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With options like Nik’s Color Efex Pro 4 allowing me to digitally apply a Graduated Neutral Density filter, why would I choose to use a piece of equipment that I have to buy and carry around?

Related Questions:

How do I use Graduated Neutral Density filters?

What are neutral density filters and how do I use them to create long exposures in daylight?

What types of filter cannot be emulated by post-processing? -This points out that exposure time or aperture can be altered and not reproduced with software.

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There are two ways to simulate a Graduated ND filter by software and they both have different disadvantages and advantages, compared to an physical filter:

H/W Filter

  • Pro: A H/W filer gives you results immediately which you can see while you compose.
  • Con: On the other hand, the effect is fixed in gradation and shape.

Software Effect

  • Pro: Adjustable in strength, size, shape and direction.
  • Con: Cannot recover clipped details. Blown out areas wont get details with a software effect while the H/W filter would have prevented over-exposure.

Exposure Fusion / HDR

  • Pro: Completely adjustable. Can simulate any strength, shape and size of ND filter.
  • Con: Anything that moves between exposures can cause problems.
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  • Does anyone have more cons for software? I feel like that list would be large. The one given above is a big deal though. – dpollitt Oct 14 '11 at 21:39
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    Isn't that enough? I always stop when something is significant enough the a longer list does not matter. One can add: Time spent in software, cost of software and, more importantly the unknown of not seeing results in advance. – Itai Oct 15 '11 at 1:23
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    For example, clipped details may not matter in a scene with average light and lacking the extremes. So then the additional cons may be more worth considering. – dpollitt Oct 15 '11 at 3:09
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    In that case, I have no idea why you would put the GND in the first place since it gives a really artificial look in most cases. – Itai Oct 15 '11 at 3:56
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Using a hardware ND filter, you reduce the incoming light. Software does not do that.

Say you want to shoot in a bright sunny day, and want to use a slow shutter speed of 1 second to make the water "silk-like" . This is almost impossible without reducing the amount of light entering the camera using a ND filter. This is because at f/16 ISO100 the shutter will still be too fast to blur the water. In this case, without the ND filter you simply cannot take the shot.

If you are shooting at night a water fountain, you will also use a gradual ND filter. Say the water fountain is brightly lit with all kinds of colors, and the surrounding and the foreground is not as brightly lit. You want to use a large apeture, low ISO and slow shutter speed to capture both the dim foreground and the water. Without the gradual ND filter the water will be over exposed, and the details will be lost.

So these are fundamentally different approaches. When you need to reduce strength of the light source, you have to use ND filter. Software only adjusts the brightness of the photo within a small limit, and only when exposure is history.

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There is one more way: http://icelandaurora.com/blog/2010/07/20/tonys-magic-cloth-technique/

Quoting from the article:

The basic technique is to fire the shutter while covering the front of the lens with the cloth and slowly raise the cloth to reveal more of the scene. The more slowly you raise the cloth, the higher the strength of the Grad.

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    Could you summarize the article here that you linked to so we have it for reference in case that website closes down? – dpollitt Oct 16 '11 at 18:05

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