F/1.0

Note: this is the final part of a 4 part series -
PART 1 - basics

PART 2 - manual flash

PART 3 - TTL wireless

Let’s talk about sync speed.
Sync speed is probably the most misunderstood topic for folks starting out with off-camera lighting, and for good reason.  There is a ton of seemingly contradictory information out there, misinformation, disinformation and downright wrong information… but really it’s not all that complicated, so let’s break it down.   First off to understand “sync speed” we must first understand how an SLR shutter works.  SLRs (whether digital or film) all (generally) use a type of shutter known as a “focal plane” shutter -

Obviously the job of a shutter is to expose your film or sensor for a prescribed period of time (usually less than a second).  The way a focal plane shutter work is by using 2 “curtains” that travel across the film plane.  The first (or “leading”) curtain starts by moving outward, exposing the film plane, and when it is done the “trailing” curtain follows it closing off the exposure.  Now what happens when the shutter speed gets faster than a certain point is that the 2nd curtain starts its travel before the first curtain has cleared the film plane.  In other words, the film/sensor is *never completely exposed* as a whole.   As the exposure get faster and faster, there is an increasingly narrow “slit” created by the two curtains that kind of “paints” itself across the film.  While this poses no problem for a shot using a continuous light source, for flash this is quite problematic.  Since normally the actual duration of the flash burst is much faster than the actual exposure, if one of the curtains is in front of the film plane when the flash “pops” it will partially block the light, yeilding the dreaded “black bars” across part of the image.

(Ben Mathis of the Lighting-Practice blog has a great animation of this here)

So in essence when you talk about “sync speed” this is what you are referring to - the maximum shutter speed at which the film is completely exposed at a point of the exposure.

Now if you think abou thtis process, it is a actually a hard physical limit.  There is physically *no way* to change how the shutter curtains operate, or the maximum speed at which they are fully open.  In other words, when folks throw around the term “cheating” or “hacking” the sync speed, it actually has *nothing to do* with the physical x-sync per-se, which is a common point of confusion.  What they are talking about is actually different ways of manipulating the flash burst to “work around” they shutter limitation.

*of course having said that*, let me first point out the exception to the rule

Invariably, during any sync speed discussion, someone will inevitably chime in with “you must be wrong since I normally at up to 1/2000 or so all the time with flash”.    They are, in fact, correct but it is a special case - they are generally using a Nikon D70/D40 when they report this.   There is a unique feature on some Nikon DSLRs (and a few other cameras), which is that they actually don’t use a purely mechanical focal plane shutter - they use what is called a “hybrid” Electronic/mechanical shutter.   This works similarly to a regular focal plane shutter, in that there are the normal first and second curtain, however after a certain point (usually 1/60th) any exposure faster than that does *not* precipitate an increase in the physical shutter speed - the curtains still open/close at 1/60th, however the camera merely “grabs” a smaller and smaller “slice” of the exposure recorded by the CCD.  In other words, even at 1/2000, the shutter is still opening for 1/60th, and then a tiny slice of that exposure is recorded.  The practical ramifications of this is that in essence the shutter is *always*  fully open for the eposure (for all practical purposes) - you never have to worry about the curtains blocking the flash.
Now for those of us who don’t have one of these cameras, we need a different method if we want to use flash with shutter speeds higher than the sync.

The first, and most common is known as HSS (High Speed Sync), sometimes also referred to as “focal plane sync” (FP sync).  Remember that at speeds higher than the max sync speed, the shutter curtains are essentially creating a “slit” that travels across the film plane.  In HSS, the flash will “strobe”, firing a series of superfast bursts (instead of one single burst) that are timed to match up with the shutter movement, ensuring that the whole frame is exposed uniformly as the “shutter slit” passes across each part.  HSS works great, although there are 2 major downsides.

1) it is proprietary - because the flash needs to “talk” to the camera in order to ensure that it’s pulses are timed properly with the shutter movement, HSS is limited to the manufacturers TTL capable flash units, so manual flashes and studio strobes are out :-).  This also means that triggering solutions like cables/pocketwizards/any manual triggering will *not* work (remember they only provide a “dumb” fire signal, no communication which is needed for HSS).  This means you are limited to using the manufacturers wireless ttl triggering if you want HSS off camera (and Radiopoppers potentially) with the associated drawbacks)

2) because the flash has to fire a bunch of little “pulses” across the entire exposure from a single charge of the capacitor (as opposed to one big burst), the flash output is *drastically* decreased.  HSS really eats the output of your flash (hence Dave Hobby & Joe McNally’s desert shoot using *7* SB800s

That being said, if you are using system flashes with something like radiopoppers (or in an indoor/studio situation) HSS is probably the easiest way to sync past the max sync speed of your camera.

