If you're at all like me, you have gear that offers more than one choice for a key light (main light) modifier. I'm talking, of course, about when you're using strobes.
There's all kinds of potential candidates for the key modifier job and different situations and/or environments might dictate which modifier makes most sense. Other times, the "look" you're going after pushes you towards one modifier over another. Still other times, it's simply about which modifier you feel like using for a variety of reasons-- including what might be the quickest and easiest to set up. (The last one often dictates my key light modifier choice... but I'm
Lighting manufacturers offer a big array of modifiers to choose from: From umbrellas to soft boxes to panels and scrims to ring flashes to beauty dishes and more. Of course, some people like to shoot bare bulb. Bare-bulbers, I'm thinking, might be photographers who are also nudists.
I'm not going to attempt to write about all the reasons you might choose one modifier over another. That's a subject that sometimes takes up a chapter or more in photography books. But I will mention a few things that might push you towards choosing one key modifier over another, especially if you're a pretty girl shooter.
When shooting beauty and a lot of glamour, soft is good. Soft lighting isn't always the way to go, depending on the look you want to give your images but, often enough, soft is the way many glam and beauty shooters go. Leastwise, for their key or main light. (Note: Just to make sure we're all on the same page, when I say "soft" I'm speaking to the quality of the light. I'm not talking about focus.)
If you're thinking soft, you're probably thinking bigger modifiers. You know, like BIG soft boxes and BIG umbrellas and BIG whatever you're using. The bigger the better if soft is your goal. When it comes to lighting, soft lighting, size does matter. If you don't have BIG, you should be thinking of moving your key modifier in as close to your model as possible. That way, the source becomes bigger by virtue of its proximity to the subject. It's kind of like those words printed on your car's side-view mirror about things appearing closer than they appear... sort of, in a round-about way. Or maybe not.
My two, fave, key modifiers, not necessarily in order of preference, are Octos and beauty dishes. I own a Mola 33.5" "Euro" and a 5' Photoflex Octodome. Through one of my regular clients, I also have regular access to a 7' Photoflex Octodome.
There are some distinguishable differences between the Mola dish and an Octo. Most notably, the Mola provides more "wrap-around" light while the Octos seem to produce less of that quality. I've never shot with a big parabolic but I'm thinking it also provides a lot of wrap-around light quality.
Many shooters use grids on their big light sources. Grids provide more control, i.e., less spread to the light. They also effect wrap-around quality as they make the light more directional. Grids, I should add, don't particularly reduce the soft qualities of a big light source. I mean, they might to some extent, but you'd probably need scientific instruments to measure a grid's effect on softness.
I should also note that I have a white, silk, baffle for my Mola but I almost never use it. The baffle, to my eye, alters the effect of the dish, turning it into something that more closely resembles a soft box in its light quality. If I want the look of a soft box I'll use a soft box.
I hear a lot of shooters say they're in search of their "style." Style comprises many elements, from composition to color and exposure, to so many other things. Lighting certainly is one of those elements. In fact, its a BIG element when defining one's style.
I suggest people experiment with using a variety of key modifiers until they find one or two that, for the most part, makes them happy. That's not to say that once you've found some favorites you should ignore all the other possibilities. Variety is the spice of life. Changing up your choices in this matter shows a greater range of lighting acumen. You probably don't want to appear static or stagnant in your lighting approaches in spite of your desires to create a definable and recognizable personal style.
The pretty girl at the top is Kat from some time ago. It was shot in a studio in North Hollywood, CA. I lit Kat with my 5' Photoflex Octo for a main, set slightly to my right at about the same height as me. (I'm 5'10") To camera-left, at about a 45 behind the model, I set a medium Chimera strip box on a stand with the top of the box about even with the top of the model's head. To camera-right, I used a small, silver-lined umbrella, boomed up fairly high also coming from behind Kat. I snapped the image with a Canon 85mm f/1.8 prime on my 5D.