Exposure Too Long?

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Today’s Question: I’m planning to purchase a solid neutral density filter, and I’m not sure how strong a filter I should get. Is there such thing as a long exposure that is too long?

Tim’s Quick Answer: It is most certainly possible to have an exposure that is too long in terms of the effect created in the photo. As a result, it is important to be thoughtful about the strength you might need in a solid neutral density filter. As a very general rule I recommend a six-stop filter as a good place to start, but the best option depends on the nature of your photography as well as your personal preferences.

More Detail: When you use a long exposure for a photo, any motion within the scene will be rendered with a blur effect. For example, flowing water will take on a very smooth and silky appearance rather than potentially having more texture and detail.

One of the mistakes I sometimes see photographers making is to assume that if a long exposure is good, that an extremely long exposure is better. That is not always the case.

To be sure, there isn’t a single “right” decision here. In many respects a very long exposure can be just as pleasing as (or even more pleasing than) an exposure that isn’t quite as long. But more often than not, when comparing a moderately long exposure with an extremely long exposure, I tend to favor the exposure with the duration that wasn’t quite as long.

With an extremely long exposure, significant detail may be lost in areas where there was movement in the frame. In some cases subject matter within the frame might disappear altogether. Sometimes these are good things, but often they are not.

The optimal exposure time will vary based on the circumstances within the scene you’re photographing, as well as your own personal preferences. There is quite simply no replacement for experimentation and evaluation. Take a variety of exposures with different durations and see what you like.

For daylight conditions I will periodically use a very strong ten-stop neutral density filter. For more typical scenarios I will use a neutral density filter that is no stronger than six stops. And in some cases I will raise the ISO setting (or open the lens aperture) in order to shorten the exposure a bit more than the filter would typically call for.

The filter I’ve been making the most of recently is a six-stop neutral density filter from B+W Filters, which you can find here:

https://amzn.to/2RV99u2