Tetra ROC Controller (a.k.a. Housing Sanity Check)

I'd like to understand better how the TTL works on the Tetra systems. I've never seen one of these housings as they are way beyond my pricerange.

Jeff made some very good comments in the last thread that opened my eyes to this (even if it did contain some unnecessary personal flames that obfuscated the issue--which is why I started a new thread).

Beyond that, what the D-180 does is not TTL of any kind. "Through the Lens" means just that -- the control is through the lens. The D-180 auto function requires you to set the aperture of the camera on a dial on the strobe. A light sensor in the strobe head quenches the strobe when it calculates enough light has been delivered. The auto system is completely independent of the pre-flash system. In fact, with a 5050 or later, the best approach is to put the camera in "Slave" mode and eliminate the pre-flash altogether. If you have a camera where the pre-flash cannot be disabled, the D-180's Advanced Cancel Circuit will fire a pre-flash that will "trick" the camera into firing a very weak, brief main flash, thus conserving battery life. The pre-flash system has absolutely nothing to do with the D-180's auto quenching system.  

So what is the difference between the ROC and the Ikelite TTL strobe controller? I don't know much about this, but it seems that the Tetra has the same sort of circuitry built into the housing as you get with Ikelite in a seperate box? Does this flash watcher use seperate batteries? Ikelite gets its power from the strobe.

This might be a bit better in terms of having a simpler system and maybe better light trapping but honestly I'm a bit dissapointed. The advantage of having a truly wired strobe is the reduction in heat and battery consumption of having to use the internal strobe. This way you still get the same problems with humidity and short battery life as you get with the oly housings at much more cost. In this case you can get similur TTL control by adding only $150 Ikelite controller to the PT housing cost. You still won't have the superior build/functionality etc, but the cost difference is huge.

On the other hand, you would have a big benifit by going with the ikelite housing. For 1/2 or less of the cost of the tetra you would get real wired TTL (better battery, light, and humidity control) and have the ability to add Ike's new dome port for the add on lens (a concession to the loss of external lenses with the 5060).

Am I understanding this wrong?

I'll get this technical discussion started (Sorry Dave Haas ;-)):

TTL is a term used to describe flash metering. Originally it stood for "Through the Lens" metering. As in the light meter that sets the flash power is inside the camera body, behind the lens somewhere.

So any "system" that sets the flash power based on a meter or meters inside the camera behind the lens can be called TTL.

Film camera TTL meters read the flash's reflection off of the film. Digital SLR systems read the reflection off of the camera CCD (fuji S1 and S2), read a reflection off the camera's shutter (D-TTL), or use a flash/exposure meter inside the camera's viewfinder above the mirror (i-TTL).

OK, so back to the Tetra discussion. To me, a camera does TTL strobe control if the camera uses a meter behind the lens to set the flash power. If I understand how the Tetra 5050 and 5060 work then they DO perform TTL under that definition. However, they don't pass the "flash control/power signal" to the flash through the camera's hotshoe. Instead, the signal is passed optically, from the camera's preflash and flash, to a light sensor in the housing, then through conversion circuitry electrically to the external flash - using a TTL sync cord. (the cord has a fire and quench contact).

The Coolpix 5000/Tetra5000 is different. On this camera, the flash meter is actually on the outside of the camera next to the lens. It reads the flash coming back to it, and passes the fire and quench signals to an external strobe through the camera's hotshoe, then electrically through a TTL sync cord. The CAMERA tells the flash when to fire and quench, but the meter is not behind the lens, so it's not TTL under our definition in this thread.

Auto strobes like the types discussed here have minimal communication with the camera. They have a light sensor on the strobe which "watches" the camera flash and when it fires, it tells the strobe to fire. The same sensor, or another sensor on the strobe tells the strobe when to quench. But the only signal passing from the camera to the strobe is an "optical" one and all it tells the flash is "Fire!"

Anyhow - this is some food for thought. If anything I've said here isn't correct (I've never used the Tetra5050) please feel free to make corrections.

Cheers

James

Right...so isn't this the same as what Ikelite is doing with the digital TTL strobe controller? Only that the circuitry is on a seperate unit outside the housing?

I agree...this isn't "real TTL". "Real TTL" would only come from a sync cord is electronically connected to the hotshoe. So my point is that neither a Tetra 5050/5060 housing nor a Pt015/020-with Ikelite solution uses "real TTL". So the much cheaper PT housings offer about the same option for strobe control as the much more expensive Tetra.

This is why I started down the DSLR path. I wanted to get a wired connection to my strobes. Unfortunately most of the housing manufactures haven't figured out TTL for DSLRs yet (although some have). I'm counting on Ike's promise to crack the DSLR TTL codes. I hope he will crack iTTL and offer the cuiruitry as an add-on that I can buy later to upgrade my D70 housing. But this is all imaginary until I get my housing and camera. I'm on the wait list for both.

