When you choose to photograph action using flash, there are a couple points that are important and it matters not whether you are shooting front or rear curtain. If you want to shoot someone running and have them frozen amongst the blur movement, you have to do a couple things. First, the ambient light level has to allow you long shutter speeds of at least 1/15th second. Longer is better. This means shooting at dusk/dawn or low light levels. You can do some movement blurring in the sun, but you have to stop your aperture all the way down to get a long enough shutter speed to make the blur show. For example, if you camera meter says 1/125th @ f/8.5 (F/9.3245698 ?????) and you want a slow shutter speed, then you adjust to f/32 and your new shutter is around 1/10th. Perfect for some blur! But your next consideration is now that you are at f/32, what range does the flash have? Will it send enough flash to your subject for proper exposure? Most likely your subject will now need to be close to the camera and require the use of a wide angle lens.
Another important point regarding blur/flash and 2nd curtain is, for this to work you need your subject brighter, and background darker, to see the blur. If you just place your camera on Auto shooting mode and ‘flash away’ hoping for a cool blur effect, you might find it doesn’t work. It’s because your flash and ambient are at the same exposure level. You need to separate these by underexposing the ambient so that the flash puts a nice light on your subject to brighten them against the darker background. You do not want your ambient underexposed so much that you no longer see the blur and that is why I typically choose -1. For example, if my camera’s normal metering says f/11 @ ¼ second and flash on ETTL, I do one of two things. In A/Av mode I use Exposure Compensation at -1. If in Manual mode, I just change the shutter speed from ¼ to 1/8th and the camera should show a -1 underexposure. F/stop is still f/11 so flash output is not affected.
I rarely use High Speed Sync since I find setting it up to time consuming and it really only creates one effect, the blur behind the flashed subject, and I don’t find a need for that very often. But here is when you could use it. (Hypothetical) You are, for example, on the mountain, skiing, and your son is going to come down the hill and jump off a small cornice for some air. Your fastest sync speed is 1/200th on your camera and the sun is behind him, somewhat, so he is going to be backlit. You want to use a flash fill on him since you are looking at his shadow side. The sun is out and it is really bright so at 1/200th your f/stop is f/16, according to your meter. The problem with this situation is that you can’t get very close to your son’s position and your flash won’t output enough light to flash fill him at that distance using an aperture of f/16. At the distance you are from the subject, the flash will only output f/5.6 and to use that f/stop you need a shutter speed of 1/800th based on the camera’s meter. Unfortunately, your designated sync speed is 1/200th.
Now go into HSS and set a really fast shutter speed. But remember, your flash output will be really fast in HSS and for the flash to be that fast, the output will be significantly lower than normal flash shooting. This means faster flash at a weaker output level. Next, set the camera to HSS and choose a shutter of 1/3200 and the new f/stop is f/2.8. Now the flash has the ability to send enough light that distance and have a fast shutter speed to freeze action and use flash.
While I was out scouting locations for a place to shoot with my students during a Utah workshop, I discovered this rock with holes in it. I thought if I wait for dark and put a flash inside the holes, what would the result be? So I did that. I waited for it to get a little darker and then took a bunch of bracketed exposures making the rocks dark. When I had that exposure determined, I then set a flash, with a radio remote attached and a strawberry colored gel, inside the hole on the left and took the picture. Then moved the flash to the middle hole and took another, and last, the right hole. I then opened all three in PS and painted in the middle and right holes using layer masks. This is the result.
In the next photo, I wanted to light this arch with colored flash. The first thing I did was shoot just the arch with a good sky and underexposed some, meaning I waited for the sun to set. Then without moving the camera, I waited for pitch dark and then set the camera to bulb so the shutter would remain open when pressed. You need a cable release that locks and keeps the shutter open to do this. Once I was ready to flash, I hollered for my wife to remove the lens cap and I flashed the colored flash on the rocks. As soon as my wife saw the flash she put the lens cap back on the lens. When I was ready to flash again, I let her know and we flashed a couple more times. It might take some trial and error to get it right, but the results are fun.
More fun with gels and flash
For this outdoor portrait, I chose to place the subject in the shade so no sun was hitting him. I used my battery powered Norman 400B strobe, bounced it out of an umbrella, and added a warming gel to it for the golden light. Once the flash exposure was determined, I bracketed the shutter speed to make the background darker in some and lighter in others.
I also used this guy in another shot with a brick wall background. I also used the 400B flash on the left side with a small white umbrella to soften it. In Photoshop I selected him and did a Grunge effect to his skin (Google ‘Grunge Effect’) and the selected the wall separately and changed it to blue.