The manuals for both of these don't seem to be clear on this, but can the 5d mk iii fire the 600 RT remotely, by radio, without a 600RT on camera as the master or the optional radio trigger on the hot shoe? IOW, does the mk iii have built-in radio triggering for off camera flash with the 600rt?

What I would Iike to accomplish is to fire 2 600s by radio from the camera, and maybe add a 580EX ii fired optically by the other OCFs.

No, it doesn't have a built in RF transmitter. I also don't think you can mix both wireless ettl modes together, but you could of course set the 580 manually and put it on an optical slave or something (i could be wrong, though).

No it won't you need a 600 ex rt or st e3 rt on camera to fire other flashes. st e3 does have optical option. Why bother with optical when you have these. I use 3 600's and a st e3 and they work great.

I am a bit disappointed in their vague description of the wireless capability. I see it has confounded some review sites as well. Unfortunately, it would seem that it does not have a dedicated RF transmitter, as I too had thought. Apparently the wireless functionality they refer to is the ability to control all 600exRT functions via the camera LCD. Not a huge advertising point IMHO, since the 600's interface is hugely improved over the 580's.

I've used two 600s in conjunction with my 60D, and triggered them both off-camera, optically, via the 60D's pop up flash. In this sense, I am still a step ahead gear-wise, since using the 5D MkIII would necessitate another piece of gear if I wanted to use both flashes off camera! (Trying to convince myself this is a good enough reason not to indulge in a 5D MkIII !)
For radio-trigger, I've mounted one 600 on my 60D, set it to radio, and fired another in a separate room.

Muzt wrote: ...st e3 does have optical option.

No, it doesn't.

Yes I found this a little confusing myself when reading the 5D3 manual.

Zenon Char wrote: Yes I found this a little confusing myself when reading the 5D3 manual.

What page?

Top of page 194. Never really explains you need a transmitter of some type. I read the whole manual over time but I just looked up wireless flash in the index to check it out.

I'm using an e manual I downloaded from Canon so I'm as assuming the page is the same. I never take the manuals out of the plastic.

Zenon Char wrote: Top of page 194. Never really explains you need a transmitter of some type.

It is a little confusing unless you realize that page 194 is devoted to Flash Function Setting, and is a continuation from previous pages. That section starts on page 191 with this:

Yep you are correct. It does pay to read the instructions from the beginning. I had no real desire to buy the 600 but I needed a new flash. Have PCB triggers,etc. Figured if I'm going to spend a big chunk of change on a new 580 I may as well spend more on RT for the future. After exploring Canon RT more I decided I liked the system and am upgrading.

Zenon Char wrote: ...After exploring Canon RT more I decided I liked the system and am upgrading.

Yeah, I'm with you there. Since I don't have any studio strobes and no radio triggers at the moment I am also going to get a couple of 600EX-RTs sometime soon.

Syl states that as well. Count so far - one 600EX-RT in hand, ordered my ST-E3-RT from B&H last night. 2 more 600's to go. Like ET said - Ooouuuch - but it will be well worth it.

http://pixsylated.com/blog/deciding-between-canon-speedlite-600ex-rt-and-580ex-ii/

On another topic it will be great to be able to adjust the flashes from the ST-E3-RT but I was trying to figure out how to fire the flashes with my Sekonic L-358. The dedicated transmitter only works with PW. I normally attach a PCB transmitter to the L-358 and a receiver/s to the flash/flashes which still has me going to each flash to adjust.

Someone suggested to have both the ST-E3-RT and L-358 in hand and use the test button on the Canon transmitter. Only good for manual but that is the only time I use the L-358. In ETTL I chimp and adjust ratios, etc. That will do until until hopefully Sekonic comes out with a Canon friendly transmitter module. In the mean time I will just hang the L-358 around my neck. I figure I will use that method for quite some time

Well I call Sekonic today. They have no intention of producing a Canon RT module. They work exclusively with PW but it is pretty early in the game. Eventually Nikon and others will go RT so PW and others will likely see a decline in business. That will take years. Lot's of happy third party Rt users out there.

Got my transmitter last night. Works really well. Easy to navigate menus. Love the LCD light (like the flash) goes on if you press any button and you can make it stay on. That is worth it's weight in gold alone

Noticed one thing when the transmitter is in master and my 600 is in slave while in ETTL. If you do an FEC adjustment on the transmitter (or via Q button on camera LCD) it shows the change on the transmitter LCD output level bar. It does not show it on the flash. It works as I tested it from -3 to +3. Put the flash on C and tried the FEC for C in the ratios and it did not show either, but it did work correctly.

When in other modes like M or Gr, any change you make from the transmitter/camera does show on the flash LCD.

I was a little concerned at first but appears to be working correctly. I guess Canon decided it was not necessary to show this info in ETTL. In case anyone notices this as well.

From page 27 - FEC adjustments. I guess this is their explanation.