cgardner
Offline
Dedicated FM
Upload & Sell: Off
|
 p.1 #13 · E-TTL strobe on emergency scenes | |
Carmen Miranda wrote:
Unfortunately Canon refuses to acknowledge that their E-TTL system has any limitations whatsoever.
That's not true.. Wouldn't you consider completely changing it admission the previous system didn't work well?
Canon film cameras metered off the film during the actual exposure in a direct feedback loop. Canon called it "TTL". The move to digital sensors prevented that so the metering shifted to the viewfinder, with flash metered before the shutter opened via pre-flash.
The first iteration of digital metering was called "E-TTL" by Canon. It based flash metering around active AF points and had an "auto fill reduction" algorithm based on EV level which could be turned off via CF.n.
Canon completely changed the metering system again around 2004 with the 20D and later bodies moving from E-TTL to E-TTL II which compares ambient and pre-flash over 35 zones (more on pro bodies) and also uses focus distance information from most USM lenses (but only when flash is used directly).
One of the reasons I didn't jump into the DSLR game until the 20D arrived is negative feedback about how much the AF point based E-TTL sucked. The introduction of E-TTL II in the 20D appeared to solve most of those problems. But it wasn't until I wrapped my brain around how evaluative metering works that I figured out how to get good results with Canon E-TTL II: don't try to out think it. Point, shoot, evaluate, adjust.
Evaluative compares zones and finds the brightest ones, then decides whether they are specular reflections or areas of important detail. By comparing ambient light zone-to-zone which isn't affected by camera / subject distance with flash returns, which are affected by distance, the camera and create a rough 35 zone radar-like map of what is in the viewfinder.
So if using evaluative you can look in the viewfinder, spot the area of greatest flash reflection and know evaluative will err on the side of not blowing the highlights there. If that brightest area of reflectivity isn't closest to the camera and your intended center of interest your COI will wind up underexposed. But what you need to realize that correctly expose that middle-ground with any flash, manual or auto, you will only be able to to that by over-exposing the foreground which is equally undesirable.
So if anything using E-TTL II evaluative metering teaches you to compose flash shots more effectively, putting what is more important in the foreground ensuring better odds of correct exposure. But since it can't precisely meter the scene - there are only 35 large zones - some FEC adjustment will nearly always be necessary to make the exposure perfect.
The technical Albatross of DSLRs is the "R" the reflex mirror. Lose the mirror and use an Electronic Viewfinder instead and the sensor will dump and read the contents of the sensor 30-40 times per second or more. While its processing the data for the EVF it can also evaluate, down to the pixel level of detail, what areas are clipping. That's why some P&S cameras seem to do a better job of exposure control than a DSLR.
Live view? That's just Canon's way to start weaning still camera users away from optical. After all the video side of the house has lived with EVF since its inception. I have an EVF on my Minolta D7Hi and given the choice between an APS-C Canon with EVF and better metering vs what is offered now I'd take the EVF version in a heartbeat.
Chuck
|
