So according to this article slow shutter speed blurs motion. Whereas, fast shutter speed freezes action. What constitutes fast shutter speed? How I remember it is the more the number is as in 1/xxxx, the faster the shutter speed. In other words, 1/1600th of a second is a faster shutter speed than 1/30th of a second. According to the article normally what constitutes a fast shutter speed is more than 1/500th of a second for general photography.
So I found that when I was trying to take the same vaping action by my husband in a dimly lit room, at night, my ISO had automatically changed to 800, and I found that I had to use a lower shutter speed from 1/80 - 1/40th of a second in order to properly expose the picture.
However, I always try to set my aperture at 3.5, simply because I love that slightly blurred out background feel. I used my trusty Nikon D3200 with my stock 18-55mm lens. All you professional photographers out there, if you happen to read this post and found that I could do better or that I misunderstood certain stuff, do let me know. Would love to learn! xx