Using fill-in flash

[aeronic]

I was trying to take some photos last night of my niece (2 yrs old) in a well lit room with a Canon 550D and 50mm f/1.8.

However, when I set the camera to aperture priority (and used f/1.8 with iso 1600) the shutter speed was a bit too slow (1/60th) for the situation.

However, when I set the camera to Program mode (using f/4, ISO 400 and flash), the picture was a bit 'flash white'.

I would like to use the onboard flash as a fill-in flash, with settings somewhere between the two (ie f/2.2 and ISO 800 with a bit of flash to achieve 1/100th or so). I tried to 'dial it down' on the flash exposure compensation, but at -2ev and -1ev the photo just looked dark (as if I had changed the actual exposure).

Any hints or suggestions welcome.

 

[Nawty]

On of the problems you're seeing is the difference in white balance between the flash and the ambient lighting, ideally you would use a flash gel which will sort that out, then your settings will be fine. Or, you could try setting WB to flash and seeing if that helps (background colour will be pretty funky though...

Otherwise I would use manual controls to underexpose by half a stop or so and use the flash for the last bit.

 

[HoppyUK]

Stick with Av.

If you want fill-in flash, then the starting point has to be the ambient light, which is hardly well lit of it's metering at 1/60sec at f/1.8 with ISO1600. But in terms of exposure at least that's not an issue and you just have to balance the flash with it (though you may have problems with focusing, movement and noise).

Use the independent compensation controls for flash and ambient light to get that how you want, as it sounds like you have been trying, but if you then set (as you say) 1/100sec at f/2.2 at ISO800 you will have taken about almost three stops out of the ambient exposure which will make it very dark, and then you've dialed the flash down so obviously that's going to be dark too.

 

[aeronic]

I think I have the solution to my problem - M mode!

The issue was that I couldn't select 1/100 f/2.2 using simply P or Av mode - I needed to use full Manual. I've done a bit of testing today (indoors) and come up with some really interesting theories...

 

[aeronic]

follow up...

I tried a test scenario with a static subject, using ISO 400 constantly throughout to eliminate that variable.

From 1/30 at f/1.8 up to 1/125 at f/1.8
then 1/15 at f/2.8 to to 1/60 at f/2.8
then 1/6 at f/4.0 to 1/25 at f/4.0

All photos were similarly exposed - with the flash compensating for the two stops of difference between lightest and darkest.

I now understand the process quite a lot more.

Is it possible to read from EXIF data the power output of the flash on any given shot? (ie 1/64th etc)

A further test shows that I was also able to get similar exposure at f/16 and 1/200th (which is 5 stops darker still)

 

[troutfisher]

A suggestion,if you are going to be playing a lot with flash both indoors and outdoors treat yourself to a speedlight either a 430 or a 580 depending on budget.
A used 430EX Mk1 will cost about £100 its more than adequate and the difference between a dedicated flash and the onboard flash is chalk and cheese.
The main difference which you would see immediately is the ability to bounce the light off walls and ceilings,makes a world of difference.
Google 'Canon Flash Bible' and have a read it opens up a whole new world.

 

[ohara]

P mode is great for beginners with flash as you literally can't get it wrong. Note that P mode will use the flash for fill if the background is light enough, but if it's not it will use the flash to expose the subject and sacrifice the background. It will never go slower than 1/60 (you need to use Manual if you want to do that).

Also, shutter speed has no effect on flash exposure as the shutter is open for FAR longer than the flash emits light. Aperture on the other hand has a direct impact on flash as it's changing the amount of light which gets into the lens. The more you stop down the aperture, the more power the flash has to use to expose correctly.