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Subject: "A question about flash compensation" Previous topic | Next topic
Wingman Silver Member Awarded for sharing his excellent work and continued contribution to the forums, most notably at the Aviation forum. Nikonian since 02nd Dec 2002Wed 13-Nov-13 05:21 AM
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"A question about flash compensation"
Wed 13-Nov-13 05:27 AM by Wingman

Kimberley, CA
          

I am a fairly infrequent user of flash, but there are situations where it is needed, obviously. I use a D700 and D800, and have an SB-800 and SB-600.

One situation where I do sometimes need flash is for outdoor fill. From reading Russ's series, I know to use P mode -- I've actually found this out myself by shooting in my usual A mode but with flash and overexposing stuff pitifully. So P mode and iTTL-bl it is. Supposedly the camera reads the ambient and the flash automatically adds some fill. How much does the flash add, and does this amount vary under different conditions? If so what determines just how much the flash is adding? How much of the frame must be occupied by the shadowed area for the flash to work properly? (An example would be a person 10 feet away with her face shadowed by a cowboy hat or baseball cap, shot with a 50mm lens -- can the flash (or camera) read the fairly small shadowed area and figure out how to add fill to it?)

Another question: Does the flash compensation control work in iTTL-bl? If so, and I set say -2/3 EV of compensation does the flash still vary fill according to conditions but with 2/3 stop less than it would have used? Or once I set the -2/3 EV am I at a fixed ambient - 2/3 stop?

I hope these questions make some sense. Even after using these flashes occasionally for 5 years now I find the whole system rather difficult to understand. I do a lot more "shoot, chimp, correct" sequences than I like. It would be nice to have a bit more understanding of and control over this complex system.

Neal Nurmi

---Wingman Photo---

  

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Replies to this topic

ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography Charter MemberThu 21-Nov-13 12:31 AM
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#1. "RE: A question about flash compensation"
In response to Reply # 0


Powder Springs, US
          

Neal,

I'm sorry that someone hasn't caught this earlier. The secret to iTTL-BL, as I understand it, is the wonder of the D series lenses. The flash exposure is not determined by metering the light that is reflected back at the camera. It is based on the guide number. The distance of the subject focused on determines the flash power relative to the ambient light.

Exposure compensation should affect the ambient and flash equally. Of course you can fine tune the flash by dialing in flash exposure compensation on the flash or, if the camera body has FEC, on the body. I prefer on the body, so I can leave all my flash heads set the same, to nominal, so things don't get dicey.

Scott Chapin
Powder Springs, GA, USA
Nikonians Team Member

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberFri 22-Nov-13 02:30 PM
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#2. "RE: A question about flash compensation"
In response to Reply # 0
Fri 22-Nov-13 02:30 PM by Arkayem

Richmond Hill, GA (Savannah), US
          

>I am a fairly infrequent user of flash, but there are
>situations where it is needed, obviously. I use a D700 and
>D800, and have an SB-800 and SB-600.
>
>One situation where I do sometimes need flash is for outdoor
>fill. From reading Russ's series, I know to use P mode -- I've
>actually found this out myself by shooting in my usual A mode
>but with flash and overexposing stuff pitifully. So P mode and
>iTTL-bl it is. Supposedly the camera reads the ambient and the
>flash automatically adds some fill. How much does the flash
>add, and does this amount vary under different conditions? If
>so what determines just how much the flash is adding? How much
>of the frame must be occupied by the shadowed area for the
>flash to work properly? (An example would be a person 10 feet
>away with her face shadowed by a cowboy hat or baseball cap,
>shot with a 50mm lens -- can the flash (or camera) read the
>fairly small shadowed area and figure out how to add fill to
>it?)

Just to add to what Scott wrote. The amount flash power when in TTL-BL mode is determined by two things: 1) the distance to the subject, and 2) the average brightness of the ambient light across the whole frame. If the subject is occupying a large amount of the frame, and the subject is significantly darker than the background, the average brightness of the frame will be low, and the flash power will be low. If the subject is significantly darker than the background, but the subject occupies a smaller amount of the frame (ie., you are farther away), the average brightness of the frame will be greater, and the flash will fire at a higher power. I have found that TTL-BL works best when fairly close to the subject so that the subject occupies about 1/3 the area of the frame. I always keep this in mind when zooming in on the subject.

> Another question: Does the flash compensation control work in
>iTTL-bl? If so, and I set say -2/3 EV of compensation does the
>flash still vary fill according to conditions but with 2/3
>stop less than it would have used? Or once I set the -2/3 EV
>am I at a fixed ambient - 2/3 stop?

The flash ev simply makes the flash fire at a greater or less power than it would have normally. Keep in mind that when shooting TTL-BL outdoors in bright ambient, the flash sometimes does not have enough power to add the amount of fill that is being asked for by the system. In this case, increasing the ev will do nothing, since the flash is already firing at full power.

>I hope these questions make some sense. Even after using these
>flashes occasionally for 5 years now I find the whole system
>rather difficult to understand. I do a lot more "shoot,
>chimp, correct" sequences than I like. It would be nice
>to have a bit more understanding of and control over this
>complex system.

No matter what you do, you will still have to chimp a lot and do post processing. I always did. TTL-BL will brighten the subject enough to be usable, while allowing you to shoot rapidly and in changing light conditions. It will usually get close enough to be adjusted in post processing to look perfect.

I usually used -.7 ev when shooting flash (TTL or TTL-BL), so that I would underflash a bit rather than blow something out. You can brighten underflash during post processing quite easily, but you can't fix a blow out.

Russ
Nikonian Team Member
Russell MacDonald Photography
Nikon CLS Practical Guide

  

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Wingman Silver Member Awarded for sharing his excellent work and continued contribution to the forums, most notably at the Aviation forum. Nikonian since 02nd Dec 2002Fri 22-Nov-13 07:31 PM
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#3. "RE: A question about flash compensation"
In response to Reply # 2


Kimberley, CA
          

Thanks for the replies -- this helps, I think.

Though if Russ does a lot of chimping while shooting fill flash, it makes me feel a little bit better...

Neal Nurmi

---Wingman Photo---

  

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