7D is 1.6 crop factor, so a 50mm will behave like a 80mm lens, the "mechanics" of the optics of the lens doesn't change but the resulting picture does, and that's what matters.
On Tue, May 29, 2012 at 5:55 PM, chris <[email protected]> wrote: > On 5/29/12 at 10:28 PM, (Howard Jones) wrote: > >> 1. If you can't get a 100mm lens that is designed for >> >> a crop film back, ie compensates for the sensor size, then >> you are correct that in this case the focal length is the >> same, regardless of sensor size, however the fov is >> different. >> >> However if you can buy a lens that has compensated for the >> sensor size and gives the same fov as a 35mm lens then >> there is a discrepancy. >> I'm under the (mis)understanding that the latter is available, >> however I can quite believe I'm mistaken. >> > > well, there might be a case that somebody labels the lens with a "35mm > full frame equivalent" (rather common with point-and shoot cameras, which > say something like 4-40mm, 35-350mm equivalent)... but that would be not > the proper focal length optically speaking, and they should still list the > real focal length. (I've never seen anything like this for cameras with > interchangable lenses though) > > but to clear things up, let's take the simple example of a canon 5D vs 7D > (full 135mm frame size vs APS size): > > if you buy a 50mm built for the 5D, it will give you a field of view of a > "normal lens" and cover the full sensor size. > > if you put the same 50mm on the 7D, it is still a 50mm for all optical > calculations, and it will give you the field of view of a 50mm on a 7D - > which in comparison looks about the same as if you would put a 75mm lens on > the 5D (hence people who were used to the 5D call it a 1.5 crop factor - > but it's really just old habits - we could just as well call it 0.6x crop > factor if you were used to a 6x6 hasseblad camera where you'd consider 80mm > normal). it's still a 50mm lens though. > > if you buy a 50mm designed for the 7D, again it will give you the same > field of view as the other 50mm, and again it will look like a slight > telephoto lens. so if you use the 5D 50mm, or the 7D 50mm doesn't make any > difference (for the field of view). > > lastly if you put the 50mm designed for the 7D on the 5D, it will still > behave optically like a standard 50mm - ie it gives you the same > magnification per sensor area. however it wont likely wont cover the full > sensor size with light, meaning you can't really use it for the full frame. > so you would have to crop an APS size piece out of the image if you don't > want the vignetting. one could argue that this cropping makes it an > narrower field of view, ie slight telephoto lens, but this it's rather > because you're not using the full sensor size and not a change in the > optical properties of the lens. > > but even if you buy a 50mm lens for a 6x6cm hasselblad it will give you > the same field of view (and magnification) as the 5D 50mm and the 7D 50mm. > so a 50mm is a 50mm is a 50mm ;) > > > 2. We are all assuming nuke behaves correctly in this >> fashion. In the back of my mind, if you put the focal >> length into the camera tracker and then change the film >> back, it changes the focal length, but you can then change >> it back. >> > as far as i can see it doesn't. it changes field of view (as is expected). > and even if it did it would be rather due to decisions in UI behavior > rather then to the physics behind it. > > hope that clears up a few things > ++ chris > > > > ______________________________**_________________ > Nuke-users mailing list > [email protected].**co.uk<[email protected]>, > http://forums.thefoundry.co.**uk/ <http://forums.thefoundry.co.uk/> > http://support.thefoundry.co.**uk/cgi-bin/mailman/listinfo/**nuke-users<http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users> >
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