Hmm...

I agree...this isn't "real TTL". "Real TTL" would only come from a sync cord is electronically connected to the hotshoe.

This is where I don't agree. One of the main points of my post is that it doesn't matter HOW the camera and strobe communicate. It can by via sync cord, fiber optic with a converter on each end of the fiber, via radio transmitter, etc.

What matters is that the flash meters are behind the lens, reading the flash light as it comes in. That's the strict definition of TTL.

The Ikelite TTL sensor fits within that definition if the camera that sends the signal to the controller is a TTL camera, using a TTL system to control the camera's internal flash.

I've got a lot more to talk about on this topic about preflash, which kind of TTL system is "better" etc, but I'll hold off until more peoplel have chimed in. This is afterall just my one opinion from my experience - I'm sure there are others.

Cheers

James

Everything that James has said so far is factually correct, and I also agree with his definition of TTL. TTL is a metering system, and is not dependent on a standard camera to strobe communication system (the hotshoe & 5-pin sync cord standard). Personally, the optical communication available on the Nikon SB800 and D70/D2h cameras is very attractive. I don't care if it communicates via ESP, as long as the protocol works.

Olympus builds in much electrical voodoo to its TTL signals. This may or may not be to discourage aftermarket flash accessories. Light & Motion took the easy way out, and just forced the external strobes to mimic the internal flash. This was not a new idea, Ikelite had been doing it for nearly 2 years when Light & Motion released the Preflash ROC system. The differences were that Light & Motion combined both manual and ttl flash control into a very convenient unit, and housed the sensor inside an opaque housing so it could not be influenced by other strobes.

Ikelite and Aquatica are actually decoding these electrical signals, and turning them into a signal that underwater strobes can understand. Aquatica is boldly attempting to make their ICU system compatible with strobes from multiple manufacturers. Ikelite has chosen to make the system work only with the strobes they know and can control.

The drawback to the Tetra's "Electronically controlled flash esposure system" (How's that?) is indeed the problems created by heat from the flash. The lens on the camera will fog if too many shots are fired with the internal strobe on. I use it sparingly. Usually on light subjects, or in one shot and the subject may be gone situations.

It's the ROC control that makes the extra $ worthwhile. Apparently, there's no way to convince anyone until they have used it.

Rand

If the quenching isn't done in real time as the exposure is created, a digital system's "thru the lens" isn't the same as a film camera's "thru the lens". If the camera pre-meters the scene via a pre-flash, it may indeed be metered thru the lens, but to avoid confusing it with real-time TTL it makes sense (to me) to refer to it as D-TTL. I realize others may use different nomenclature - that's OK by me.

Rand - I like the way the camera's strobe can be turned off on the CP5000. The hot-shoe is active, but the on-board strobe doesn't fire.

One problem with "watching the camera strobe TTL" is loosing the full power of a big underwater strobe. When the little camera strobe runs out of steam and stops flashing, the big strobe stops. We do emulate true Olympus TTL through a sync cord to the camera hot shoe, but the signal is converted to allow use of Ikelite digital protocol strobes. See following URL:

http://www.ikelite.com/web_pages/2olympusTTL.html

I think UWPhotoNewbie might be experiencing some confusion here between the old Ikelite system and the new Ikelite system. The new Ikelite 5050 and 5060 housings do not need the control units anymore. Nor does the camera's internal flash fire at all. The new Ike's are hardwired from the camera to the strobe, with some interpretation hardware in between. This is, in my opinion a quantum leap forward. I have long been an advocate of fiber optic sync systems -- and I still am -- as long as strobe output is controlled manually or with an auto sensor that is part of the strobe head. I have not been completely successful with any system that tried to mimic the camera's quench system, though. I have not personally used the Tetra system, which is quite a bit different, in that the sensor is inside the housing, where logically it would seem like it has a better chance of keeping on track.

The new Ikelite system and the Olympus PT-020 (and 23) are as close to film TTL as we have ever seen this class of camera. I don't have any experience with the Nikon or Canon viewfinder digitals, but I can tell you from experience with the Olympus X0X0 cameras, both above and below the water line that the camera does a superb job of controlling flash output -- whatever you want to call it and whether it works from a pre-flash or not. I personally am looking forward to trying the housed FL-20, the Ikelite housing with hard-wired flash control, and Matthias Heinric's hard-wired interpreter for TTL strobes.

I used Ikelite slave controllers with my 3040 and 5050 but never got good results in TTL mode. So I used them to control my DS 125s in manual mode. This worked fine.

