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

Jul 222008

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!

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part 3 coming soon!

Jul 172008

been swamped with works/other commitments this week…

“The Nuts and Bolts of Off Camera Flash – part 3″ is still in the works, I’ve got it started, should have it up by the weekend at the latest!

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From Miami Beach

Jul 122008

Had a wonderful vacation, some well needed downtime/R&R.  Lots of beach/eating/sleeping and not much else :-)   Not a lot of photography either, but a few interesting shots.  First were the *enormous* iguanas that were roaming the pool area by my family’s condo.  Seriously these things were huge… just kind of strolling around like they owned the place

A quick shot from the balcony of the hotel we went to for the evening of the 4th…

(this was shot at iso3200… I am absolutely floored by how clean and detailed the 5d is at 3200.  it is light years ahead of any crop-sensor camera I have used)

Finally one evening we had a spectacular lightning storm… the view over the ocean and the bay was fantastic as we watched the lighting move across into downtown Miami

(yes the second one is a bit blurry as I didn’t have a tripod, but the bolt was so cool it was hard to pass up)

Finally a few random snaps from here and there (along with the above, couldn’t figure out how to separate them out!)

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on vacation…

Jul 052008

just a quick post… on vacation right now in Miami Beach visiting family.  Minimalist camera gear – 5d, 24-105, 50/1.8 and the G9 for snapshots :-)

Just a few snapshots – no cable to upload them, but we saw the biggest iguanas I’ve ever seen in my life.  Seriously these things were huge – had to be about 5′ head to tail.  Just strolling around the pool at my relatives condo… Got a few shots with the G9.  what a trip.   

back this coming Wednesday, a real post when I get back!

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Shoot fireworks like a pro! (repost)

Jul 032008

REPOST FROM 6/28/07:

Philly Fireworks #1

Independence Day is coming up, and that means fireworks shows! Now admit it – we’ve all been guilty (at one point or another) of whipping out a little pocket camera and snapping away at the fireworks, handheld, in P mode, probably with the dinky little on-camera flash going too. Yeah, I’ve done it too…

BUT…

with a little effort and a bit of technical know-how you can go from blurry, underexposed, globs-of-color-on-film shots to beautiful, crisp, rainbow bursts that will be the envy of your friends and neighbors! (grin)

(note: a lot of the techniques here are similar to the ones in my article on photographing lightning, so you may want to read that as well (LINK -opens in new window))

First things first:

GEAR:
most of this will be assuming you are using an slr/dslr. You can shoot fireworks with a pocket digicam, but it is harder. If you have one with manual controls, most of this info will apply, but pocket cams have never been known for good long/low light exposures so YMMV.

you will need:
1. a camera (duh). at least something that lets you control the aperture and has a “bulb” mode (meaning the shutter stays open as long as the button is held).
2. a tripod. we’re talking exposures of several seconds, it is impossible to hold the camera steady. Tripod is a must (the sturdier the better to cut down on “mirror slap”)
3. a cable release. used for bulb mode. Note that most wireless remotes will *not* do “bulb”, only set exposures. There may be some out there that do, but most likely you will need a *corded* remote release.

Now, on to the specifics:

TECHNIQUE:
first, set up your gear. make sure the tripod will not be disturbed/bumped during the exposures. Set up the camera on the tripod, attach the cable release. Frame the anticipated “action” area.
Before the show starts, put your camera in Aperture priority mode and take a few “test” shots to determine a good exposure, (I prefer slightly on the dark side). I like to adjust it to an aperture that will give me a decently exposed image at a shutter speed of about 2-4 seconds (since this is usually about how long I open the shutter with the release.) this isn’t an exact science, it’s just to get a rough estimate the the aperture needed for your approximate exposure time. Since the actual bursts of light will expose regardless, we are basically just calibrating the exposure for the ambient light here. Once you are comfortable with the exposure, leave the aperture set as it, and switch into M (fully manual) mode. Turn the shutter speed all the way down until it goes into “bulb” mode. Now you can manually control your shutter – when you press the button down on the cable release, the shutter will open, and stay open until you let go of the button. This way you can exactly control when the exposure stops and starts.
note: make sure you camera is set to manual focus, else you will lose shots while it “hunts” for a focus lock. Most likely focus will be set to infinity, but if you are really close/have a long lens you might need to adjust. Regardless, get it set and leave it.

