Getting to grips with built-in flash

[celtex]

Hi All, I have been trying to understand something on my 600D:

In P mode (which I have hardley used) the BI flash pops up when needed, everything is set automatically and results are good.

But in Av mode I am nost sure what is happening, as an example, say I am in low light conditions (flash down) and set the aperture to say 5.6, or the lowest it will go to for a given setting/lense/iso etc - I might get a shutter speed of 0"3, or 1"3 - so if I want to keep the iso and cannot increase the size aperture, I pop the flash.

But, this does not seem to auto sync the shutter speed, to take account of the flash now being deployed. instead, it seems that the shutter speed stays the same, so let's say it was 1"3 - and what happens next is I take the shot, the flash fires and the shutter stays open for the long time it was set at. So the flash is acting in addition to the settings, not taking control and changing the shutter speed?

I read in the manual that the shutter sync speeds are between 1/60th and 1/250th (or similar, not got it in front of me so cannot remember precisley) but the point is there is a range, so why does it not alter the ss in Av mode?

Is it just thinking that I want 'fill-in' flash (something else I don't understand is how it works out when to add supplimentary lighting as opposed to full power).

If I do the same in Tv mode, lets say I have a SS of 1/400 (I just tried this) and my aperture light is flashing, telling me to open it up, so I depoly the flash, and this time my SS dropped to 1/200th (maybe I moved the camera a fractrion) - but the ap is still flashing - the little lightning icon is lit to tell me the flash is ready and waiting to go. Obviously in Tv mode I want to be in control of the ss, but it does not seem to adjust the aperture to take account of the flash.

what am I missing, what do I need to understand?

Thanks

Ian

[briansquibb]

Re: Getting to grips with built-in flash

Ian,

In AV mode the flash is used as fill - so the apperture stays at the same as you have fixed

In TV mode the you set the shutter speed so the flash tries to give you enough light. In your case the maximum sync speed for the popup flash is 1/200 so the camera reduces it so you get a shot.

In M mode you set the shutter and apperture so the flash adjusts itself to that

Some high range external flash units (such as the 430EX and 580EX) have another feature called high speed flash which allows flash sync up to 1/8000 - albeit at reduced power.

Brian

[Trevoreast]

Re: Getting to grips with built-in flash

But, this does not seem to auto sync the shutter speed, to take account of the flash now being deployed. instead, it seems that the shutter speed stays the same, so let's say it was 1"3 - and what happens next is I take the shot, the flash fires and the shutter stays open for the long time it was set at. So the flash is acting in addition to the settings, not taking control and changing the shutter speed?

Ian this is a very common problem. At it's root is that that the ambient light and the flashlight are metered separately.
Thus the camera won't take account of the flash to give you a faster shutterspeed for your choosen aperture in AV mode.

Trev

[celtex]

Re: Getting to grips with built-in flash

Thanks Guys,

seems I have quite a bit to learn about flash


Ian

[gibsonk]

Re: Getting to grips with built-in flash

Ian,

I am not sure on the 600D however certainly on the 40D you can fix the Flash sync speed in the custom functions when in Av mode.


Update you can on the 600D see below

Custom Function

C.Fn1-3 you have 3 options

0=Auto
1=1/200 - 1/60 sec (Auto)
2= 1/200 Fixed

[celtex]

Re: Getting to grips with built-in flash

Thanks again, found those custom settings and been looking through all the links from above

Cheers all - I have a lot of reading to get through!

Ian

[Trevoreast]

Re: Getting to grips with built-in flash

I would leave that CF setting on the default if I was you Ian

Changing it isn't going to give you a faster shutterspeed in AV mode in low light.

On a bright day when the camera's ambient light meter suggests: ISO 100 F5.6 1/800.
Soon as you pop up the flash for fill flash, the camera will slow the shuttersppeed to it's max sync speed which is 1/200
All you can do to avoid over exposure is stop your lens down to a narrower aperture given that ISO 100 slowest (least sensitive) on you camera. As Brian says with a 4 or 5 series flashgun you can use high speed sync.

In the above situation, you could add a filter to limit the amount of light coming through the lens, but that's another story.

Your question is pretty wide ranging, which is OK but you may be better narrowing your question by asking about a specific lighting environment in a particular camera mode. I say this to help.

Trev

[briansquibb]

Re: Getting to grips with built-in flash

I echo Trev's comment about the setting - leave it on default.

I often have my flash on in really bright light to lift the really dark shardows - particularly for people shots. I have a 430EXII for that when on walkabout (less obvious for street work)

[celtex]

Re: Getting to grips with built-in flash

Thanks guys, yes, I found those settings, but have have no intention of altering them!

Thanks to you all, and in particular the article links posted by Dan - I have a much clearer (by no means perfect) understanding of what is going on.

Thanks

Ian

[George Bear]

Re: Getting to grips with built-in flash

Ian

You may also want to look at this three part article in CPN Canon Pro Network - Getting the most from Speedlites.