I don’t think that anyone has mentioned this yet – lens perspective. This is a long post, but well worth reading as the issue never seems to get mentioned.
Firstly, I agree with everything said above. The sensor size of the GH4 (and the similarly sized 16mm film cameras) can produce beautiful looking movies – especially with expensive lenses. However, creating the full-frame equivalent field of view and depth of field by using wider and faster lenses, will not give exactly the same result as shooting with a 35mm sensor.
The reason for this is to do with the “perspective” changes inherent with using wider lenses. Imagine taking a photograph with a 35mm-sensor camera like a Canon 5D, fixed on a tripod with a 50mm lens pointing at a beautiful landscape. Then, without moving the camera, swap the lens for a 25mm. The field of view is now much wider, but we can still achieve the same view by cropping, as if the camera sensor were the size of the GH4 sensor. However, compared to the 50mm lens, the wider angle of the 25mm lens means that objects in the foreground look larger than those in the background – and that perspective distortion is still present in the centre-cropped image.
If you take this example to extremes. On a full-frame camera a 16mm lens is very wide and the distortion is obvious. However, if you stick an 8mm lens on the same camera, then the world turns completely fish-eyed. Even if you do a 2x crop like a GH4 sensor would, the remaining image will still look more distorted than the photograph taken with the 16mm lens on the full-frame camera – even though the field of view is the same.
As a rule of thumb, the longer the lens the more pleasing the image. The longer lens makes objects in the foreground appear to be part of the same world as the background. It has a flattening effect on our three dimensional world which is pleasing to the eye. This is well known in the world of photography, where medium and large format film cameras produce stunning, hypnotic images which cannot be equalled by 35mm cameras. This is because they use much longer lenses to achieve the desired field of view.
Movies shot on 70mm film have a similar quality. Even if they are printed onto 35mm film for projection purposes, the original “perspective” of the longer lenses which shot the movie still remains in the image. Arri has produced the Alexa-65 with a 65mm sensor. It’s a 6k camera, but that’s only 20-million pixels which could easily fit onto a 35mm-sensor. The reason for the big sensor is to allow DP’s the use of the long lenses that they love. This “perspective” phenomenon is also the reason that even the highest quality video cameras do not create a filmic look – because their tiny sensors need wide lenses.
The good news is that the more towards the centre of the image you look, the less pronounced the “perspective” qualities of the lens are. The GH4 may need doubly as wide lenses as a full-frame camera, but it only looks at the centre 50% of the full frame – so the “perspective” issue is minimised – but it is still there.
So, in summary - don’t worry too much about it because the GH4 has a pretty big sensor and, as mentioned by many people above, there is more to the look of a movie than this one issue. But if you want the really real filmic look, then you’ve got to go full-frame 35mm or larger.