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Flash Exposure Differences

bobcowin

New York, US
4 posts

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bobcowin Registered since 05th Jan 2008
Thu 13-Dec-12 05:06 PM

I am using the D800 with a SB-910 flash. I've been taking photos at a couple of evening parties recently, so I set the camera to manual and set adjustments to get a little ambient light (ISO 640, 100th, f4.5 or there abouts). The flash is set to TTL and has the supplied dome as well as the tougsten "gel".

If I have the flash at 90 degrees (pointing stratght ahead) the subjects in the images tent to be underexposted by just over 1/2 a stop. If I turn the flash head up to 70 degrees or so, it does a much better job of exposing.

I am thinking that when it's straight ahead, maybe the camera simply uses the distance info from the lens to calculate how much flash to use, and when its's up, it depends more on the TTL readings?

I'm probably not doing anything right, but can anyone explain why I'd be getting such different results?

Thanks.

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klrbee25

Naples, US
1386 posts

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#1. "RE: Flash Exposure Differences" | In response to Reply # 0

klrbee25 Silver Member Nikonian since 03rd Jun 2006
Fri 14-Dec-12 01:29 AM | edited Fri 14-Dec-12 01:30 AM by klrbee25

When you say 'the images are underexposed by 1/2 a stop', do you mean the subject or the ambient background? Flash photography is essentially two exposures (ambient and subject), so I want to be sure I'm understanding correctly.

Maybe post a couple examples too?

If you're enjoying flash photography, this website will be your new guilty pleasure...
www.neilvn.com His articles are what you want to check out.



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bobcowin

New York, US
4 posts

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#2. "RE: Flash Exposure Differences" | In response to Reply # 1

bobcowin Registered since 05th Jan 2008
Fri 14-Dec-12 10:19 PM

The subjects are underexposed. It was a week ago, but I beleive the first image was taken with the flash angled up, the second stratight ahead.

Click on image to view larger version


Click on image to view larger version


Attachment#1 (jpg file)
Attachment#2 (jpg file)

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avisys

Placitas, US
482 posts

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#3. "RE: Flash Exposure Differences" | In response to Reply # 2

avisys Basic Member
Fri 14-Dec-12 11:11 PM

???????

The shadows under the subjects' chins, and the background exposure, suggest that the flash position might have been the same. ?????

Why manual? For informal stuff, such as parties, I love letting the camera do its thing, and the exposures with flash are virtually always right on, or close enough for the event. And you end up with so much freedom to not worry about exposure in this corner, and then exposure in that corner, and then over in the kitchen, etc., etc.

The D800 has a million dollar meter; I love letting it do its work. I mean, after all, I paid for it!



AviSys

klrbee25

Naples, US
1386 posts

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#4. "RE: Flash Exposure Differences" | In response to Reply # 2

klrbee25 Silver Member Nikonian since 03rd Jun 2006
Sat 15-Dec-12 01:35 AM

I agree these look both look like 'head on' flash directed right at the subjects. The underexposure can happen if you're shooting quickly at full power and the flash hasn't recycled.

With TTL, the reflectivity of your subject will impact your exposure and the camera's adjustment of flash power. What are your settings? Do you have AutoFP enabled? While Nikon's TTL does a pretty darn good job, you need to adjust the flash EV compensation to correct variations in flash exposure. It's still not a set and forget system.

What is the EXIF info for the photos?

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icslowmo

Surprise, US
613 posts

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#5. "RE: Flash Exposure Differences" | In response to Reply # 2

icslowmo Registered since 01st Jan 2012
Sat 15-Dec-12 08:34 AM | edited Sat 15-Dec-12 08:46 AM by icslowmo

Looking at these two shots, I would agree the flash angle seems the same. But sense one person is different between each shot, I would imagine the flash had plenty of time to re-charge.

Now the difference between these two shots, the first woman had a very reflective top on and reflected much more light back at the camera/TTL exposure system causing the under exposure. The second woman was wearing a black top so the TTL system would metered a higher flash power. Hope this helps.


Chris

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ajdooley

Waterloo, US
3321 posts

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#6. "RE: Flash Exposure Differences" | In response to Reply # 0

ajdooley Gold Member Nikonian since 25th May 2006
Sat 15-Dec-12 10:24 AM

Bob -- I agree with letting the camera do the work for you - especially in situations like your photos -- a party where you are shooting a lot of photos at short to medium range. Set the mode on "P", ISO 800 or so and fire away. If you are using TTL/BAL on the flash, even foregrounds and backgrounds will be balanced in most cases. It's the results that count -- not how hard you work!

Alan
Waterloo, IL, USA
www.proimagingmidamerica.com

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klrbee25

Naples, US
1386 posts

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#7. "RE: Flash Exposure Differences" | In response to Reply # 6

klrbee25 Silver Member Nikonian since 03rd Jun 2006
Sat 15-Dec-12 02:36 PM | edited Sat 15-Dec-12 02:37 PM by klrbee25

I really hate how the camera manages settings when using flash. In any dimly lit environment, it will start maximizing ISO and aperture to allow in ambient light. You'll end up with every shot taken at your minimum flash shutter speed, maximum aperture and highest ISO (if using AutoISO). I much prefer the additional control of using Manual mode with flash. I've been doing a lot of 'studying' with regards to flash photography lately. Using the cameras programmed mode with flash is akin to using the old 'Landscape', 'Portrait', 'Fireworks', etc modes of cheaper cameras. You have a great set of gear...learn to maximize it's capabilities.

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ajdooley

Waterloo, US
3321 posts

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#8. "RE: Flash Exposure Differences" | In response to Reply # 7

ajdooley Gold Member Nikonian since 25th May 2006
Sat 15-Dec-12 04:51 PM

I just shot a job yesterday -- Santa and kids, with a window lighting from Santa's left (camera right). I shot in P mode and TTL/BAL setting on the flash -- ISO 800. I was able to devote my attention to the kids vice lighting. The most adjustment required in CS6 on the raw images was .3 f f/stop. Some kids have lighter ior darker complections. I don't use auto ISO. But this again -- as usual -- gave me results that sold and will make good money. And the photos were really very nice. I do make manual exposure adjustments when that provids the best results -- I have learned when to and when not to.

Alan
Waterloo, IL, USA
www.proimagingmidamerica.com

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Clint S

Chula Vista, US
460 posts

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#9. "RE: Flash Exposure Differences" | In response to Reply # 0

Clint S Silver Member Nikonian since 02nd Jan 2011
Fri 21-Dec-12 06:47 AM

When moving around and not sure where my subjects may be located I'll typically use Aperture priority and set my ISO at 400-1250 depending on the available light.

And then using TTL, with either Nikon or Qflash, I get more consistent results using spot or center-weighted metering along with AFS single point or AFC 9 point focusing. Nikon's seem prone to weight exposure on the focus point.

If I can't bounce a Nikon flash then I'll aim it up at 30-60 degrees with the dome.

I just do not seem to get consistent results when using matrix metering and 3d or auto area focusing.

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