Originally posted by oliver939 well, I dont own canon or nikon either but on every DSLR you can set your ISO manually on a fixed value or within a certain range (ex: 100-3200). This second case is what I meant by Auto (the iso will be choosen by the camera within this range)
Then, you have the M mode from which you can select the shutterspeed and diaph you want.
My question is what does the TAv mode does more or different than this.
From the five minutes I spent reading, that's not how it works for Canon or Nikon. AFAICT, at least on the APS-c models, AutoISO only works in Av mode, not M mode. Again, that's from google and glancing through the forums (as it's not really important to me whether or not Canon has TAv or not), but I saw several posts that said that.
It's hard to answer your question if it makes assumptions that aren't true. If, in fact, Canon and Nikon allow you to set shutter and aperture via M and the camera adjusts ISO, then they're just different names for the same function like Tv and Av. OTOH, if, as I *think* is the case from other discussions in the past, Canon and Nikon only allow AutoISO with Av, (many forum posts were cautioning that the CaNikons will often allow too slow a shutter speed for the lens before increasing the ISO, also), then TAv is a different mode.