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 Post subject: TTL flash question !!
PostPosted: Fri Jul 16, 2010 5:37 am 
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Location: Malaysia
i took some pictures in a hall at a wedding...

ive set my ISO to around 800, aperture 5.6 and shutter around 1/30..

why does sometimes the pictures turn out nicely exposed but sometimes, subjects become overexposed or underexposed ??...

what influences the flash or the camera to do that ??

i thought when the ambient light is almost the same, and exposure setting is the same as above, the TTL flash should expose the pic nicely...

please advice..

thanks


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 Post subject:
PostPosted: Fri Jul 16, 2010 8:01 am 
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What mode was the camera in? (full manual, aperture priority etc etc). How close were the subjects to the flash and what other reflective objects were in the shots? The camera knows how much light the flash will add to a shot but not how much of that light will be reflected back through the lens.

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PostPosted: Fri Jul 16, 2010 8:31 am 
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emmmm....

the situation was like this...

i was sitting at the designated table with my family....using manual mode, ive set the ISO, aperture and shutter speed....using TTL flash, i took a pic of the person opposite the table, which came out fine, when i start taking the person 2 seat from me, it came out over and sometimes under exposed.

U were saying something about the flashing knows how much light to add but doesnt know how much reflected back ??...

what does it mean ???...

ive read few books on On camera flash and many tell on the metering and ttl flash will do the rest. But under what circumstances that the TTL flash gets fooled by the ambient light or the situation ??...i hope im making sense, i just donno how to explain my predicament...

thanks for sharing ....

D5ooo


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 Post subject:
PostPosted: Fri Jul 16, 2010 2:00 pm 
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Quote:
U were saying something about the flashing knows how much light to add but doesnt know how much reflected back ??...

what does it mean ???...
I mean, you take a picture of a piece of black paper and you then take a picture of a white piece of paper. The white paper will reflect much more light back towards the camera. The same thing happens with anything in your shot, lots of light wall covering (paint/paper) or light vs dark clothes, a white wedding dress will usually bounce more light than a black dinner suit.

The other thing is you say you were in full manual mode which means you didn't allow the camera to use it's TTL metering to adjust certain settings.

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Nikkor AF-S DX; 18-105 f/3.5-5.6G VR, 55-300 f/4.5-5.6G VR, 35mm f/1.8G
Speedlight SB-700

http://keystrokesukimages.com


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 Post subject: thank you
PostPosted: Sat Jul 17, 2010 3:14 pm 
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Dear keystrokesuk,

thanks for your reply...i will google more about this topic...

lastly, if not manual mode, what mode do you suggest ???...

thanks again..


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 Post subject:
PostPosted: Sat Jul 17, 2010 3:45 pm 
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Manual mode is the mode to use when doing flash photography. You can leave your flash on TTL, and the camera will automatically work out how much flash is necessary.

The reason you want to use manual mode is so that you cut down the number of variables that the camera can tweak to obtain the correct exposure. If you're in Manual mode, the only thing that the camera can tweak to get the correct exposure is the flash power. If you're in P mode with auto ISO, the camera can tweak the aperture, shutter speed, ISO, and flash power. Having the camera change 1 setting vs 4 settings is going to help you with repeatability and reliability.

To better understand how to use your on camera flash, get a hold of the book "On camera Flash Techniques for Wedding and Portrait Photography" by Neil van Niekerk.

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