough products are branded as ND that it can be called an acronym. +1 for Fred's answer tho :) –  reuscam Jul 30 '10 at 13:50
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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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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). –  Imre Sep 12 '12 at 6:23
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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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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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Yeah, that's kind of what I thought also ... thanks for confirming it. –  Mark Jul 29 '10 at 14:48
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