However I also had (and still have) a laptop with SLI 8800GTX, on which the game fan fine fps-wise but there was this unbearable sky flickering whenever I turned my character's view left/right or up/down or forward/back.
It looks exactly like this:
http://www.youtube.com/watch?v=QZDbZQZcEo0
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I had posted about this issue in these forums some 3 years ago, there were many other players using AMD Crossfire or Nvidia SLI who reported the same problem. However, no fix was found then.
The only 'work-around' was to either:
1) Remove one card (and get low fps); or
2) Disable SLI/Crossfire from the AMD or Nvidia Control Panel (not always possible, sometimes the option just isn't there in the case of AMD) and get low fps; or
3) Disable HDR and play an unrealistic and un-immersive game losing all of the lighting effects.
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So I gave up playing FO3 on the laptop, continuing the game only on my desktop pc with the single 8800GT instead.
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Some months later I upgraded my desktop pc graphics to an AMD HD5970.
Playing FO3 on my upgraded desktop gave me exactly the same problem that I had on the laptop (the HD5970 is a 'single' card with 2 GPU's, essentially crossfire in one card).
So I forgot about FO3 and played New Vegas........
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Incidentally I have to mention that I never got this problem in Fallout New Vegas, or TESIV Oblivion, and not even now in TESV Skyrim.
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Some days ago (after getting bored playing Skyrim for 4 months!) I decided to go back to Fallout 3.... and dang-it... I had totally forgotten about this problem... only to get my memory jolted back when I saw it was still there!
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I googled the issue... unless I'm missing something it still hasn't been solved?
But is it possible? This game's been released nearly 4 years ago...
I'm pretty sure it's not a driver issue. Whether the graphics cards are Nvidia or AMD the problem persists. And that's after 4 years of driver releases...
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Please help. This is so sad