So, I've just come off of about 3 months of studio shoots. During that time I've gotten fairly well acquainted with basic studio lighting and using modifiers to get different looks for a photo. I thought I'd share some of my findings and summarize the lighting modifiers that I tend to use on shoots.
Click on the photos below to see a larger version.For each picture, you'll see an example of a portrait using a given light modifier. Inset in each picture is a 100% crop of the eye on the main-light side so you can observe the catch light that you get with the modifier.
The model is me. I used my new Nikon D700 camera, a Nikon 50mm f/1.4G lens along with Flashwaves wireless triggers and two Pentax AF540 flashes.
I tried to keep my camera settings at ISO200, f/8.0, 1/160th of a second shutter speed. A few times the modifier would be a half stop different than other modifiers. Since my camera was set for 1/3 stop adjustments (and I was too lazy to change it), I shot a couple of pictures at f/10 instead of f/9.5. I should have simply adjusted my ISO and kept my aperture consistent, but I'm too lazy to reshoot everything :-)
I used a main light and a fill for this. The main light is 45 degrees to camera right and the fill is 45 degrees to camera left. The lighting ratio is 3:1 on all shots except the shoot-through umbrella where I think it was 2:1. Ya, I should have reshot that...
Finally, I left the whitebalance on 'flash' so that one can observe how different modifiers give a cast to the final image. In a real shoot, I tend to match up modifiers that give a similar cast and use a graycard to set a custom whitebalance.
This isn't very scientific, but it should give you an idea of some your options if you want to explore light modifiers.
Bare Flash

Using your flash with no modifier creates a pretty harsh picture, with lots of contrast in areas where shadows fall. Note that it happens at a pretty small scale, too, so every little bump and crease will tend to show up a lot more.
The shadow falling on the curtain behind me is very hard edged. It's very noticeable in the photo and many would think it distracting.
The catchlight is small and hard.
Finally, there is quite a bit of spill from the flash - the curtain far to the right of the photo is brightly lit. You can see the light starting to fall off a bit behind my head in the photo.
Shoot-through Umbrella
A shoot-through umbrella creates quite soft light. The umbrella used is 42" and is able to create a fairly large lightsource. I picked it up used from Vistek for $20 after the salesman tried hard to convince me that hotshoe flashes were nowhere near powerful enough to use with a shoot-through umbrella. Gee, I guess this photo shouldn't exist then...
Shadow transitions are less harsh so that lines and bumps are less noticeable, giving the skin a softer look. The shadows falling on my neck (from my high collared shirt) are much less obvious than with a bare flash.
The shadow falling on the curtain is very soft and feathered and does not really detract from the photo.
The catchlight is larger and has a softer edge. Though you can kind of make up a ghostly hint of the umbrella and it's arms reflected in my eye.
Finally the spill is quite wild in this shot, even hitting the wall to camera left and helping to fill that side of my face.
Small Softbox
The softbox also creates very soft light. This particular softbox (a Photoflex Lightdome) is very small (18" x 12") but I wanted to see if even it could make a difference. I also didn't have room in the kitchen to set up my 48" x 36" softbox :-) Shadows are softer than a bare flash, but not as soft as the larger umbrella. The larger softbox makes for a softer light than the umbrella.
The shadow falling onto the curtain is fairly dark, but also quite feathered (soft) on the edge so it remains relatively undistracting.
The catchlight is fairly large (given the size of the modifier) and shows the modifier's rectagular shape. It's got fairly soft edges, though, so it's quite pleasing. The larger softbox gives a larger, less distinct catchlight.
Finally the spill remains fairly crazy and uncontrolled.
Bounce Umbrella

If you want a fairly hard look to your pictures, but still want to keep them fairly refined, use a bounce umbrella. The shadows remain fairly dark, but with somewhat featured edges. My bounce umbrella was a cheap, used unit I picked up from someone in the neighborhood for $10. I think it's supposed to be used with continuous light sources, but it works just great with my flashes.
The catchlight is also fairly large and soft, much like the shoot-through umbrella. Also light the shoot-through, you get a hint of the umbrella's structure showing relfected in the eye (though it's much less obvious).
Finally, it tends to control the spill a little better than diffusion modifiers.
Beauty Dish
The beauty dish I have is brand new and I've not used it in a shoot yet. That said, woah, I really like the look that I get from it. The shadows are deep, yet feathered. There is lots of spill and the light is a lot less harsh then with a bounce umbrella. I think it's a good middle ground between a bounce umbrella and a shoot-through.
I ordered this from
oeccamera on ebay - it was inexpensive and I simply drilled a hole in the mount area and fastened a 1/4" lighting stand stud to it with a washer and nut.
The contrast is much more muted in this shot than the bounce umbrella shot. Notice how the piping on my shirt is more stuble with the beauty dish.
Finally, the catchlight is large and hard, it stands out nicely in the picture. I like it better than the catchlight from umbrellas as there is no hint of the umbrella structure reflected in the eye.
Snoot
Blam, I'm hit with a spotlight. I had to turn down the power on the flash a bit to maintain the correct exposure, this thing really concentrates the light. The shadows are really hard and the contrast really harsh, but if that's what you need then a snoot will deliver it in spades (and using less power). While shadows cast from the subject are hard edged, the shadow around the circle of light cast by the snoot is a bit soft edged - interesting.
I ordered this from
oeccamera on ebay at the same time that I ordered the beauty dish - it was nice to save on shipping :-) Like the beauty dish, I drilled a hole in the mount area and fastened a 1/4" lighting stand stud to it with a washer and nut. It now pops onto my light stands (with umbrella brackets) quickly and easily.
The catchlight with a snoot is really hard and well defined.
Snoot with 1/8" Grid

The snoot actually came with a 1/8" grid (honeycomb) attachment that is removable. With the grid on, the flash had to be set to the same power level as with the shoot-through umbrella and the softbox. The lighting is focused by distinctly shaped - with a bright center that fades outward. The shadow around the circle of light cast by the snoot/grid combo is even more feathered that that cast by the snoot alone. Shadows cast by the subject, though, remain hard edged.
The catchlight is very similar to that of the snoot.
1/4" Speed Grid
A while ago I picked up a few modifiers from
Honl Photo. Among them I picked up both grids (or honeycombs), a 1/4" grid and a 1/8" grid. The difference is simply the size of the 'straws' that are packed inside the plastic housing. The 1/4" grid creates a fairly large spotlight effect when used 6' to 7' away from the subject. The edges of the light are nicely feathered, both on the subject and the edges of the shadow against the background. The subject shadow remains hard.
The catchlight, like other hard light sources, is small and distinct.
1/8" Speed Grid

The 1/8" grid from
Honl Photo creates a more focused spotlight effect when used 6' to 7' away from the subject. The edges of the light are very soft, both on the subject and the edges of the shadow against the background. The subject shadow remains hard. The light is a lot more focused, though, with much more noticable light falloff on the subject. If I was using a grid to light a human subject I'd use this 1/8" - I find the noticeable falloff on the subject quite pleasing.
The catchlight is small and less distinct than either the snoot or 1/4" grid.