Underexposing background Query

hemeravisuals

hemeravisuals

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Hey guys i used to know how to do this but i have forgot one of the steps.

Say i want to under-expose my background and my Correct Ambient reading is 1/60th @ F8 I know that to under expose it I would set it to 1/125th @ f8 to cut out a stop of light.

My problem comes with the flash. Do i meter the flash at 1/60th (Original Correct exposure) or underexposed exposure at 1/125th ?
 
I'm no expert but if the flash is set to ettl then it will sort it for you regardless of your settings
In other words I'd meter at 1/125
 
Shutter speed has no effect on the flash exposure. In this scenario, set the flash to be correct at f/8, then adjust the shutter speed to under or over-expose the ambient as you want. It's easiest to adjust this kind of thing by taking a test shots and checking the LCD.

Bear in mind that your max x-sync speed is 1/250sec, so depending on the level of ambient light and how much under-exposure you want for the background, you may need to set f/11 (or lower ISO) to keep the shutter speed below that.
 
You've got two ratios to consider - 1 at the subject and the other at the background.

To underexpose the BG by 1 stop it is the total illumination during the shutter speed that will determine the exposure. Assuming that the ambient is equal over the whole scene I would meter at the subject and then use the distance between the subject and the BG and the inverse square law to 'remove' flash at the background. This does of course assume that the colour balance is all OK between ambient/flash and that there is space to do it.

This is where having a light meter that will show you the mix of ambient/flash is really useful !
 
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