GH2 Crop Factor

[Andrew Rowe]

This will probably be old info for a lot of people, but I thought I'd put it up here for reference, having been unable to find GH2 specific info on the subject using Google...

Having done three projects this month using multiple camera models, one of which in each case was a GH2 (the others being Red Ones, an Aaton XTR (Super16) and Canon DSLRs), I noticed that most of the information I've seen on the web about crop factors is some way off the mark for the GH2 itself - and is obviously untrue if you put the camera next to another and compare field of view by eye. Using a 16mm lens on a Red One at 2K resolution, you get a similar field of view to a 25mm lens on the GH2 for example - whereas I had been expecting the two to have roughly the same crop.

I think this is probably because most of the online comparisons take full frame 35mm stills as their standard, and don't take into account the fact that using the 4:3 specs for the GH2's sensor is irrelevant for 16:9 video. Most cameras crop to 16:9, reducing their field of view, but the GH2 actually uses a wider area of the sensor than in its 4:3 stills mode, so I made some calculations that take this into account. The following is for video only and is worked out using the diagonals of the area of the sensor that is actually in use to produce 16:9 images.

I understand that the GH2 Sensor is effectively 18.7mm x 10.5mm in 16:9 mode (21.4mm diagonal). There are some other figures floating around, but the difference is small and I stuck to info generated from Panasonic's published specs.

Crop factor (approx.) compared to: 5DMk2 (41.3mm diag.) is x1.9
5K Red Epic (31.3mm diag.) is x1.5
Alexa (27.3mm diag.) is x1.3
7D (25.6mm diag.) is x1.2
4K Red One (25.5mm diag.) is x1.2
Non-anamorphic (e.g. 3-perf) 35mm (23.8mm diag.) is x1.1
4K Scarlet (23.8mm diag.) is x1.1
3K Scarlet (17.9mm diag.) is x0.8
Super 16mm (13.8mm diag.) is x0.6
2/3" video (11mm diag.) is x0.5

There may be inaccuracies in my calculations but I reckon they're correct to one decimal place. What this effectively boils down to in the real world is:

i) Double the focal length to find the lens with equivalent FOV on the 5DMk2.
ii) Use a lens of the same focal length for equivalent FOV on a 7D, Red One (4K), Scarlet (4K) or non-anamorphic 35mm.
iii) Halve the focal length to find the lens with equivalent FOV on Super 16, Red One (2K), Scarlet (2K) or 2/3" video.