Freezing Subject During a Long Exposure

I'm trying to experiment with new photography techniques
I've been wanting to do this many times but never knew how to do it properly...

I am trying to do a long exposure photo (anythimg from a few seconds to a few minutes) but also having a subject in the foreground that is sharp, even though it would normally be blurry.
I'm pretty sure I would have to do some sort of stacking technique. But how do I do it?

I have two examples below. These are fairly basic ones, but I have other ideas that are more complicated.


Example 1:
It's night. You're on a rooftop in the middle of a city (Toronto). The background is a long exposure of fireworks going off (4-6 sec).
In the foreground, you are standing there watching the fireworks.

Example 2:
Day time. Standing on a bridge above a waterfall, its a long exposure of the waterfall and the clouds, but you are standing perfectly still (20+ sec)
*Didn't do it in this photo as I didn't get my ND filters yet.

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At night flash would be the easiest solution. Simply pop a flash off on the foreground subject, assuming they aren't illuminated with the same light as the background. For long exposures during the day simply have them stand still. If all you're looking for is the smooth water effect you don't need such a long exposure anyway. 1-2 seconds should do it.

For example, these were done at about 1.5 seconds with an ND filter and we just took several images until one came out.

IMAGE LINK: https://flic.kr/p/VnEY​mW

IMAGE LINK: https://flic.kr/p/UZFn​uR

For something with 2 seconds, that will work, but what if I want something that is a lot longer?

Another example is when they do photography of the milky way and have someone standing there in a silhouette.

Heya,

Instead of trying to do a single long exposure, just do shorter exposures and median stack them. You'll get the same look as a long exposure on things that are moving, but you get the benefit of a short exposure for things you want sharp.

At night, or in the dark, flash is the fastest/easiest way to get a sharp foreground during a long exposure.

Very best,

Michael Frymus wrote in post #18401385
For something with 2 seconds, that will work, but what if I want something that is a lot longer?

Another example is when they do photography of the milky way and have someone standing there in a silhouette.

You have two options.... in camera or in post.

For in camera it would be hard from someone to stand still long enough. You can use a flash to illuminate/freeze them, but will probably get a bit of image blur. Another option is to have them stand out of frame then towards the end of the exposure quickly step into place and you pop the flash.

In Post is going to be easier to get right as you can take the image of the foreground/subject at night but using flash. Then shoot the long exposure background and mask in the foreground.