sTTL vs eTTL vs Nikonos TTL.

OK, I'm a bit confused about the differences between these, so I'm going to summarize what I currently think and then perhaps people will be kind enough to correct any errors or elaborate.

Nikonos TTL: The "old" Nikonos method of communicating with a strobe for TTL, similar to film-based "analog" TTL to land based strobes.

eTTL: I believe this is Ikelite's digital TTL- I'm not 100% sure what makes it digital- is this what allows you to use it with a controller to take it up or down stops? Is it metering, talking to the controler which is then talking TTL to the camera, processing the cameras response, adjusting it and then sending it to the flash? I'm a bit confused.

sTTL: I've seen this mentioned from Inon- this is using an optical sync-cord to the preflash from the camera's onboard flash to trigger a preflash from the strobe. The camera meters, and fires its flash, the strobe reads the power level of the flash (as compared to the preflash from the camera) and fires accordingly.

DS-TTL: Sea and Sea equivalent of sTTL.

HeinrichsWeikamp: An adapter that supports nikonos and other standards and does the equivalent of sTTL.

The brass tacks of this is that I have a Canon G9. I plan on ordering the ikelite housing and ULCS arms.

I'm trying to decide on a strobe, and I want to understand just what I'm giving up if I use an Inon strobe rather than an Ikelite one- is actual cable-connected TTL metering that much more accurate than reading the flash on the camera?

Has anyone tried this with a G7? What were the results?

Well, afaik:

For analog TTL, the nikonos protocol seems the most standard, although for housed cameras there might be a converter needed in the housing.

analog TTL works by measuring reflected light from the film plane, that doesnt work with digital sensors, so the camera companies had to think up a different way.

e-ttl and e-ttl II are canon digital TTL protocols

s-ttl is sigma

i-ttl is nikon

Housings translate these camera protocols so that strobes can understand them. The current strobes are digital TTL ready. the HeinrichWeikamp adapter translated it such, that analog TTL strobes understand these as well.

I'm not sure what you mean by reading flash from the camera. If you're refering to reading the histogram after the shot and manually adjusting the flash? There are several manual - TTL threads around. If you are referring to the strobe reading the camera flash (as a slave), it's a mixed answer.

For slave function, the strobe has to see the light. That makes it difficult for weird positions or murky water. Hardwiring has its disadvantages too. No synch cord is idiot proof, they are prone to bending and breaking. So you have to be carefull....

(all this from 8 months digital underwater experience :-)

Celeus and Cerianthus,

A somewhat simplification as I understand it.....

Canon's eTTL and Nikon's iTTL are camera to strobe HARD WIRE connections through a hot shoe. The camera and strobe communicate pre-flash signals, flash output required based on ISO, flash to subject distance and f-stop chosen. Signaling when to "quench" anything less than a full power dump for a "correct" exposure. Obviously, any sytem has limits on light and dark subjects, personal taste, etc.

The sTTL systems and any optical converter "reads" a camera's BUILT IN flash putting out pre-flashes and final flash output and duplicate these through an optical cord connection. I believe on the INON Z240 you have to match a f-stop setting on the strobe to your camera's chosen f-stop (???)

The Heinrich's TTL converter I think is a hard wired version usable on various housings with Nik V and other connectors.

Ikelite puts their TTL circuitry in their housings, matched to a specific brand's camera protocol, and their DS (Digital Substrobe) units read the output digital connection.

Varying reports on accuracy of all type of TTL flash controls, including external optically triggered sTTL or hard wired TTTL adapters abound all over Wetpixel. Many have great success freeing their photography to concentrate on composition and those quick grab shots. Many never practice enough to make TTL work for them and continue to use manual.

You will have to read the numerous posts and decide if you want to try one for your system and put in a bit of time to learn how to use it successfully.

Hope this somewhat helps

dhaas