Why is the FX30 more noisy when shooting at 100/120fps?

[alisterchapman]

I love the FX30, it's a great little camera and it produces a lovely image. But one thing a few have noticed is that if you shoot at 100fps or 120fps it can be a little more noisy than it is at other frame rates. 

 

When shooting 4K/UHD up to 60fps the FX30 downsamples from 6K of pixels to a 4K recording. This oversampling brings a nice noise reduction, the equivalent to almost 1 stop of exposure (around 4-6dB). When you shoot at 100/120fps the camera reads 4K of pixels, there is no downsampling, so the images will be noticeably more noisy. This is just a limitation of how this camera works, my guess is that it doesn't have enough processing power to convert 6K to 4K at 120fps or perhaps the sensor can't be read at 6K at 120fps. The plus side is that the normal 4K recordings downsampled from 6K really are very good indeed and packed full of detail and texture.

 

Plus, if shooting at 120fps and you choose to use the near equivalent of a 180 degree shutter -  1/250th, you will need 5 times more light to get the same exposure compared to 24fps and 1/48 (180 degrees). So to get the same exposure you need to open up the lens by 5 stops or increase the light level by 5 stops. Any less than this and you will be under exposed and that will make your footage look more noisy.

 

When I shoot at 120fps I will often use 1/125  to gain back 1 stop, then expose nice and bright to help eliminate the extra noise.

 

 

 

 

[julienjarry]

@alisterchapman are you saying that it is noisier even when exposed correctly? Or noisier because generally underexposed (which I know you know). Thanks!

[Jesterface84]

Hi Alister. I’ve been following you since the FS5 and Shogun Inferno and love using your amazing Venice lut for slog 2. That’s said, I  am planning on taking back the fx30 today.

Aside from the extra noise when using 120, I still feel that it produces significant noise when shooting indoors with adequate lighting on 4KS-I and ProRes Raw at 24 frames.  

I feel that the FS5 produces a much cleaner and less noisy image than the Fx30 indoors using the same lighting. Only difference is I’m shooting fs5 w/shogun inferno in slog2 and fx30 w/Atomos ninja V+ in slog 3. 

I bought the fx30 to be a direct upgrade from the FS5. Aside from all the bells and whistles that the fx30 brags about with a 6K sensor 16bit  down to 4.7K 12bit, I didn’t expect my image quality to be better on the FS5. 

 

Are you having the same results or are you achieving a better image quality on the fx30 than on the fs5? Thank you for your time.