Another (and much less optimal) method actually involves turning the flash into a conitnuous light source!!

Consider:  even though the flash may seem to be an instantaneous burst, it still takes time for the burst to occur.  (this depends on the flash and the power, but often in the range of 1/4000-1/7000 second) that is the time that the flash is physically “on” putting out light.  Now consider if your shutter speed is faster than that, the sensor “sees” the flash output for its entire exposure!  in essence the flash has become a continuous light source as far as the camera is conernced.  Now this isn’t a particularly flexible solution (requires very specific parameters from both camera and flash in order to work), however in the right circumstances in a pinch it will do…  (one thing to remember if you are doing this as that as a “continuous light” the flash contribution to the exposure is now affected by shutter speed just as ambient is!)

I personally shoot with a Canon 5d which has a max sync of 1/200. for faster, I generally use HSS with radiopoppers, or in a pinch the Canon G9 has a hybrid electro-mechanical shutter as described above (similar to the D70/D40) which allows syncing up to 1/2000 or 1/2500 pretty reliably.   Between those 2 methods, I cover all my bases pretty well.

Anyway, that about wraps it up for “the nuts and bolts of off-camera flash”.  I hope this series has been informative, and I may add/refine/clarify it as time goes on

-Ed Z

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!

After eagerly following the saga of the Radiopoppers, from their vaporware inception to their current production I finally have a pair in my grubby little hands.  Oh happy day

(you want a review?  Here’s my review: radiopoppers rock my face 437 ways from sunday.  Get some.)

Now I got them to use with my newly acquired Canon 5D kit, but as it happens I still have some Pentax gear as well.  Officially Radiopoppers do not support Pentax PTTL, but I figured what harm could it do to test.

I mounted the P1 receiver on a Pentax 540FGZ flash.  Flash was set to wireless pttl slave (SL1).  Note that on the 540 the sensor you need to position the bead over is the lower right corner of the face, as you look at the flash *not* the round part in the middle (that’s just the AF assist light)

I set the K10d onboard flash to wireless controller mode, and covered the actual flash itself to ensure no light was coming out and triggering a false positive.   I fired off a few shots, and sure enough no slave firing - good!

Then I turned on the P1 transmitter, and placed it on top of the k10d.  The popup actually seemed to support it’s weight, and the transmitters fit rested nicely against the top of the eyecup.  I think it would be mountable with a little piece of velcro on top of the pop up flash!

The big moment - I fired a shot and sure enough, the slave popped!  Exposure looked correct too (roughly, just by glancing at the LCD.   I ran through a few apertures from 2.8 to 8 and the flash exposure seemed to remain consistent, indicating that metering info is working!  I could visibly see the difference in light output as the flash popped at different apertures as well.
So it seems that at least the basic functionality of the P1s works with Pentax’s PTTL wireless sytem.  it actually fires the flash, and ttl metering appears to work.   Bear in mind however, that this is far from a scientific test and YMMV.  Further testing will be needed

So I’ve done the cardboard snoot thing.  It’s cheap.  It works.  but I find they don’t last too long trashing around in a camera bag.   I really like the idea of a flexible snoot like the Honl speedsnoot, so I figured I’d try to make my own…

A quick trip down to Perl (art supply store) yielded the required materials.  2 9″x12″ sheets of “foamies” craft foam (it’s a thin, neoprene like foam material - flexible yet rigid enough to hold it’s shape) one white, one black and 4′ of velcro “wrap” (the velcro that has hooks on one side and loops on the other, so it can stick to itself if you wrap it around something)  The neat thing about the foamies sheets is that you can get them either plain or with one side covered in adhesive.   I opted for a plain black and an adhesive-backed white sheet.

total cost for materials: about $5 (the velcro was $3 and I think the foamies sheets were .59 each)

Once at home, I simply peeled the backing off the white adhesive side, and laid the black sheet on top.  Pressing firmly secured the 2 together.  They can bend and flex together without wrinkling or buckling.

I then cut 2 velcro wraps long enough to wrap around the flash head and secure it tightly.

TaDa!  instant snoot - total time to construct: about 15-30 seconds

the best part about this snoot is that it is adjustable.  For a normal throw, wrap it into a cylinder shape, and secure each end with a wrap.   If you want a tighter throw, wrap it into a cone shape.  You can get a very tight dot of light this way.

Another added benifit is that it can be used as a bounce card - simple wrap one end around the flash head pointing up, and leave the other end free.  presto bounce card.

For five dollars and a minute of work, this is something that will have a permanent place in my camera bag!