There is a “rhythm” to photographing fireworks, once you get the feel for it, it’s pretty easy to “anticipate” the exposures. You can usually hear the rocket going up, a second or two before it bursts. This is when I like to start the exposure. Hear the rocket – CLICK – burst – wait a second or two for the “trails” of the burst to expose – release shutter. That’s basically it! I find most of my exposures are in the 3-5 second range. As the show goes on you will probably adjust your aperture, or even set a “preset” exposure as you find the “pattern” of the show. Either way, you still generally want to be starting your exposure right as the rocket goes up before it bursts. The exception to this is when the show gets really “intense” and many rockets are going at once, it can be difficult to tell by sound alone. In these cases, hopefully you have a general idea of the exposure needed, and I will sometimes just set an “average” exposure and just keep clicking the shutter. Kind of “spray and pray”, if you will :-)

TIPS AND TRICKS:

What lens to use?
- this really depends on 2 things: how far away from the action you are, and how tightly you want to frame the shot. Farther away = longer lens, closer = wider. The examples on this page were shot with an 85mm lens (equal to 127.5mm when using a 1.5x crop camera, like most dslrs) I was about 4 blocks away, shooting from a balcony of a high rise apartment building. I like a pretty tight framing, as it allows the actual fireworks to dominate the picture, rather than extraneous elements, so I tend toward longer rather than wider.

Framing the shot / vantage point
- This is a matter of personal taste, but I like to include the surrounding scenery in my shots to give “context” to the fireworks. (As opposed to pointing the camera up an having just the bursts against an empty sky). Usually the best way to do this is to get to a high point, so you have an unobstructed view of the surrounding area. I happen to be lucky in that my apartment’s balcony looks out over the Philadelphia Art Museum (where the fireworks show occurs), So I’ve got a great vantage point without leaving the home. But even if you don’t you can probably find something. If you live in an urban area, many high-rises have roof decks that make great spots. Tops of parking garages are also good. If you’re in a rural area, this might not be as much of an issue, since there is probably more space, and less “stuff” to get in the way of the shot, but a high vantage point is still good.

- The clearest shots often come at the beginning of the show, and after pauses in the shooting (of fireworks that is, not photos!) this is because the accumulated smoke will either not be too bad yet, or have had some time to dissipate (respectively).

-Speaking of smoke; if possible, is is advantageous to set up in an orientation where the wind is blowing at a 90 degree angle to your position. This way, the accumulated smoke from the rockets will blow out of the picture frame as quickly as possible, leaving less to “muddy” your shots.

Capturing multiple bursts.
- A cool trick if you are using bulb mode is to capture multiple bursts in one exposure. Basically they way you do this is to use bulb mode to keep the camera’s shutter open, expose one burst, then cover the lens with something to block out extraneous light, but *keep the shutter open* until the next burst, uncover the lens to expose the burst, re-cover it and so forth…

The trick here is to have something that will block light out of the lens, but NOT TOUCH IT, as the vibrations of bumping/touching the lens will ruin the shot. One common method is to use a black/dark colored baseball cap – the “bowl” of the cap will block light from entering the lens without touching it (this is what I do). You could also use a black piece of cloth, a black cardboard cylinder with one end capped etc…

Basically the sequence goes like this:
- As the first burst starts, expose normally using bulb, however, when the burst ends, instead of releasing the shutter, leave it open and with your other hand, cover the lens with your cap/coth/whatever, being careful not to bump/touch it.

-Wait

-As the next burst starts, remove the covering for the lens, expose the burst.

Repeat as desired (note,you may have to close down the aperture for these kinds of shots to compensate for the increase in ambient light over the length of the exposure)

Finally when you have enough bursts, release the shutter to finish the exposure.

CONCLUSION:
I hope these tips help you all get the most out of your holiday fireworks pictures. Photographing fireworks is not all that difficult once you get the hang of it, and can yield some spectacular results.

Enjoy the holiday everyone!
philly fireworks 2

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Radiopoppers working with Pentax! (preliminary testing)

Jul 022008

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 :-)

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