rosarioc62 wrote:
im having trouble with the following settings
AV mode, ISO - Auto, F/2.8 flash ETTL. i have set min. cap on SS as 125. shooting indoors. still SS dips below 125. in order to get correct exposure i need the camera to use ISO instead of dipping SS. how to do this please someone help me here. thanks
Get out of Av auto exposure mode.
Set the camera to Manual exposure mode. If you want to leave Auto ISO on, okay... but I wouldn't. Here's why:
Av is an auto exposure mode.
Auto ISO (with M, without ETTL flash) is an auto exposure mode.
ETTL flash (with M, without Auto ISO) is an auto exposure mode.
So you've set up an "auto-auto-auto" exposure mode. Is it any surprise that weird stuff is happening? The camera is trying to use three different AE modes at the same time!
Further, ETTL flash with
any auto exposure mode automatically is set as "FILL flash", firing at reduced power. Usually the flash output is reduced by about 1-2/3 stops. You can override the reduction by dialing up Flash Exposure Compensation (FEC). But that's sort of hit-and-miss.
ETTL flash only fires as "FULL flash" when the camera is set to Manual mode (
without Auto ISO!). ETTL flash and Manual camera mode is still an auto exposure mode though, because the camera's metering system is measuring the flash (it uses a 1/64 power "pre-flash") and controls how much light the flash will put out. You also can increase or decrease FULL flash using FEC.
ETTL flash with the camera in Manual
with Auto ISO is "auto-auto"... It's two different AE modes. While probably not as unpredictable as "triple auto", it still might do weird, unexpected stuff. I have no idea, because I'd never use more than one AE mode at a time.
BebuLamar wrote:
In auto ISO and when the camera detects there is the flash on it fixes the ISO to 400. So no Auto ISO with flash.
I didn't know that! (As I said, I've never used Auto ISO with ETTL flash.)
This is even more reason to simply turn off Auto ISO when using ETTL flash (either FILL or FULL), if leaving it on forces you to use ISO 400. That's a limiting factor and may not be the ISO you wanted.
To recap:
1. Pick whether you want ETTL "FULL" flash or ETTL "FULL flash". If you want FILL, set the camera to Av, Tv or P auto exposure mode. If you want FULL, set the camera to M exposure mode, but be aware it's still "AE".
2. Don't combine AE modes unnecessarily. That can cause unexpected actions, such as you've seen. Besides Av, Tv, and P.... M with Auto ISO and M with ETTL flash are also both AE modes.
3. I can't see any situation where it would make sense or be useful to use Auto ISO with ETTL flash (especially in light of the above).
Finally, with FULL flash you control exposure primarily with lens aperture and the camera's ISO settings. Up to the camera's flash sync speed (1/180?), shutter speed doesn't matter much, although you can use it to control the "mix" of ambient light with the flash. A fast shutter speed and/or lower ISO setting can be used to make a background go dark, by recording less ambient light. Conversely, slower shutter speed and/or higher ISO can increase background appearance in an image. Regardless how the camera is set, the short duration of FULL flash actually acts like a shutter speed, typically about 1/720.
If using a shutter speed above the camera's flash sync speed, you have to use the flash's High Speed Sync (HSS) feature... This significantly reduces the duration of each flash and, in turn, the distance the flash will reach.
If using slow shutter speeds and flash with moving subjects, such that there will be a mix of ambient and flash light, use the flash's Rear Curtain Sync feature.... this makes "light trails" appear more normally, behind the subject. If Rear Curtain Sync isn't used, the light trails will make a moving subject appear to be moving backward!