Combining ambient light with flash

[Vertigo]

I asked this a while back on the TP forums but it's still confusing me.

Was up at the NEC today taking a few snaps. In situations like this there's some ambient light indoors but not usually enough to get by without flash. I therefore want to supplement the ambient light with a bit of help from the flash so I use fill flash mode, but this is where my problems start.

If I set the camera to Av or Tv, it goes into fill-flash mode and meters for the ambient light without any consideration for the effect of the flash. This will typically leave me with shutter speeds which are far too low, exactly the situation I wanted to avoid by using the flash. My big question is, what's the best way of remedying this? I basically resort to full manual and end up guestimating the exposure I need to get a good ambient/flash balance but, invariably, I find myself taking loads of shots at all sorts of different exposures and also fiddling with flash exposure compensation too until I get a decent shot.

Surely there has to be a better way than this? What techniques do others here use in such situations?

 

[aztechnology]

What camera are you using? I know that Canon cameras meter differently in Av Tv when using flash.

Best bet is to go full manual, most modern cameras will cut flash power when the correct exposure is reached.

 

[Vertigo]

What camera are you using? I know that Canon cameras meter differently in Av Tv when using flash.

40D. Thing is, they don't meter differently - in Av or Tv modes they meter for the ambient light in exactly the same way as if a flash wasn't present.

 

[Messiah Khan]

40D. Thing is, they don't meter differently - in Av or Tv modes they meter for the ambient light in exactly the same way as if a flash wasn't present.

You'll need to go into the camera menu and set the flash settings to something like TTL. The camera should then take into consideration the flash when working out the exposure.

 

[asim18]

Use Manual mode and underexpose your shot.

The amount you underexpose by determines how much flash will be used.

The more you underexpose, the more flash will be used, and ambient lighting will be overpowered by the flash.

The closer you are to the "0" on the exposure meter, the less flash power will be used, and ambient lighting will be more prominent.

This is how it works on my Nikon.

 

[p0ss3s3d]

^
This. Set the exposure of the ambient light and ETTL does the rest (you can add exposure compensation if you wanted)

If your working in low light and want as much ambient as possible set the camera to 1/80th, ISO to 400/800 to obtain a clean shot but you needed to you could go higher, then aperture to f4 (perhaps even f2.8 or f8 if you have DOF requirements)

 

[Vertigo]

Yeah that's basically what I'm doing, using manual to effectively underexpose for ambient light and relying on the ETTL flash to compensate accordingly. I just wondered if there was a better (simpler) way?

 

[vcl_X1]

Perhaps this will help you...

The flash exposure is affected only by the aperture you set.

The ambient exposure is affected by both the shutter speed and the aperture.

For the same shutter speed the wider the aperture the stronger the flash appears (until ttl kicks in and extinguishes the flash, also saving battery power) and the smaller the aperture the weaker the flash appears.

 

[Raymond Lin]

Shoot manual, let ETTL deal with the exposure of the foreground subject and use the ISO and shutter speed to control ambient light.

Aperture will control 2 things with flash, the amount of power the flash uses to light the foreground subject and depth of field. If you are shoot a long shoot with flash the former is more important.

 

[Vertigo]

Ok thanks, looks like I was right to be using manual all along then - probably just need a bit of practise to know what combination of settings I should be using in a given situation so I end up experimenting less

 

[vcl_X1]

Ok thanks, looks like I was right to be using manual all along then - probably just need a bit of practise to know what combination of settings I should be using in a given situation so I end up experimenting less

Partly, you may be able to use some auto, assuming you want to use mainly the ambient I set between -1/3 and -1 2/3 stop adj to ttl on an SB-900, and either manually meter the ambient or use a prog mode for the camera itself, perhaps the Canon flashes have a similar function.

Manual and practice is also a good way to go

 

[robmiller]

probably just need a bit of practise to know what combination of settings I should be using in a given situation

Just dial in the exposure for the ambient—it typically doesn't matter if the resultant shutter speed is long, because your flash will freeze motion. You can usually just set-and-forget.