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PostPosted: Sat Nov 24, 2007 3:39 pm 
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By incident today I shot a sequence of photos with exposure-bracketing left on. It was set to 3 shots -2EV, 0EV, +2EV.
As I tried to save the over and underexposed shots (from RAW in captureNX) I was quite surprised:
- I had one shot at f5.6 1/20 sec, ISO 1600 (!); this was the +2EV over-exposed one. This one was clearly in the danger-zone, ISO-wise.
- and I had one shot at f5.6 1/45 sec, ISO 200; this was the -2EV underexposed shot. This shot had received only half the light of the other shot but was very much in the ISO-comfort-zone.
My assumption now was, when I corrected both shots with +-2EV in CaptureNX that the second shot would turn out fine and the ISO 1600 shot would be lost, due to noise.

Boy was I wrong! On a nice low-contrast patch of background, the underexposed ISO-200 shot came up with very visible noise after correcting +2EV, while the overexposed ISO-1600 shot almost had no grain :shock: :?: :idea:
It just looked like the ISO-values were reversed, so krass was the difference in noise.

The only thing that could not be saved were the highlights from the overexposed shot.

Well, you live to learn :roll:

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PostPosted: Sat Nov 24, 2007 4:19 pm 
Thomas
Can we have a link to those shots ? Am curious also :?:


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PostPosted: Sat Nov 24, 2007 4:48 pm 
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I thought you would say this :wink:

Here's the ISO 1600 shot postprocessed with -2EV:
Image

Here's the ISO 200 shot postprocessed with +2EV:
Image

Beware: you're looking at 100% crops! This is called "pixel-peeping" :wink:
So now these are the first shots with the same camera where the ISO 200 shot has much higher noise than the ISO 1600 shot :? :idea:
If you believe I mixed the photos up, just click through to the flickr-page and click on "more properties"...

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PostPosted: Sat Nov 24, 2007 6:22 pm 
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Thomas!!! tut tut...lol I've done something similar, but i check each shot if I can, or check them after about 10 or so - then i know if i've changed a setting by accident.

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PostPosted: Sat Nov 24, 2007 6:24 pm 
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Wait another 35 years, Daniel and you'll be losing it on some settings too :wink: :D :lol:
At least it gave me a first: more noise on lower ISO 8)

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PostPosted: Sat Nov 24, 2007 7:17 pm 
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Makes sense...


Your trying to Digital Amplify light, just like increasing ISO on the -2ev photo, but on the +2ev, you are Digital De amplifying the light, so it will react as if the ISO setting is going down.

...or at least makes sense to me lol.

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PostPosted: Sat Nov 24, 2007 7:51 pm 
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Yeah, the underexposed low ISO shot got only half the light (1/45 sec vs. 1/20 sec) so in the end there is a 1 stop disadvantage. But still I couldn't believe my eyes, when I saw the results :shock:

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PostPosted: Sat Nov 24, 2007 11:43 pm 
Wow
Can't believe it too ! More noise at lower ISO.
Though I understand Daniel explanations better, what happens should you combine these shots ? Will the end-results be any better ?
BTW the +2EV had Gain Control - High Gain Up, listed on Flickr while the -2EV did not, what is this or what was this ?


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