Manual or TTL flash for macro?

Having switched from a manual to a TTL flash for my bug macro work, I do really appreciate the consistency it gives me between shots. I very rarely have to seriously adjust the exposure in post — or if I do, it’s the same adjustment across a series.

Having 2nd curtain sync is great, too. I’ve definitely gotten shots with visible motion blur that are usable, even pretty good, but where I can tell that I would have junked it using 1st curtain sync. The difference is in 1st curtain sync, the flash makes the exposure and then any motion gets exposed while the shutter is still open, so the blur is actually leading the motion; in 2nd curtain sync, the motion is exposed before the flash fires, so any blur is trailing the motion, like our brains expect. The image with this post is a good example: I’ve gotten many photos of sweat bees with leading blur that would have looked fine with trailing blur.

TTL flashes can be used as manual flashes, are generally built better, and generally have a better manufacturer’s warranty if you get them new. The only real downside is the major price difference, which can be really significant when you’re comparing a $40 Yongnuo with a $280 Canon. So the benefits are real and noticeable, but whether they’re worth paying $240 for is definitely going to be an individual call.

But my real point here is that there are two things I’ve noticed lately that may not be obvious to someone considering what kind of flash to buy for shooting insects.

The first is that TTLs fire a pre-flash, which they use to gauge how much light to put out, and then the camera opens the shutter and fires the actual flash pulse. This happens nearly instantly. But some insects, like smaller flies, are actually so fast that they can be startled by the pre-flash and fly away before the actual flash fires — especially if you’re shooting with 2nd curtain sync, where there’s an extra 1/250th of a second to react in. Manual flash doesn’t have this problem.

The other gotcha is that you can’t always tell if your flash is positioned efficiently. On a manual flash, it’s obvious if the flash gets out of position, because you start underexposing; if you don’t change the setting, it’s not going to change itself just because the sensor wants more light. But that’s exactly what a TTL flash does.

You might be thinking, “and that’s why I want one”, but it’s not. You want TTL to automatically deal with changes in scene: changes in focal distance as you back away just a bit, changes in the leaves around the subject as they blow in and out of frame, changes in composition as you follow an ant across a white flower, etc. But you want to know the flash is shooting roughly where you want it, somewhere around 1/32nd to 1/8th power, to take advantage of the fastest flash pulse you can. When you start shooting at 1/4, 1/2, full power because you’re only catching the subject with the dimmer edge of the flash beam, the exposure is basically slowing down and you start recording a lot more movement. Motion blur becomes very noticeable. On top of that, the flash takes longer to recycle, and it obviously drains the batteries faster.

I get around this by checking every now and then by switching over to manual to see what power level I’m basically firing at. If you’ve been shooting with a TTL speedlight and you’ve found some of your bug shots are inexplicably blurry from time to time, this might be the problem.

Neither of those two things are deal breakers for me. In fact, I doubt they’d have affected my decision to get a TTL flash at all if I’d known, since I didn’t get it just for insects. They do affect how I use the 430EX II though, so if you’re thinking about what flash to get for this kind of photography, consider this an FYI.