Its pretty simple. The focal length of a lens is determined by the system it is designed for. (large format lenses being the most optically pure in design) So once we know the depth of the box we are going to attached the Lens to and the desired FOV (to limit the image circle needed and the amount of glass required to make it) We then find the point at which the lens design will be in focus at Infinity. This places the rear nodal point (the last place the light will cross itself. On a simple lens there is only one nodal point) a given distance (its closest) from the imaging plain. That distance is the focal length of the lens.
Randy S. Little http://www.rslittle.com On Tue, May 29, 2012 at 2:51 PM, chris <[email protected]> wrote: > On 5/29/12 at 10:55 PM, (chris) wrote: >> >> 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 > > > small mistake in numbers here, compared to a 6x6, the 7D would have a crop > factor of around 2.5x. but the point was that whenever you use the crop > factor term, you'd have to define *what* it's compared to to make sense. so > while it might make it easier for people who only used one format before > (like, photographers going from 135mm film to APS sized sensor digital > cameras), it's very confusing for all those who use multiple formats (16mm? > super16mm? 35 academy? alexa? cinemascope? etc). so it's best to just state > the *true* (ie optical correct) focal length and the sensor/film size that > you used to record the image. > > sorry for drifting off-topic... as nathan said, the short story is just use > the correct focal length and the correct film back ;) > > ++ chris > > _______________________________________________ > Nuke-users mailing list > [email protected], http://forums.thefoundry.co.uk/ > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users _______________________________________________ Nuke-users mailing list [email protected], http://forums.thefoundry.co.uk/ http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users
