----- Original Message ----- From: "Izzet" <izzet@vizo.com> To: "List for Photo/Imaging Educators - Professionals - Students" <photoforum@listserver.isc.rit.edu> Sent: Friday, September 06, 2002 11:28 PM Subject: RE: Digital Cameras-Equiv. focal length revisited > Is magnification only because of the smaller viewing angle? Don't we > have to take the resolving capacity of the optical elements and the > design into consideration? > > Leaving DOF aside, when let's say you want to take a portrait shot, does > the camera to the subject distance with a 35 mm. camera and 120 mm. lens > equal D1 and 80 mm. lens? this appears to be getting far more complicated than it all actually is. If we can grasp the concept, then the theory and the subsequent math will be easier to apply Lets step back a moment and take a sheet of paper and pretend it's a piece of film. I've an A4 sheet in front of me, measure the diagonal distance from one corner to the opposite and it measures to be 360mm. The convention dictates this is the 'normal' focal length for this 'negative' and it has an approximate angle of view of around 47 degrees for this format. Imagine a landscape taken with this lens. It will look the same as one taken with a 45mm lens on a 35mm camera (leave DOF out of it for now). Now draw a small 35mm frame in the middle and imagine how much of that same scene is included in this small frame - not much. You will see that nothing has been enlarged, magnified or any way magically transmogrified - it is simply a smaller frame taken with this 360mm lens... If you were to enlarge this small segment you would see a long lens effect, but that's all. No distances have changed, no special magnification has occured - it's all a matter of imagining the format as being a 'clip' from a huge neg, be it 35mm, 66 or 8x10. The lens focal length used will dictate how much of a field of view is incorperated based on this 'clip' does that make some sense? Karl
