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Forums Lobby GENERAL FORUMS New to Photography (Public) topic #9343
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Subject: "Exposure and Flash Compensation" Previous topic | Next topic
sjcampbl Registered since 10th Oct 2012Mon 22-Oct-12 08:33 PM
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"Exposure and Flash Compensation"


US
          

I'm trying to understand exposure and flash compensation. Specifically, are they separate or associated?

For example, if I use iTTL flash and reduce exposure by 1 stop without touching flash exposure compensation, is just the background exposure adjusted or is the flash (key) exposure also adjusted down by 1 stop? If so, do I always have to reduce exposure and increase flash exposure if I want to maintain proper flash exposure on my subject while under-exposing background?

  

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blw Moderator Awarded for his high level of expertise in various areas Nikonian since 18th Jun 2004Mon 22-Oct-12 11:59 PM
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#1. "RE: Exposure and Flash Compensation"
In response to Reply # 0


Richmond, US
          

There are two completely separate metering operations when we do through-the-lens flash: ambient and flash. You can see the ambient one in the viewfinder. (It's often showing severe underexposure.) This is how the background part of the frame will be rendered. Then there is the flash exposure, which is dominated by the primary subject. This is usually determined by the AF focus point, or at least biased that way. No matter what the ambient exposure, the flash exposure is metered to "properly" expose the main subject.

Each of the metering operations has exposure compensation, and they are cumulative. If you dial in -1 stop of exposure compensation (on the camera), that affects BOTH of them. (I suspect you know this, but in the New to Photography forum, likely few others do.) If you then "reverse" the flash exposure by dialing in +1 stop on the flash, the main subject will be exposed at -1 stop + 1 stop = 0 stops off, while the background (ambient) will be -1 stop.

Used properly, this is another way to make a subject "pop" off a background, even if it otherwise might not, for example if the lens is stopped down, or if it is of similar color to the background.

Note that the above applies to Nikon's iTTL (and older dTTL). I'm pretty sure that Canon's eTTL is set up somewhat differently, although the same net effects can be achieved with either system.

_____
Brian... a bicoastal Nikonian and Team Member

My gallery is online. Comments and critique welcomed any time!

  

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John Bertotti Silver Member Nikonian since 01st Jul 2012Tue 23-Oct-12 01:45 AM
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#2. "RE: Exposure and Flash Compensation"
In response to Reply # 1


Garretson, US
          

I knew none of that! Thanks!

Visit my Nikonians gallery.

  

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sjcampbl Registered since 10th Oct 2012Wed 24-Oct-12 04:05 PM
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#4. "RE: Exposure and Flash Compensation"
In response to Reply # 1


US
          

> -1 stop + 1 stop = 0 stops off

I think that's what I was after. Thanks. I came from Canon Rebel which I believe is different... -1 stop exposure comp +1 stop flash comp = +1 on subject.

Thanks also for the CLS link.

  

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suzyk Silver Member Nikonian since 13th Dec 2011Tue 23-Oct-12 08:21 AM
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#3. "RE: Exposure and Flash Compensation"
In response to Reply # 0


near Hobart, AU
          

Shawn,

Russell McDonald has a great series at Nikon CLS Practical Guide

Cheers,
Suzy

Visit my Nikonians gallery.

  

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