sanity check - 380EX

[single_track]

I have a 5d and 40d. I am venturing over into the strobist world. I will be buying a couple of manual flashes but until I do, I have a question.

My 380ex flash is auto only. I understand this and realize that a manual flash is much more adaptable. I know that manual flashed can go down to 1/8 power, 1/16 power or lower. However, if I use my 380ex with camera in the manual mode, and use auto flash exposure compensation I should get 1/2 power (-1 stop FEC) and 1/4 power (-2 stops FEC). This way I can control ambient exposure with the camera's manual settings and subject’s exposure from 1:1 to 1:4. Correct?

Seems pretty simple but I am asking the flash wizards to correct me if I am missing something important.

Assuming I understand these basics, any other tips in balancing ambient and subject exposure. Does metering mode make a huge difference? (I am currently using e-TTL II in average metering mode.)

Sorry for the dumb questions. Just getting started and have lots to read. Up until now I just set the camera, bang a flash and see what it looks like, then adjust accordingly.

[Titus213]

Sounds reasonable to me. Just note that FEC is from the power level the system determines is optimal for proper exposure and not just a factor of power levels.

Your described method is my normal flash shooting mode. Manual camera, set ambient based on the meter to what I would like, fire.

[msowsun]

However, if I use my 380ex with camera in the manual mode, and use auto flash exposure compensation I should get 1/2 power (-1 stop FEC) and 1/4 power (-2 stops FEC). This way I can control ambient exposure with the camera's manual settings and subject’s exposure from 1:1 to 1:4. Correct?



What is it that you want the 380EX to do for you?

Are you suggesting you want to use the 380EX off camera and use the FEC to control the power? If so, this will not work.

As soon as you take the flash off the camera, it will put out 100% power every time, no matter what the FEC is set to. This is because the flash needs the sensor in the camera to tell it when proper ETTL exposure has been achieved.


Even if you use the flash on camera in ETTL mode, you can not use FEC to set 1/4 power. FEC will not set the power for you. It can only adjust it slightly.

The total flash power output has really nothing to do with FEC. In some cases the flash will put out 100% power trying to light up a scene if the scene is dark, or you use a small aperture (f/22), or if the subject is far away, or you are using ISO 100. Adjusting the FEC up or down won't make much difference if the flash is already maxed out. It still might be dark with +2 FEC.

Conversely, if you use ISO 1600, f/1.8, shooting something 3 feet away, the flash power will already be down to something like 1/128. You just can't see it because it is automatic ETTL.

In this case, adjusting the FEC up or down will have some effect on the power output of the flash, but I don't see how you can predict that it will be 1/4 power or 1/2 power.