OCF and AV mode

ronlane · Mar 8, 2013

In order to use (properly) an off camera flash in the Appeture priority mode, do you need to have TTL for the flash?

As I am learning, my thought would be yes because without it, the camera will set the ISO and shutter speed for the darker conditions and when it flashes you will get a blown out picture.

Am I thinking correctly here?

tirediron · Mar 8, 2013

The best way to use OCF is in full manual. If you specifically wanted to use AP, then yes, you would need TTL, but I can't envision a circumstance where you would need/want to use AP.

ronlane · Mar 8, 2013

I was watching a B&H training video where it was talking about AV mode and it got me to thinking about using it and a flash. But I was thinking that I would need TTL in order to use them together.

(It's one of those thoughts that goes through my head while I'm at work, thinking about photography)

Thanks Tirediron

tirediron · Mar 8, 2013

I suppose if you were using i/eTTL and CLS/Canon equivalent, you could, but I still can't imagine why you would...

ronlane · Mar 8, 2013

fair enough. I won't be trying it because I don't have i/eTTL and I mostly use manual mode. No real reason for wanting to use it other than to be lazy about the settings when taking pictures.

bratkinson · Mar 9, 2013

I'm a 'try it and see what happens' type of person...OK..."experimenter", if you will. This is especially true with digital photography as it costs nothing to take a shot and whatever settings I think are 'right'.

If needed, I'll take a number of shots 'bracketing' shutter speed, aperture and even ISO and pick the winner...if I have time. Obviously, 'trial and error' at a wedding, for example, won't work due to available time for once-in-a-lifetime shots (or twice, or thrice...)

Overread · Mar 9, 2013

The thing is even if you have Ettl the camera can still only meter based on ambient light, if flash is just for fill lighting then you'll be ok, but if its the main light then AV mode is just not going to work because it will keep reading the darker ambient lighting present and setting its shutter speed based off that.

The only way you can meter with flash light pre-shot is to use an external lighter meter which can read the light fired off by the flash (for which you can also use it to record the incident light (that is the light before it hits the subject) instead of the reflected light that the camera naturally picks up.

Robin_Usagani · Mar 9, 2013

You can kinda do it. Set it to AV and set it at -2 exposure compensation. Then power the flash in manual until your subject is at right exposure. But then if the subject change clothes, you change the sampling area of the meter, change background... You wont get consistent results.

EIngerson · Mar 9, 2013

Yes, you would have to be in TTL most of the time. Most of the time high speed synch is also required and set your camera to trigger on second shutter. Like Robin said, your metering is going to jump all over the place.

Mike_E · Mar 9, 2013

You need to mesh the flash's output to the aperture setting on your camera. No matter which mode you use. (leaving off shutter speed mode- which will only make your life miserable)

If you're in Av you set the f-stop and adjust the power of the flash to suit. The camera will meter the scene and adjust the shutter speed for the ambient. The only thing that matters for what you light with the flash is matching the output of the flash with the proper aperture setting- shutter speed has no real effect on the subject.

To control the exposure of the background you'll need to be in manual as the shutter speed does control that unless you're lighting that too.

Look up dragging the shutter.

cynicaster · Mar 9, 2013

ronlane said:
In order to use (properly) an off camera flash in the Appeture priority mode, do you need to have TTL for the flash?

As I am learning, my thought would be yes because without it, the camera will set the ISO and shutter speed for the darker conditions and when it flashes you will get a blown out picture.

Am I thinking correctly here?

The camera won't touch the ISO setting in Av mode, unless you have Auto ISO enabled.

If your subject does get blown out using this approach, it's not because the camera selected a long shutter speed. The duration of a flash is something on the order of 1/10,000 of a second, meaning it will have the same lighting effect on the subject regardless of whether the shutter is open for 1/10 of a second or 1/250 of a second. What will change (dramatically) in those two scenarios is the exposure of the background.

I see no reason why it wouldn't be possible to work some trial and error on aperture and flash power to get good results in Av mode, but the lingering question is, why would you want to let the camera set the ambient exposure when you can dial it in yourself in M mode with a few trial shots that cost you nothing?

ronlane · Mar 9, 2013

Thanks for all the reply's. It was something that was just a thought and not really something that I'm set up to do or try because I don't have ttl with my flash triggers.

Cynicaster, I realize that AV doesn't adjust ISO but that would be something that I would need to do myself.

Also, I am not set up for high speed sync either.