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Old Nov 25, 2005, 7:13 PM   #1
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I am having a hard time understanding just how flash (both with the pop-up and camera-mounted 380EX Speedlite) works on my 20D, especially in Creative Modes.

In AV or TV mode, the camera appears to choose the same exposure settings regardless of whether the flash is activated or not. Is this correct? If so, I would love a clear explanation of how to use flash with the Creative Modes. I am actually having more success using AE program mode when using flash. What am I missing?

Thanks!


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Old Nov 25, 2005, 9:16 PM   #2
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http://photonotes.org/articles/eos-flash/

Far more info than you're looking for certainly, butnicely indexed so finding particulars isn't too tuff.
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Old Nov 26, 2005, 1:27 AM   #3
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Gordon, in AV and TV modes the camera sets the exposure as if the flash were not on. This exposure reamins that way and the flash is used as a fill flash. In program and auto modes the camera and flash create an exposure for the flash to work as the main light source. I believe that's it in a nutshell.

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Old Nov 26, 2005, 8:22 AM   #4
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On the Canon cameras you should use the manual mode (M) and control both the shutter and aperture - the flash remains on automatic and will expose properly

-> you can vary the fill by judging the -2..-1..v..+1..+2 scale on the bottom of the viewfinder this way :idea:
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Old Nov 26, 2005, 12:24 PM   #5
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Thanks! for all the above answers - they were all very helpful.

NHL: At first I didn't quite get what you were suggesting, until I tried the Flash ExposureCompensation button. This combination of Manual mode + FEC seems, so far at least, to be what I have been trying to obtain with my flash pix. Thanks so much!! :-D
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Old Dec 1, 2005, 1:27 PM   #6
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gordonj wrote:
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I am having a hard time understanding just how flash (both with the pop-up and camera-mounted 380EX Speedlite) works on my 20D, especially in Creative Modes.

In AV or TV mode, the camera appears to choose the same exposure settings regardless of whether the flash is activated or not. Is this correct? If so, I would love a clear explanation of how to use flash with the Creative Modes. I am actually having more success using AE program mode when using flash. What am I missing?

Thanks!

What NHL said was right on, but just to clarify: When using flash, use P or M. When using P, the camera exposes automatically for the flash. Meaning, your subject or foreground will be properly exposed, while your background may not get any "flash" at all, and therefore be very dark. This is the easy, less attractive method to usng flash.

A better method is to use flash in M mode, and think of it this way. There are 2 exposures in the one shot: The flash automatically properly exposes the subject, and this is mostly independent of the shutterspeed/aperture you choose. Then for the background, set the manual exposure settings to expose the background. You can point the camera towards the background, get a reading by half-depressing the shutter, and set the aperture/shutter speed accordingly. A good place to start would be to set the exposure at -1EV. This will give you some background, but the foreground/subject will stand out.

You can experiment with this in your house at night. With the flash on, choose M mode, and set an aperture of 2.8 (or your widest aperture), and set the shutter speed to 1/60. No matter how dark or light the room is, the flash will properly expose your subject. Change the shutter speed, and the foreground exposure remains constant, but you get more or less light in the background.

Also note that the wider the aperture, the more effective the flash will be (or the greater distance it can cover). Also, increasing youer ISO setting will allow you to get more exposure for dark backgrounds (assuming the same exposure setttings) when using this method.

Finally, this method I describe is just as useful outdoors during the day (AKA "Fill Flash") , when you want to your make your subject pop. Keep in mind that in daylight, you will probably need a flash with "high sync mode" as your shuter speeds outdoors will be greater than 1/200. This with a wide aperture for background blur produces a really cool effect.

So to summarize, think of a flash shot in M mode as 2 separate exposures. The flash exposure is handled automatically and exposes the forefround. Then you pick the background exposure by tuning the aperture, shutter speed, and ISO.

Hope this helps.

Here's an example using this fill flash method outdoors. This was taken on a bright sunny day, underneath a shade tree. I underexposed the background and let the flash light the subject. I was experimenting with a diffuser here as well, which gives the "light from above" look. Also notice the fast lens (2.8 aperture) gives the background the nice blur:



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