Found this from Bob Adkins
The Canon EOS E-TTL II Flash System
With the announcement of "E-TTL II".
There is a new flash algorithm, similar to the existing E-TTL, but designed to give better results under difficult situations, such as when there is a very bright reflection from a small object in the scene.
Just like E-TTL there is a preflash which is used, along with ambient light metering, to determine the flash exposure using the center 17 metering zones. Zones which differ greatly in brightness are given less weight since they are likely to be reflections from small, highly reflective, objects.
With lenses which return distance information, this may also be taken into account by the flash algorithm, but the point to note here is that the E-TTL II system works with ALL Canon lenses, it's just that those which return distance information provide an additional parameter for flash calculation. Even without distance information ETTL II should provide better results in difficult situations. So all your lenses will work just fine with E-TTL II, it's just that under some circumstances, E-TTL II compatible lenses might give slightly better exposure when using shoe mounted on-camera direct flash.
In general, if a lens uses a ring type USM motor, it returns distance information and so is E-TTL II compatible. Not all USM lenses use ring USM motors. Those which do not offer full time manual focus ( e.g. the Canon EF75-300/4-5.6 USM), do not return distance information. Lenses using AFM (arc form motors) do not return distance information (e.g. 50/1.8, 24/2.8).
Notable lenses which you might think would return distance info but don't are the 50/1.4 USM and the 85/1.2L USM. The tilt-shift (T/S) lenses are manual focus, and so of course do not supply distance information.
Non-current lenses which should return distance info include the non-IS telephoto lenses such as the EF 500/4.5L USM, 300/2.8L USM, 600/4L USM
Note that E-TTL II does not use distance information when a direct, camera mounted, flash is not used, even with E-TTL II compatible lenses. These situations include:
- When bounce flash is used
- With ETTL wireless flash
- With macro flash
The reason for this is presumably that under those circumstance the flash-to-subject distance will be different from the camera-to-subject distance (which is the information that the lens returns), so the camera cannot know the flash-to-subject distance - and that is the information it would need to fine tune the E-TTL II algorithm results. The bottom line seems to be that the new E-TTL II flash algorithm will give better results with all lenses, but if your current lens isn't E-TTL II compatible, it's no big deal. You'll still get better results than you would with the older E-TTL system.
Here is a list of current Canon EF series lenses which fully support E-TTL II by supplying distance information. It was updated on 03/04/2004 based on information supplied by Chuck Westfall of Canon
*Indicates discontinued product
EF20mm f/2.8 USM
EF24mm f/1.4L USM
EF28mm f/1.8 USM
EF35mm f/1.4L USM
MP-E65mm f/2.8 1-5x Macrophoto
EF85mm f/1.8 USM
EF100mm f/2 USM
EF100mm f/2.8 Macro USM
EF100mm f/2.8 Macro*
EF135mm f/2L USM
EF180mm f/3.5L Macro USM
EF200mm f/2.8L II USM
EF200mm f/2.8L USM*
EF300mm f/2.8L IS USM
EF300mm f/4L IS USM
EF300mm f/4L USM*
EF400mm f/2.8L IS USM
EF400mm f/4 DO IS USM
EF400mm f/5.6L USM
EF500mm f/4L IS USM
EF600mm f/4L IS USM
EF1200mm f/5.6L USM
EF17-35mm f/2.8L USM*
EF17-40mm f/4L USM
EF20-35mm f/3.5-4.5 USM
EF24-70mm f/2.8L USM
EF24-85mm f/3.5-4.5 USM
EF28-70mm f/2.8L USM*
EF28-80mm f/3.5-5.6 USM*
EF28-105mm f/3.5-4.5 II USM
EF28-105mm f/3.5-4.5 USM*
EF28-105mm f/4-5.6 USM
EF28-105mm f/4-5.6
EF28-200mm f/3.5-5.6 USM
EF28-200mm f/3.5-5.6*
EF28-300mm f/3.5-5.6L IS USM
EF35-135mm f/4-5.6 USM*
EF70-200mm f/2.8L IS USM
EF70-200mm f/2.8L USM
EF70-200mm f/4L USM
EF70-210mm f/3.5-4.5 USM*
EF70-300mm f/4.5-5.6 DO IS USM
EF90-300mm f/4.5-5.6 USM
EF90-300mm f/4.5-5.6
EF100-300mm f/4.5-5.6 USM
EF100-400mm f/4.5-5.6L IS USM
EF-S18-55mm f/3.5-5.6 USM
EF-S18-55mm f/3.5-5.6
If your Canon EF lens doesn't show up on this list, it does not feed distance data back to the camera through the electronic mount.
As a reminder, distance data is never the only factor that controls flash exposure in E-TTL II. It is an optional data point, no more and no less. E-TTL II remains functional with *all* Canon EF lenses, but when using direct flash, E-TTL II is at its best when distance data is available.
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