Then I got Ikelite manual controllers. IMO they are no real improvement over the manual settings on the DS 125 when using the 5050 in slave mode.

In mid January I started using the new Ikelite TTL. With over 25 days of dive experience I can safely say this TTL approach really works. It pours out light in ships engine rooms yet doesn't burn shiny fish shot in the open.

With over 2 years of shooting manual strobes I feel it's almost unmanly to use TTL. Like driving a car with an automatic transmission. But it works so good I can't go back

I personally am looking forward to trying the housed FL-20, the Ikelite housing with hard-wired flash control, and Matthias Heinric's hard-wired interpreter for TTL strobes.

And when you do, I'll make sure a Tetra 5050 is in your bag, and you'll find that it is every bit as accurate, and offers 12 manual powersettings at the tip of your thumb.

I won't argue that Olympus can meter strobe output with the best of them, there are times when you don't want a "properly" exposed picture. I don't think Olympus TTL would have exposed that frogfish pic you won the Bonaire Digital Shootout Macro competition with as well as you did, preserving shadow and not blowing out the lure.

You can get close to the functionality of the Tetra with Matthias' adapter (but it requires a reach to switch from ttl to manual), and with Ike's ds125 (also a reach, and only 4 power settings). My point is, you can't match it.

I think UWPhotoNewbie might be experiencing some confusion here between the old Ikelite system and the new Ikelite system.

Actually, I'm not confusing the two systems at all. My comparison was:

Tetra 5050 system with "strobe watching" TTL

or

PT015 5050 system with Ikelite "strobe watching" TTL through TTL sensor

In this case you get simulur TTL with the added flexability of being able to upgrade as you go for much less money.

My comment was precisely that for all the money that you can spend on a Tetra you should be able to get the kind of direct hotshoe wired TTL that you get from the Ikelite housings. If you like to go both ways with the Ikelite (manual and TTL) you can do that by adding the manual controller and connecting it to the port (ignoring the sensor). Still this system is 1/2 the price of the Tetra.

Now having said this I'll have to admit that I never really got my Ikelite TTL sensor to work right. On one dive trip it wouldn't do TTL but worked in manual. I sent it back to get it "re-tuned" to sync better to the Canon preflash. On the second trip it flooded on the first dive (first time I had it underwater since sending it back). Still need to send it back. So not enough testing to say anything conclusive and TTL is probably not very good on the primitive/compact Canon S300 anyway. Any different experiences with this setup on the PT015? Sounds like the Tetra system really works.

UWphotoNewbie: We do not recommend the TTL Sensor with the Canon "A" and "S" series cameras. You should let us exchange the flooded unit for a Manual Controller............

UWphotoNewbie:  We do not recommend the TTL Sensor with the Canon "A" and "S" series cameras.  You should let us exchange the flooded unit for a Manual Controller............

Ike

Is the "loosing the full power of a big underwater strobe" problem you mentionned the reason why you do not recommend the TTL sensor with those cameras?

Thanks

WetA70: Right hand column of following URL explains:

http://www.ikelite.com/web_pages/dig_definitions.html

UWphotoNewbie: We do not recommend the TTL Sensor with the Canon "A" and "S" series cameras. You should let us exchange the flooded unit for a Manual Controller............

Update:

Well I returned my TTL controller and received a new manual controller just as Ike promised. Total time was about two weeks. FAST! I can't say enough about Ike's customer service. Thanks Ike.

By the way, my topside tests of the new controller were great. I love having at least one manual control into my P&S camera. I was quickly able to get good exposures with only one or two test shots. I expect that once I get this dialed in I should be able to get good exposures for the entire dive for similur compositions/conditions. When I bought the TTL controller, the manual controller was not available. I'm glad that Ike responded by updating his website and product line with this solution.

I posted a full report of my experiences with Ike's customer service in the lighting section. Needless to say, I have no reservations about purchasing Ikes housing for my D70.

TTL is a term used to describe flash metering.  Originally it stood for "Through the Lens" metering.  As in the light meter that sets the flash power is inside the camera body, behind the lens somewhere.

It has been suggested to me that actually/originally TTL referred to the design of the logic that controlled the flash. TTL is a term in electronics:

http://www.xs4all.nl/~ganswijk/chipdir/ttl.htm

The meaning Through-The-Lens (apparently) was adopted later.

/Anders

The reference you posted is about circuit design. In that context TTL means Transistor Transistor Logic and describes how the different components on the circuit interact.

Cheers

James

Exactly! ...and it was suggested to me that when someone (Nikon?) first presented a TTL camera/flash it was named TTL because it used this circuit design - not because the metering was done behind the lens.

Later... who cares about circuit design. Through-The-Lens describes what it all about!

/Anders