A Flash about FlashMay 7, 2007 · psu · 6 minute read
Having buried myself in the Strobist for the last couple of weeks, I came up for air over the weekend and reflected on what I had learned. First, I learned that buying a lightstand and umbrella can be a bit stressful and complicated. But that’s not important or interesting. What is interesting to me is to compare the techniques at the Strobist with those in the excellent Bob Krist lighting book I read a few years ago. The differences can be summed up in just a few words: digital lets you see the flash.
I don’t know why it took me this long to realize this extremely important and also extremely obvious fact. It’s probably because I spent too much time writing off flash as too hard to previsualize when using film. I never felt like losing frames to my own inability to visualize the effect of flash on a picture, or the TTL flash system getting fooled by some bright reflection.
Metering for flash is different than metering for ambient light. To set exposure for ambient light, you just point the meter at the important part of the picture and twiddle the knobs until the meter says the right thing. With flash, all the light is dumped out into the world in a short, well, flash. You never actually get to look at it. Moreoever, the actual affect of the flash on the picture is primarily determined by four things:
1. The aperture setting on your camera.
2. The power output of the flash.
3. The distance from the flash to the subject being lit.
4. The ISO setting on your camera.
Note that shutter speed means nothing as far as the flash is concerned. The flash turns on and off again long before longer shutter speeds are over. Again, this is more complicated ambient exposure, where all you need to set is aperture and shutter speed (and more recently, the ISO “speed” of the digital sensor). Moreover, ambient light is observable. You can spend all day looking at it and thinking about how it will affect your pictures. Flash is over in a fleeting moment, and in the old days, you wouldn’t find out what you did wrong until the film came back.
The Krist lighting book has a few workarounds for this issue. He carries a flash meter, which perhaps helps a bit with practice. He uses polaroid backs, which seems like a lot of trouble to an enthusiastic amateur. Finally, he’s learned how the light works through years of practice, so he doesn’t have my level of flash anxiety. Krist also describes lighting setups that require huge studio heads, 1500 watt-second power-packs, all packed into multiple heavy rolling cases. It wasn’t hard to decide this was all too much work.
But, as I said above, digital has changed all this. The obvious change is that now you can see the flash. TTL flash giving you fits? Say you are in your living room with that nice 8 or 9 foot ceiling. Set your camera on manual at 1/125th and (say) F5.6 at ISO 100. Set the flash on any old power setting, point it at the ceiling and pop a picture. Look at the screen. Overexposed? Dial the flash down or close the aperture. Underexposed? Open the aperture up. Already wide open? Crank up the ISO. Presto. You have now set the perfect flash exposure for everything in the room in front of you. If you want to change the ratio of ambient to flash, you can do so by manipulating the flash power and the shutter speed. Longer shutter speeds will bring in more of the ambient. More flash power will bring in more flash. Turn the dials, pop a test, look at the screen.
In the old pre-digital days, you could do this kind of thing with a flash meter and polaroids, but it would be too time consuming and tedious for the average user. Thus, the major camera makers put more and more automatic exposure schemes into their flash systems. For me, the be-all and end-all of this evolution is the Nikon i-TTL and CLS system which combines smart metering with wireless triggering that lets me easily hold the flash off the camera. What the Strobist helped me realize is that with my magic digital box, all I really care about is the wireless trigger. I spent the whole weekend at a friend’s house with my fancy TTL flash set on manual at 1/8th power, happily flashing the room over and over again, every picture exposed perfectly. For relatively static setups and subjects that never get too far away from the lights, you just can’t beat this way of working.
The other change that digital has brought upon the world is more subtle. With a modern digital camera and a good exposure, you can take a picture at ISO 800 and print it big. Hell, even my ancient D100 could make a stunning 12x18 print at ISO 640. This simply was not possible back when slide film ruled the book and magazine industries. If you look at the pictures in Krist’s book, almost all of them are on ISO 64 or iSO 100 film. The few exceptions are the ones where he used Velvia, at ISO 50. If you look at a lot of the examples at the Strobist, he’s working at a minimum of ISO 400, and more often than not he’s up around 640 or 800. That’s two or three stops more speed, which means you can get by with four or eight times less light. This is a big deal.
My buddy’s living room from this weekend was about 20 feet long by 15 feet wide. With my camera set at ISO 400 or 800, my dinky SB-600 flash can light most of the room bounced off the ceiling or a wall with power to spare. At ISO 50 or 100, I’d drain the flash for every shot and the back of the room would be dark. In other words, the high ISO performance of the camera allows me to get good flash shots in a pretty big space. It worked well enough that what it made me want to do is get a second light so I could play around with different angles and fill the shadows a bit.
So, of course, I went out and bought a light stand and some other stuff. It’s always good when your hobbies lead to commerce.
Anyway, here’s what to remember: your digital camera lets you see the flash, giving you ultimate control. Your digital camera also lets you use small lights where you used to need big lights. This purely technical advance probably has more potential than any other for getting you better pictures. But you don’t need me to tell you that. The success of the Strobist speaks for itself.