Is there an advantage in optical transmission with TTL that you lose with radio?

[RezaM]

I have an ST-E3-RT and 4 600EX-RTs and that is all I use for lighting. I use both E-TTL and Manual. I always prefer to use my radio for E-TTL but was wondering, is there an advantage whatsoever for someone in my case to ever use optical when all I need is Radio transmission either in E-TTL or manual? Is there an advantage in optical transmission with E-TTL that you lose with radio? I read somewhere that may be the case where the optical communication between speedlights for determining exposure in TTL is more accurate with optical transmission than radio. It may be that the Nikon folks are pushing that thought but wanted to check. Thank you all.

[RobertTheFat]

One advantage of radio is that the receivers on the slave units are omnidirectional or nearly so, which means that the slaves ordinarily have no positioning requirements relative to the master. If there are multiple photographers present, there may be a risk that two or more of them are using the same RF channel, but presumably that can be worked out ahead of time. And I suppose there's also a risk that multiple photographers may set off each other's optical slaves. See if Skirball, who knows a lot more about such things than I do, weighs in. But my impression is that the majority opinion these days is that radio is better.

[RezaM]

Hi Bob and Skirball

Thanks for your response. I understand the implications of radio and optical. My actual question was is there an advantage in terms of the pre-flash associated with E-TTL on the optical that would be lacking on the radio transmission that would render more accurate readings by the system in optical. It seems some claim that the pre-flash in optical more accurately judges a scene and therefore the command to the slave speedlights is more accurate. To put it simply, E-TTL would be more accurate with optical than radio.

Thanks for your help.

[TCampbell]

You may be confusing two concepts.

There's the E-TTL "metering" concept where camera meters (with no flash), fires a pre-flash (at low power) while metering again, compares the difference between the two, then sets the final power level for the shot when the camera finally opens the shutter to capture the image.  That E-TTL pre-flash / flash happens regardless of radio or optical.

The camera compares the no-flash metering to the pre-flash metering across multiple metering zones in order to detect things that previously used to fool A-TTL or older systems.  By doing this, it's able to detect highly reflective surfaces (which return more light than typical surfaces and would fool a flash into thinking it was using too much power) or also detect light sources within a scene ... where the difference between no-flash and pre-flash is minimal and might fool the camera into thinking it needs more power.

This happens even if you just have a single on-camera flash and has nothing to do with how the camera handles communication to remote units.

Then there's the notion of communication between the flash units.   Optical doesn't have any technical advantage here.  Radio is more reliable and flexible (although I do recall an issue where the 580EX II speedlight used to create RF "noise" when it fired and this would interfere with some radio triggers.)  The 600EX units don't have this issue.

Even before Canon offered flash units with radio capabiliy, photographers favored radio trigger systems because of the flexibility it offered.

[RezaM]

Thank you very much TCampbell. That's great information. So there's really no reason to use optical if I use 600s with an ST-E3-RT?

[TCampbell]

The optical offers you compatibility with flashes that cannot do radio.  E.g. if you had 580EX II's or 430EX II's.  You can't mix both radio and optical at the same time -- so if there's one flash that can only support optical, then all the flashes would need to be set to use optical (note that the ST-E3-RT transmitter can only do radio -- it doesn't offer an optical mode.)

[Skirball]

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@RezaM wrote:
Thank you very much TCampbell. That's great information. So there's really no reason to use optical if I use 600s with an ST-E3-RT?

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To answer the question you've been getting at all along - No, optical offers no advantage that can't be achieved with the proper RF system.   Conversely, there are several advantages to RF that optical lack.  It would be a handicap to use the optical system if you have 600s and a ST-E3-RT.

If you don't have that system yet, but are considering it, keep in mind there are alternate options that are cheaper and can even have features the Canon system doesn't - such as wireless second curtain sync.

[RezaM]

Thank you so much for the great information. I do have the 600s and an ST-E3-RT and that's primarly what I use. I don't have much need for the wireless second curtain typically as my subjects are not moving very much. Besides the reliabilty and ease of the canon radio system I chose the ST-E3-RT for the radio shutter release feature which has come handy. I suppose the other option providing wireless second curtain you're suggesting may not provide that. Is there a wireless system that provides both features and is similar to the Canon radio in terms of capability. Thanks again.  

