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Old Dec 16, 2007, 10:01 AM   #1
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Just purchased a second hand LN- Nikon 200, a Nikkor 50mm lens and a 10-20 sigma. Great pictures during the day.

I had a hard time yesterday tweakng the camera for a correct picture at dusk.

I popped out the onboard flash, and took the picture, but I still had to set the ISO to 800 to get a clearer picture. I had no tripod to lower the speed. The Sigma open a 4 / 5.6. Of course not very fast, but not a very high number.

Despite the flash, light was very poor and a huge noise appeared.

1- I do not understand why I have to set the ISO to 800 if I am using the flash. Subject was at a distance of about 4 meters

2- Yes, I could set everything on automatic but this is not whatI want.


I would have done better with a webcam :-) So of course I am doing something wrong !

Thank you

Phil
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Old Dec 16, 2007, 10:18 AM   #2
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philgib wrote:
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I would have done better with a webcam :-) So of course I am doing something wrong !
Yes, you are doing something wrong.

That photo was taken using Aperture Priority with the aperture stopped down to f/13. That's not going to let much light in. ;-)

That was taken at ISO 640. But, even you would have been using ISO 800, your flash range would have only been around 2.5 Meters with the built in flash, with your aperture closed down that small (f/13).

The GN (Guide Number) of the built in flash on your D200 is 12 Meters at ISO 100.

To determine maximum flash range, divide the GN by the Aperture.

For example, 12 Meters (the GN of the flash) / 13 (your f/stop) = 0.92 meters maximum flash range at ISO 100.

Then, each time you double the ISO speed, flash range increases by 1.4x.

If you were 4 meters away, you were well outside of the maximum flash range shooting at f/13 and ISO 640.

Either open up your aperture (use a smaller f/stop number) or buy a more powerful flash.

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Old Dec 16, 2007, 10:37 AM   #3
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Thanks Jim. I did not know about this Flash number / ISO rule. I will definitely open the aperture to the max next time toconservea largerGN.

Do you think that going higher in the AV would have also made the trick and allow me to stay in lower ISOs ?

Thx again

Phil
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Old Dec 16, 2007, 10:46 AM   #4
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You need to use a smaller f/stop number (wider/larger aperture opening).

Yes, you could have used lower ISO speeds.

For example, your flash range would have been approximatly 4.2 Meters at f/5.6 and ISO 400.

Also, using an aperture that small (f/13) is going to result in softer photos due to diffraction at 18mm with some lenses. You're going to have pretty good DOF anyway framing that way with an 18mm lens. I wouldn't use apertures that small for those types of images.

But, if you're going to take those types of photos often, buy an external flash.
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Old Dec 16, 2007, 11:06 AM   #5
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Very much appreciated thank you

Phil
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