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Confused about exposure compensation with flash

Hamslay

UK
115 posts

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Hamslay Registered since 01st Nov 2005
Tue 01-Nov-05 05:00 PM

While I continue to save for an SB-800, I've just bought a LumiQuest Soft Screen to try to calm down the harshness of the pop-up flash. The piece of paper that comes with the device claims that no exposure compensation should be required, but that's just not true. With the Soft Screen in place, pictures are just too dark. Time to tweak...

In the past I've used exposure compensation a fair bit (using the +/- button and command dial), and am used to the camera adjusting the shutter speed or aperture to alter the exposure. I believe one can adjust the power of the pop-up flash using the Flash exposure compensation (flash button and +/- and command dial) to alter the flash power. However, what I did in this case was to just use normal exposure compensation, and expected to see some evidence of the aperture or shutter speed changing, but I didn't. As anticipated, dialing in +2 EV fixed the lighting, but I'm confused just how it did it. The aperture couldn't have opened, as I was already at maximum. The shutter speed didn't seem to change - at least I couldn't hear that it was slower. So I can only guess that the flash power was increased, which would seem a logical way of increasing exposure in this situation. But if exposure compensation adjusts flash power when the pop-up flash is used, what is the flash exposure adjustment for, as it seems to do exactly the same thing!?

I could just leave it that it works, but it bugs me to not know what's going on!

edmun

eugene, US
8618 posts

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#1. "RE: Confused about exposure compensation with flash" | In response to Reply # 0

edmun Registered since 16th Sep 2003
Tue 01-Nov-05 05:50 PM

The problem with the built in flash is that it just does not have much power.

Any diffuser will cut the effective power down. So increasing something that is at 100% just will not work.

bottom line you get a softer image will a lot less range.

ledmun

Hamslay

UK
115 posts

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#2. "RE: Confused about exposure compensation with flash" | In response to Reply # 1

Hamslay Registered since 01st Nov 2005
Tue 01-Nov-05 06:00 PM

For ranges of 5ft - 10ft it seems usable, but only with the exposure increased. Back to the question - how's it doing it!?

edmun

eugene, US
8618 posts

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#3. "RE: Confused about exposure compensation with flash" | In response to Reply # 2

edmun Registered since 16th Sep 2003
Wed 02-Nov-05 06:57 AM

The camera changes the power output of the flash.

ledmun

Hamslay

UK
115 posts

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#4. "RE: Confused about exposure compensation with flash" | In response to Reply # 3

Hamslay Registered since 01st Nov 2005
Wed 02-Nov-05 07:10 AM

So if the pop-up flash is up, changing the exposure compensation changes the flash power. I thought that's what I saw. So what on earth is the flash exposure option for, when "normal" exposure compensation does exactly the same thing????

edmun

eugene, US
8618 posts

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#5. "RE: Confused about exposure compensation with flash" | In response to Reply # 4

edmun Registered since 16th Sep 2003
Wed 02-Nov-05 06:48 PM

The flash comp button changes only the flash power not the main exposure.

ledmun

Hamslay

UK
115 posts

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#6. "RE: Confused about exposure compensation with flash" | In response to Reply # 5

Hamslay Registered since 01st Nov 2005
Wed 02-Nov-05 06:53 PM

Sure, but changing the regular exposure compensation with the flash up only seems to change the flash power too - aperture and shutter speed are unchanged.

Drewhound


121 posts

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#7. "RE: Confused about exposure compensation with flash" | In response to Reply # 6

Drewhound Registered since 01st Mar 2007
Wed 02-Nov-05 10:51 PM

Have you got it set on ISO auto? I wonder if it upped the ISO when you added the compensation

Hamslay

UK
115 posts

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#8. "RE: Confused about exposure compensation with flash" | In response to Reply # 7

Hamslay Registered since 01st Nov 2005
Thu 03-Nov-05 06:49 AM

I'm pretty sure it wasn't on Auto ISO. Also, I was able to step the exposure compensation up several times and each time achieve a better exposure. If the ISO were increasing I would have had at most 3 more exposure options.

Strange. I'll have to get the camera out again tonight and try again.

avm247

Rancho Cordova, US
18632 posts

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#9. "RE: Confused about exposure compensation with flash" | In response to Reply # 0

avm247 Moderator Awarded for high skills in documentary architecture and aviation photography Donor Ribbon. Awarded for his support to the Fundraising Campaign 2014 Charter Member
Wed 02-Nov-05 08:11 PM

Nikon's default flash system is some form of balanced fill flash. If you are getting a pre-flash, you are useing a balanced fill flash mode. In fill flash, the camera is trying to balance both the ambient light and the flash burst. In a balanced fill flash mode, the camera is adding some -EV to the flash.

Adding flash compensation to a balanced fill flash mode will have a cumulative effect and will be unrepeatable unless you are shooting in the exact same conditions (and even then, there may be some variation).

It is best to run a controlled test to verify how the built in flash behaves in manual exposure mode (this should revert to a standard TTL mode). Depending on the lighting conditions, you can add from -.7EV to -2.0 EV to get repeatable results. As you have the Lumiquest diffuser, I recommend running a test with that, too. Note that you will lose power with the diffuser so the flash will not have the same reach.

(In a pre-flash mode, with the Luniquest diffuser, the camera will see that not enough light is reaching the subject and may try to add more light as a result.)

Anthony

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Anthony

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