Av and Tv are the exposure and aperture settings that are set in DSLR Focus for the Focusing Run. Once the focusing run is finished Tv is set to Bulb and the Av (f/stop) is set at the original focusing setting (2.5?) or slower (2.5+) (but not faster 2.5-)
You have to be in M to be able to set these in the first place.
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