The nuts and bolts of off-camera flash

Just to make it easier for reference, I’m collecting all 4 parts of this piece together into one post before they get lost in the black pit of the “blog archive”!

PART 1 – Intro/basics

PART 2 – Manual flash

PART 3 – TTL wireless

PART 4 – Syncing/sync speed

So there you have it!  all the nitty gritty of off camera flash in one convenient package for your bookmarking convenience 🙂

The Nuts and Bolts of Off Camera Flash – Part 3, TTL wireless

CLICK HERE FOR PART 1- Basics

CLICK HERE FOR PART 2 – Manual Flash

Ok, now that we’ve talked about getting your strobe off camera, and triggering it manually, lets talk about the other “main” option for firing it – wireless TTL

In simplest terms it means that your camera and flash “talk” to each other to automatically determine the proper exposure.  Just like the automatic metering modes for your camera (where it calculates the exposure based on reading the light of the scene) TTL flash does the same thing – lets your camera automatically calculate the amount of flash needed for a scene.  Generally the way this is done is that the camera fires a “pre flash”, a small burst from the flash to “test” the scene, which is read and exposure/amount of flash is calculated.  The shutter is then opened, and the actual exposure is taken with the flash firing to the degree calculated by the pre-flash.

Now bear in mind that although wireless TTL and manual flash both achieve the same end result (firing your flash off camera, they are very different beasts.  Remember all that hardware we talked about for firing your flash manually?  (pocketwizards, cables, ebay triggers etc…?)  None of that will work for TTL.  Remember that all those devices are doing is carying a “FIRE” pulse to the flash.  they are essentially “dumb”.   TTL requires actual communication between the flash and the camera.

The good news is that if you have a modern dslr and “system” strobe (meaning the manufacturere’s dedicated strobe, designed to work with TTL)  you may already be able to do wireless TTL with no additional hardware.

Now as mentioned, modern TTL implementations rely on a preflash to meter the scene, and the the flash fires based on this meting calculation.  When the flash is on-camera this is no problem, since the strobe can “talk” to the camera directly (notice the several other pins on the foot of the “system” flash vs. the manual flash?  those are used for ttl communication)

<- TTL flash foot vs. manual flash foot.

But what happens when we want to take that TTL flash off camera?  Somehow it needs to be able to recieve the metering information to “know” how to set it’s output for the exposure.  Most current camera makers solve this problem by using an optical TTL signal.  In other words, the camera/master uses a series of quick flashes that are “read” by an optical sensor on the strobe, and these tell it the metering/TTL information.  There is a “master” device, usually an onboard flash either built-in or mounted on camera which sends out the preflash communication, and the wireless flashes are the “slaves” that read the flashed signal given by the master and pop accordingly.

This method of communication is actually quite sophisticated.  Most of the current optical TTL systems can control multiple groups of flashes at independent power levels, and power output/ EV compensation can be set directly from the master (it transmits this information to the slaves).  In practice what this means is that you can set flash power level & ratios directly from your camera/master device without having to adjust each strobe manually.  Cool huh?

In terms of a master: Nikon, Olympus, and Pentax all have DSLRS that allow you to use the built-in (pop-up) flash as a master to control slaved TTL strobes, while canon requires you to actually have a strobe mounted on camera (or use the ST-E2, which is a dedicated wireless TTL controller) to control your slaves.   I’m not going to go into the actual setup and configuration of each TTL system, as that is *way* beyond the scope of this article.  Suffice to say, RTFM 🙂  In short, you switch your strobes into slave mode, your camera/master into “master” mode, and then are able to control your slaves from the master, setting ratios and such.  The master tells the slaves how to fire based on the preflash metering information, and Bob’s your uncle…

Now given the advantages of wireless TTL flash, you might be wondering why not always use it and forget about manual?  There are a couple of big downsides to TTL flash:

1 – it is proprietary. The pre-flash ttl protocols that each manufacturer uses to communicate between master and slaves are specific to that manufacture.  What this means is that you are locked in to using that manufacturer’s strobes that support it’s TTL protocols.  Want to use 3rd party? out of luck.  want to mix in studio lights? No dice…  (actually it is possible to do this, but we’re not going to talk about it here 🙂

2 – (and this is the biggee) line of sight (LOS) is required. Since the TTL information is sent optically (by superqick pre-flashes), the camera and strobe have to be able to “see” each other in order to “talk”.   In practice what this means is that you are limited as to where you can place your strobes off camera (since they have to be able to see the signal flashes) and also that these systems become, shall we say, less than reliable in bright ambient conditions or outdoors (since all the ambient light makes it difficult for the sensor to see the signal flashes).   This is a generally “game breaking” limitation for working pros in the field who need to be able to depend on their strobes to fire every time without fail?  (remember I said that rock-solid reliablility is the reason to pay $200 for a pocketwizard over a $20 ebay trigger?  same deal here.)

Enter the RadioPopper…

Much in the same way that a pocket wizard or ebay trigger acts as a “bridge” for the “fire” signal in manual flash setups, the radiopoppers act as a “Bridge” for the visual signal flashes required for TTL communication.

