just curious but how can i calculate the equivalent 35mm focal length based on chip size?
i'm confused as i thought it would be
35 / (1/3") * focal length
but that doesn't work out?
anyone know the correct way to do this?
Barry_Green
04-24-2006, 03:24 AM
It depends on the chip size, and on a few assumptions.
First, 35mm film isn't necessarily 35mm. 35mm refers to the physical width of the film, but you can't ever use that full width because the sprocket holes take up some of that space. So if you're using still film, then the image is 36mm x 24mm (24mm being the width between the sprockets). But if you're using movie film, the frame is 24mm x 18mm (for full-aperture 4:3) or about 22mm x 12mm for academy 1.85:1).
So that's one problem with the idea of using a simple formula. The second is: 1/3" CCDs are never 1/3". 1/3" refers to the TYPE of the CCD, but never to the actual size. They're always much smaller than the stated size type.
Third problem is: not all 1/3" CCDs are the same size. The HD100's CCD is noticeably smaller than the HVX's, and the HVX's may be smaller than the Sony's. So they're not all the same.
If you're going for a comparison to the field of view on a 35mm still camera, the easiest way to do it is to use Panasonic's published figures: they say the 4.2-55 lens corresponds to 32.5-423mm. So the ratio is about 7.74:1. So whatever your HVX lens is set at, multiply that by 7.74 to get an approximation of what size of a still-camera lens would deliver approximately the same field of view.