[TCampbell]

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@Skirball wrote:

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@RezaM wrote:
Thank you very much TCampbell. That's great information. So there's really no reason to use optical if I use 600s with an ST-E3-RT?

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To answer the question you've been getting at all along - No, optical offers no advantage that can't be achieved with the proper RF system.   Conversely, there are several advantages to RF that optical lack.  It would be a handicap to use the optical system if you have 600s and a ST-E3-RT.

If you don't have that system yet, but are considering it, keep in mind there are alternate options that are cheaper and can even have features the Canon system doesn't - such as wireless second curtain sync.

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There are cheaper systems ... certainly.  But those tend to be extremely basic manual triggers (via radio).  There are a few 3rd party systemw chich offer ETTL, but those support the more basic capabilities of ETTL and they tend to be QUITE expensive ... and still have reliability problems.  

PocketWizard's mini/flex combo is probably the most well-known.  I wanted it, but it wasn't cheap.  But the more I dug into it, the more I found that a lot of people preferred simpler systems because the PW's higher-end units weren't all that reliable (it's not that the units would "break"... it's that the percentage of times in which the remote flash didn't fire was higher than what you might expect from such a system.)  I decided to wait it out a while and see what happened.

What happened is Canon introduced their own radio system.  I have a couple of 600EX-RTs with the ST-E3-RT and I can say that it's ROCK SOLID reliability.  It _always_ fires.  The off-camera units can be completely controlled via the camera menus.  Other than hitting the power switch, there's pretty much no reason to actually walk over to your flash.  This means faster shooting because you can adjust as needed without visiting the flash.  If the flash is located in a hard-to-get-to spot (inside a soft-box, for example), I don't have to worry about it.

I don't know of any system that offers as much feature-rich functionality in their wireless radio flash system as Canon.

But there is that little issue of 2nd curtain flash.  WHY they don't have 2nd curtain flash when using the flash remotely boggles the mind.  Especially when you look at some other features that they DO support via radio triggering ... like multi-strobic flash mode and high-speed-sync mode.  Certainly if you can do those... you can do 2nd curtain mode.

I'd read from some (probably not credible) post that it was a patent issue.  But from what I've learned about patents, you can't take two stand-alone patents, slap them together, and claim that you have a 3rd patent and expect it to be enforceable.  2nd curtain isn't "new" and radio isn't "new".  ergo, slapping "2nd curtain" and "radio" together does not make a 3rd patent... it's just a logical use of the previous two ideas.  It's not non-obvious (one of the criteria for patents).  Every photographer who wants to take their flash off-camera says "oh... and I want to keep all those features I had when it was on-camera."   So while I've heard the patent issue a few times... I doubt that's the reason.

[RobertTheFat]

TCampbell wrote:

I don't know of any system that offers as much feature-rich functionality in their wireless radio flash system as Canon.

But there is that little issue of 2nd curtain flash.  WHY they don't have 2nd curtain flash when using the flash remotely boggles the mind.  Especially when you look at some other features that they DO support via radio triggering ... like multi-strobic flash mode and high-speed-sync mode.  Certainly if you can do those... you can do 2nd curtain mode.

I'd read from some (probably not credible) post that it was a patent issue.  But from what I've learned about patents, you can't take two stand-alone patents, slap them together, and claim that you have a 3rd patent and expect it to be enforceable.  2nd curtain isn't "new" and radio isn't "new".  ergo, slapping "2nd curtain" and "radio" together does not make a 3rd patent... it's just a logical use of the previous two ideas.  It's not non-obvious (one of the criteria for patents).  Every photographer who wants to take their flash off-camera says "oh... and I want to keep all those features I had when it was on-camera."   So while I've heard the patent issue a few times... I doubt that's the reason.

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It depends a lot on where and when a patent application is filed. In recent years the U.S. Patents & Trademarks Office, backed by the tacit compliance of a capitalist-leaning Supreme Court, has been annoyingly favorable to dubious patent claims. From time to time there has been talk of trying to restore balance by Congressional action. But the capitalists have been gaining strength in Congress in recent elections, so any such action is unlikely in the foreseeable future.

In other countries, obviously, YMMV.