Quote Originally Posted by roberttalbot View Post
I just wrote a quick reply but it is not showing up, so I will write it again. Oh boy, I should have copied it. I will write it all over again, arghh.

First, thanks Chris Crawford for the interaction and answering the questions.

So I believe you are saying that one need not care about the focusing because when using the flash unit it is about the distance the flash is from the subject. So in other words, here when using the flash focusing is irrelevant but distance and position with the flash is how it works. Am I right so far?

Now I would think that the higher number the aperture (i.e., f16, 22) would give the photograph a depth of field.

I still cannot grabble around the idea that flash users are shooting at 1/50s of a second hand held, would that not cause blur in the photograph or does the flash compensate for that?

Also, here's a hypothetical situation: I have the Leica M6TTL with the flash mounted in TTL mode, and I am in a low light situation. The ISO is set at 1600, my subject is 3.4 feet (1 meter) away from me. I have the aperture set at 16 which the flash on the back gives me the distance of 23 feet. Now that is a lot of feet that it covers, but my subject is only 3.4 feet. Would the TTL know that my subject is 3.4 feet away and give me the correct exposure or does my subject have to be 23 feet away when I shoot the camera?

Does the SF20 Flash unit in TTL mode dictate my aperture, or do I choose the aperature and the SF20 adapts to that giving me the correct exposure.

I hope that I am asking the right questions, and I am not in some other world.

Also, what is the order. You see the subject, the subject is 4 feet away, in the TTL mode what would one do next. I am a bit confused.

I'm thinking that since the TTL acts as a automatic flash, I would just shoot the camera 4 feet away from the subject without focusing (because that is superfluous) at f16 with the ISO at 1600 (can't change that) because I am in a low light situation.

I hope this is right if not, I need correction.
I'll see if I can help.

First, although I've never used an M6 and SF20 combination, I have used other flashes in TTL mode. If my answers are incorrect because of some peculiarity in the M6 and SF20 combination, I'm sure I will be corrected.

Automatic flashes work by measuring how much light from the flash bounces back from the subject. When the right amount of light has bounced back, the flash is turned off. The full process happens in a tiny fraction of a second - usually much faster than any camera shutter.

TTL flashes use a sensor in the camera to measure that bounced light after it comes through the camera's lens. Non TTL automatic flashes use a sensor on or attached to the flash.

In the days of manual flashes, we would measure the distance from the flash to the subject, and that, with the power rating of the flash, would determine what f/stop to set. The closer the flash to subject distance, the smaller the aperture.

The shutter speed has no effect on the intensity of the flash - you just need to make sure it is a speed that works with flash. Unless you have high ambient light, the shutter speed plays no role in exposure.

For an automatic flash, the aperture set on the lens does two things:

1) it affects your depth of field, just like in non-flash work; and
2) it affects the maximum range of the flash.

The table or indicator on the back of the flash will, in combination with the film speed, tell you within what range the automatic function will work when the indicated aperture is set.

Most TTL flashes will let you choose a range of apertures - you just need to remain aware of the range of distances that will give you.