Though it fell out of use for a while, the Fresnel lens has regained popularity for portraiture work, where it can provide a sharp and impactful light quality that is still flattering on the subject's facial features. If you have not used a Fresnel before and want to learn how to employ one to create compelling portraits, check out this fantastic video tutorial that will show you everything you need to know.
Coming to you from John Gress, this helpful video tutorial will show you the ins and outs of using Fresnels for portraiture lighting. Once the go-to modifier for Hollywood, the Fresnel fell out of use in the second half of the 20th century but is enjoying a bit of a comeback. Fresnels provide a relatively hard light by collimating the beam (they have long been a staple of lighthouses), creating a powerful source that is nonetheless flattering on the subject, but that still allows for relatively sharp and deep contrasts. Because of that focused beam, a Fresnel stands up to diffusion better than other modifiers, without significant sacrifices in exposure. They are a very creative and fun modifier to work with. Check out the video above for the full rundown.
If you would like to continue learning about how to light a portrait, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"
Want a fresnel spot, but don't have the big bucks you'd need to get one?
You can make one out of a speedlight!
Get a "whole page magnifier" from an office supply store. This is generally a 9"x12" or so flexible fresnel lens, intended for magnifying a whole page of paper.
In a darkened room with a single overhead light, move the lens up and down to focus that light as a visible image on the floor. Measure the distance the lens is from the floor. That is your "focal length."
Get some white tag board or something similar, and make a pyramid-shaped tube that is the size of the speedlight on one end, spreading out to the size of the fresnel lens on the other. Connect the speedlight to the lens.
Now, you can throw a smallish spot across the room with your speedlight!
I've come across John's videos a few times and he is one of the most well spoken and talented photographers I've seen. Great information and a killer demo as well