ahhhh I see. Makes sense in regards to when you say "how long the flash fires" and you're saying that the TTL is able to read the distance, so the TTL capability on the flash knows how far the subject is from the flash therefore applying the particular length of time the flash fires?
This is very interesting, and this makes the most sense to me in our exchange. I need to go out shoot in different light situations in the TTL mode, and wait for development. For me I need to know as much as I can before shooting with a new "tool"
I've been reading other forums which I cannot link here because the moderators think that is spam or something, where they are having a similar conversation...let me quote from it:
began quote from the i-camera-forum
The 1/50 sync speed means that low-power flashguns like the SF24d are almost useless in bright light.
The main use for a portable flashgun in daylight is as "fill-flash" to lighten deep shadows in a sunlit subject.
You set the shutter speed to (for the M6) 1/50, then set the aperture to get the correct daylight exposure or maybe half a stop underexposed.
(With ISO400 film, in sunlight would mean 1/50 at about f/64, so already you're stuck. Switch to ISO50 film so the exposure is something a Leica can do - say 1/50 at f/16.)To get a good "fill" effect, lightening the shadows but not too much, you need the flashgun to deliver two to three stops less light than you'd need if the flash was the only source of light. So (if the flash is in Auto mode) you tell it that the aperture is f/8 not f/16.
Unfortunately, the maximum working distance of the SF24D at ISO50 is about 2m, which severely limits its usefulness. For longer distances you need much a more powerful flashgun.
(The problem is that that the flashgun's 1/1000 second flash has to balance what the sun delivers in 1/50 sec. If the camera has a faster sync speed, like the 1/180 of the digital Ms or 1/500 of a traditional Hasselblad, fill-in flash is much simpler.)As an alternative to switching to slow film, you can use a neutral density filter on the lens. This solves the problem of getting a usable aperture at 1/50 sec in bright light, but does not alter the other problem of getting a little flashgun to balance the power of the sun.
PS: if you don't have the manual for your SF 24d, an internet search will find a scanned copy.
end quote from the i-camera-forum
The SF-24D I hear on an m6 is exactly the same as the SF20D only that it was meant primarily for the m7. The SF24D I hear works exactly like the SF20 on a M6.