L39 extended camera zoom very low FPS

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when i zoom the plane close my fps reduces to 20-17 from 50 60 other planes dont have this problem only l39 has cockpit fps is just fine only f2 camera zoom buggy

 

r7 260x 2 gb

i3 540

4 gb ram

 

i dont think this problem is about my system why only l39 has this problem then ? why a10c is not or f15 hasnt this problem ?

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problem is about skin [russian air force] i changed skin problem is disappeared this can be close