Trey Ratcliff talks about how he gets photos without people in them

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In his video, Trey shows one of the techniques he uses when there are lots of people and he doesn't want them to appear in the photo. I've tried something similar and it really works.  Take a look at the video here. You may find an increase in "Noise" with these long exposures. You'll have to deal with that in post.

In the photo above, I actually wanted the people.  I think it adds to the excitement of the location.