Bullshark, You have raised a lot that deserves an answer, but to keep it clear, will only address one issue at a time (ok, two in this one).
RC means Radio Controlled. Several camera makers use that to control flashes. Oly makes the flash control for Panasonic, but Panasonic's don't have a RC system. Oly is not the only camera maker to have such a system, but will spare you a review of each maker.
Manual versus Auto control of the flash. THERE IS NO MANUAL CONTROL OF THE FLASH IN AN LX-5. Using the EV control system to adjust the automatic system is not manual. If you had "manual", it would be one of the choices and you then have options of much flash you wanted (like 1/64th or 1/4).
The Oly zx-1, while very similar to the LX-5, does have manual control.
As, even in manual, with the LX-5, you are shooting with the camera in auto flash mode, it is very easy to find condtions where the system will incorrectly expose the image. But it does work most of the time. Shoot 10,000 images a year and you will find conditions that it will not work correctly.
Your comment about "auto" system not working underwater is almost true, as regardless of what setting you put the camera in, if you use the flash, it is just another "auto" program. Because it works most of the time, one just needs to know what to do when it does not.
There is a lot to like about the LX-5 as an underwater camera, but the flash control is not one of them. I love the lens and the special sensor, and it makes a great travel camera.
Next up: Why using the camera adjustments will not work and how to easily demonstrate the issue on land
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So you take a pictures and it is over exposed in TTL...how do you fix it?
The problem here is why it is over exposed and how TTL actually works.
TTL works by adjusting how long the actual flash is. It does not adjust the strength of the strobe (at least with the LX-5 anyway).
Here is a very simple test to show the issue (on land)
Put the camera in manual and forced flash on and:
1. Set your camera to F5 (best resolution.
2. Set your iso to 80 (lowest number and best image quality)
3. Set your shutter to 1/1000 (very fast for freezing motion)
Now take the following images when it is very sunny outside:
With the camera outside the case, shoot one set of images with the flash up and one with the flash down:
1. An image about 5 ft away, inside, with fairly dark conditions.
2. An image outside, in light shade.
3. An image in bright sun.
All the images should be almost black (except the bright sun, which should be just dark) without the flash and ok with the flash.
Now put the camera in the case and turn on two strobes and re-shoot the same images.
Note: I used YS-1's for my test, but YS110's, and most other strobes will have the same issue.
I get a great indoor shot, way over exposed in the light shade and bright sun.
So why didn't optical TTL work correctly, and why not just attempt to adjust the camera's output?
Well, adjusting the camera only works if the results are consistent...which they obviously are not. If a cloud goes over, you would suddenly have over way under exposed images.
The reason it does not work is tied to how this system works, as is the correction.
Before explaining, try this....with the same camera setting, turn the strobes on manual (the first setting for a preflash) and adjust the indoor image until you get a good exposure and then go shoot outside...you should see a huge difference.
So, here is why it did not work:
1. The YS-1 are very strong strobes compared to the tiny built in strobe.
2. Each strobe only has a range of time it can control, and the camera is set to expect the strobe strength of it's own strobe.
3. Once you get to the fastest time, the strobes cannot go any lower.
There is a small amount of adjustment on the YS-1, but not enought to correct for wide changes, particularly when less strobe light is needed.
Why does manual control appear to be much better? Well, you are adding a fixed amount of light, so distance is more important than ambient light. Yup, it means you need to adjust the strobes if you change distance, but that is easy to judge.
Is this a good answer? No..because YS-1, in manual, it does do not send out a preflash, so the camera strobe will fire at maximum in darker conditions and only turn itself down if very light conditions. Full flash means more heat and fewer pictures per battery.
So my recommendation is to use TTL in darker conditions and manual in light conditions and not attempt to constantly adjust camera settings.
Note: Anyone that takes a photography class from me gets to see this effect for themselves and how to correct for it.
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So which to adjust, the camera or the strobes? This assumes you are ajusting for a fixed difference between the strobes and the camera.. which is not the case in very light conditions. But lets assume, even in the dark, you need to calibrate the system to get a good exposure.
Well, if it is too dark, your only choice is to adjust at the camera, as the strobes don't have any "lighter" adjustment.
That actually is unlikely, but if it happened, then you have to adjust the camera.
If too dark, you get the choice of camera or strobes. If you adjust the strobes, it is a one time adjustment and you shoot pictures.
If you adjust the camera, and want to shoot flash pictures on land (like that great dinner party after the dive), then you have to adjust the camera back to center and then remember to adjust back when taking pictures.
Of course, if you only use the camera underwater, it does not matter, but I don't know many people that travel with several camera's (well except for me).
For that reason, I know of no professional (although there most likely is one out there) that would suggest adjusting the camera, unless you have to (because the image was too dark.
Regarding the "pots" not being consistent on strobes...well one would hope they are, or you would never get consistent images. I can only assume you are not a photographer, or you would know that. I had to turn down mine and have used the same settings for over 2 years.
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I don't recommend anyone use spot focus for underwater images. Obviously one can use anything they want, but there are lots of times one will get bad exposures doing so, if you are using some of the more advanced imaging methods. If all you shoot is snap shoots, use anyone you like.
There are times where not having shutter lag is the only way to get the image (young angle fish, for example). To do that, you need to prefocus the camera and then wait for the fish to get into the correct location. That requires you find something the correct distance, focus (which also sets the exposure) and shoot when the fish is at that distance. Use spot and where you pointed the camera will be exposed correctly....but not necessarily the fish. While there is no perfect solution to this, you will get more good images if you set the camera to multi-metering.
Test: Hang and object on a line from a reasonably tall ceiling, and have someone swing the object towards you. You objection is to take an in-focus picture, just as it reaches it's closest. Bonus points for filling the image in the frame.
Note: make sure the arc is at least 5 or 6 ft, so it is moving fairly fast.
Try just shooting the image..I've seen a lot of people try for hours and not get one good image.
Then pick the distance it will get, prefocus the camera to that distance and try it. Everyone I know can do it.
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If I provide much more, I might as well just send everyone my class.
In the old days of film, a professional was someone, for the most part, that understood the technology and the craft. The camera controls were rather trivial, as all one had was the speed rating of the film, shutters and f-stops. View camera's with swings and tilts were the complex stuff.
Today, we have layer upon layer of complex technology, none of which is explained (trade secrets?), and even less is is taught. Each camera maker,can use totally different method to get the same results, and until one actually has a problem, it is just some sort of black box effect.
I see people with Fuji's, Canon's, Nikon's, Oly's and Panasonic's in underwater housing (too name a few), and the problem is that what works best for one system may not be the best for another, even though they call things roughly the same.
Today, if you have a problem, there are no generic solutions for the most part, as it depends on how that camera actually does things.
As an example, the panasonic GH series addresses the over exposure problem by sending out a lower power, second preflash, so now the strobes will not sync with the camera, so you don't get any over exposed images, you get ones without any strobe at all.
