I didn't find anything on Neil's site, but the results with google says Av and Tv both expose for the ambient/background and the flash is for fill. But, I only spent a minute or two on it. I pretty much never use Tv, so not sure how it works in real life.
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PhotosByRDD wrote:
I've seen two statements made that directly contradict what I was taught about Canon eTTL systems. As I've always be given to believe in AV (aperature priority/aperature value) the system assumes ambient as main and uses the flash to add fill. In TV (shutter priority/time value) assumes the flash to be the main light. If you think about it there's a logic to it. If ambient is too bright you tend to close down the aperature. If too dark, to open the aperature to let in more light. So it's not too much of a stretch to assume the user is basing exposure on ambient in AV mode. Shutter speed is often adjusted with the freezing of motion in mind. Nothing freezes motion in an image better than flash.
Take a shot using eTTL flash in AV mode... note shutter speed. Switch to TV mode match shutter and aperature speed and take a second shot. Compare the results and the output of the flash in the two shots. Everytime I've tried it I get a much higher power dump in TV mode than in AV mode. If Canon's eTTL system treated both the same the power dumps would be equal.
As memory serves you can find an article on how Canon eTTL responds to AV vs TV modes by camera flash guru Neil Van Niekerk's www.planetneil.com.
What mode do I use for receptions? It depends on what I'm shooting and the result I'm after. At any given wedding I'm likely to use a combination of AV, TV and Manual modes.... non-flash, bounced on-camera flash, off-camera flash, and mixed on-camear/off-camera flash. ...Show more →
"As we mentioned before, both the Av and Tv (shutter-priority) modes will always attempt to properly expose the ambient light in the background when you use flash - whether you're in bright or dim lighting."
Wes Allen wrote:
Found a little chunk of text on canon's website:
"As we mentioned before, both the Av and Tv (shutter-priority) modes will always attempt to properly expose the ambient light in the background when you use flash - whether you're in bright or dim lighting."
That's pretty much in line with my own experience. I use AV outdoors all the time with on camera light for fill. I usually dial in -2 or -3 stops of FEC...if you don't, the camera will try to expose the subject to match the ambient and they get blasted with light. It will look pretty obvious you're using a flash, but at two or three stops under it looks pretty natural. As others have said though, if I'm using flash as the primary light I always shoot manual. Unless it's really well lit where you're shooting, any mode other than manual will drag your shutter to the point you'll probably get unwanted blur.
I've been getting pleasing results indoors using AV mode with flash
I used to use Manual, but didn't like it as I like to bring in a lot of ambient and couldn't change settings fast enough - but that was events settings where everything happened quite fast. I use AV now
I usually set AV to -1 or -2 EC though
Sometimes I switch to manual if the light is too variable (counter intuitive, but it's to prevent issues where the ambient overpowers the flash causing blur streaks)
Wes Allen wrote:
Not well. In Av or Tv modes ETTL will try to act as fill, rather then main lighting, in M mode ETTL will act as main, and you can adjust shutter to pull in the ambient light. The only time I will use flash outside of M is in Av mode for fill in bright light. Receptions are usually ISO 800-1600, f2.8 and 1/40th or so, to 1/100 if I am shooting with a longer lens.
Tv probably seems like eTTL is acting as main light because the speed of the lens is much more limiting than shutter speed would be in Av. In Av you might end up at 1/4 second and the flash will act as fill just like you would expect it to. In TV, if you limit the shutter to, say, 1/50 and you only have a 2.8 or whatever lens, the flash will try to make a correct exposure. I didn't research... this is just my guess.
As for the original question, I use M 97.3547% of the time. I use Av occasionally when outdoors and things are changing fast, but I really try not to, because my results tend to vary more than I like.... and I'm not a fan of using the exposure lock button. Av tends to not be good with the white and/or black extremes that we shoot at weddings, IMO.