Basically they way radiopoppers work is you have a transmitter and receiver – the transmitter sits on top of your “commander” unit (either an on camera strobe or dedicated commander unit – st-e2 or su800) and “reads” the magnetic pulses created by the master’s signal flashes (apparently the signal flashes generate a magnetic field around the flash head as well).  The transmitter then sends this information via an RF signal, much like a PW (but in this case it is more than just a “fire” signal) to the receiver which has a tiny little LED light inside.  The reciever decodes the RF signal and uses it’s little IR LED to replicate the same signal flashes right in front of the sensor, giving the strobe the exact same optical TTL signal it would have gotten from the commander unit regardless of how far away it is (or around a corner etc…)!  It’s a rather clever setup.  The fact that it is simply tranlating the signals from the master means that it is not system specific – the RadioPoppers will work with both Canon and Nikon’s TTL systems (other systems are not “officially”  supported, but reports have confirmed at least basic functionality with Sony/Minolta and Pentax).

The beauty of Radiopoppers is that since they are essentially just an RF “bridge” for the system’s optical TTL signal, they support all the TTL functionality that the system does, inclusing HSS (High Speed Sync), without the limitations of line-of-sight or range that the optical system imposes.    I personally have a set of radiopoppers, and after using them for a few weeks, I have no idea how I ever managed without them.   Even when I am setting my flash power manually, the ability to do wireless HSS without the limitations of optical TTL is a beautiful thing.  Plus for a lazy slob like me, the ability to control levels/set ratios without walking to each flash is just worth it’s weight in gold.   I really can’t say enough great things about the radiopoppers.

The only downside to the radiopoppers is that they only do TTL.  In other words if you just want to trigger manual flashes or studio lights, the radiopoppers are useless (since they are just an RF bridge for the optical signal) you still need pocketwizards or the like.

Anyway, in conclusion, while off camera TTL is somewhat complex, the hardware needed for it is quite simple – in general it is just a matter of having a compatible master and slave unit – either the onboard flash or hotshoe mounted, along with line of sight to trigger the slave flashes.  If youare limited by the shortcomigns of the optical signaling system, Radiopoppers will give you RF reliablility/capablility while preserving the TTL functionality of the system, so in essence you have a choice between using the built in capabilities of the system or radiopoppers, and that’s about it!  Wireless TTL is a very useful feature (albeit with drawbacks) and in my opinion belongs in the repitoire of every strobist! (If it’s good enough for Joe McNally, it’s good enough for me 🙂

Stay tuned for the 4th and final part, when we talk about the little oddities of flash triggering, notably sync speed and ways to “cheat” it!

Continue to part 4 – syncing and misc. topics!

The Nuts and Bolts of off-camera flash – Part 1, Basics

So unless you’ve been living under a rock (photographically speaking) for the past year or so, you’ve probably heard of David Hobby, AKA The Strobist.  The strobist blog has been singlehandedly responsible for introducing a whole new wave of photographers to the beauty and mystery that is: off camera lighting!

The problem is – a lot of this stuff is still confusing.  Heck, I didn’t “get it” the first time I read through lighting101.  Or the second.  Or probably not even the third.  And a lot of the time, the problem isn’t conceptual, it often comes down to the “nuts-and-bolts” issues – eg, things like “what works with what”, “how do I connect x to y” and “why is there a black bar across my image when I use my flash off camera but not on camera”

What I am going to do in this series of articles, is break down, step-by-step the various hardware and methods needed to get your flash off camera and firing properly.  We’re not going to worry about lighting theory or anything like that – just the “nuts and bolts”.

  • In par 1 (here) we’re going to talk about the basics of how a flash works, and the different modes you can use it in.
  • In part 2 we will discuss options for manual triggering.
  • In part 3 we will discuss wireless ttl flash
  • and finally in part 4 we will deal with some miscellaneous topics, such as x-sync, HSS, rear-curtain sync etc…

So without further ado, lets talk about getting your flash out of the hotshoe and into the wild where it belongs!

Now first of all it is important to understand how a flash actually fires.  In actuality it is quite simple – if you look at the bottom of your flash (or “foot”) there is an electrical contact, the center pin.  If you have a newer “system” flash, it may have other pins as well, but they all have the one center pin.  Now if you look at the inner sides of the foot, they are also metal.   When a connection is made between the center pin and the sides of the foot, the flash fires.

That’s it.  You could make your flash fire by connecting these two contacts with a paperclip even. (although I wouldn’t recommend it and am not responsible if you electrocute yourself trying it!)

So in essence, triggering your flash is simply a matter of making the connection that allows it to release it’s charge as a burst of light.   The catch, of course, is *how we make this connection*.

Now let’s step back for a minute.  Before we think about triggering the flash lets look at the primary “modes” of the flash.   In essence, a flash only has 1 adjustment – power.  In other words, “how much light does it put out when it pops”.  However, there are several ways of *calculating* how much power is needed or desired for a particular situation.

  1. manual.  Back in the day, all flashes were manual, meaning they were essentially “dumb”  *you* set the power output by hand, based on what you calculated was needed.
  2. auto.  auto flash is basically a way that the flash itself measures the amount of light needed based on settings you input.  We will not talk be talking much about auto-flash since I believe manual or ttl are more useful 99% of the time.
  3. TTL.  Stands for “Through The Lens”, and is a method where the camera and flash “talk” to each other and calculate the appropriate amount of flash automatically based on the camera settings and a meter reading.

For purposes of this discussion, we are just going to talk about manual and ttl flash, as I think they are the most useful.    The point to all this is that, despite having the same outcome (firing the flash) the *methods* for triggering your flash are very different depending on whether you will be using manual mode or TTL.

In part 2 we will talk about options for triggering your flash in manual mode, what kind of hardware you need for each, and pros and cons for each option.  Stay tuned!

UPDATE:  part 2 is now up – find it here