I just bought a 7D + 50mm 1.8 and I immediately started shooting with it but I've encountered a problem. So, I've read that if I want to create the cinematic effect I always have to set the shutter speed the double of the frames I'm using (eg if I use 30 frames I should set shutter speed at 1/60).
Shane Hurlbut recommends shooting at 1/50 for 30fps to take the sharpness off video.
That's what I did. Since I want to create that beautiful bokeh effect I have the aperture at 1.8 but the thing is,
Filming at 1.8 is really difficult and kind of unnecessary unless you're doing portraits, most directors will film at 2.8 or F/4. Any small movement of you or your subject will throw your focus off completely. However, if you're desperate for light and filiming at night then a 1.8 could be your best friend. It all depends on your ISO and shutter speeds, if you can't get the light you need from lower shutter speeds and higher ISO setting then you need a lens with a low F/stop.
there's just too much light and the image is all white. I'm doing anything wrong or is it like that?
You need to provide more information here, what time of the day were you filming - day or night, where were you fiiming - inside or outside, under what lighting conditions, what ISO were you using, what was your AWB setting.
Just to let you know, with a 1.8 it lets in a lot of light, if you're filming under bright lights or the sun unless you increase the f/stop on your 1.8, you need to bring down your ISO or increase the shutter speed to compensate. Of course ND filters and polarizers work to keep your ISO and shutter speeds and f/stop where you'd like it to be.
Whenever I shoot photography of landscape with a 28mm 2.8 under the glare of the sun, I will usually have an x4 ND filter, increase the f/stop to f8 or f11 with the ISO set around 100.