Another way of saying the same thing. If a portion of your image takes up 16mm from top to bottom on an APS size sensor, it will fill the frame. On a 24.mm sensor, that same portion of your image will still take up 16mm in height, but there will be 8mm of space above or below that same portion of your image. So while a 200mm lens is a 200mm lens, regardless of format, it will take up an area on an APS sized sensor that would it would take a 300mm lens to cover on a 35mm sensor. Does this make sense?
It would take a ~33mm lens to give the same coverage on an APS size sensor/film that a 50mm lens covers on a 35mm size sensor/film. Bill ----- Original Message ----- From: "graywolf" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, September 30, 2003 2:42 PM Subject: Re: "normal" focal length of *ist-D? > You are getting there, Marie. Take your 24x36mm negative and trim it > down to 16x24mm. That is what is happening. There is no actual change in > focal length. It is just a crop. > > The reason they started using the 35mm equivalent on P&S digitals is > because they all tend to have different size sensors and odd-ball focal > length lenses. It was just a convinence to make it easier to compair one > camera to another. Somehow folks start thinking it was more than that, > and all of a sudden there are lots of experts pondificating about it. > Many of the things everyone KNOWS about photography came about the same > way. > > So no, your 200mm lens does not magically become a 300mm lens. It is > just a 200mm lens with a smaller negative. > > > [EMAIL PROTECTED] wrote: > > Okay, let me see if I have got this. A 50mm on a *istD is still going to look > > through the viewfinder like a 50mm -- because only the sensor, "film plane", > > has changed not the viewfinder. But it will actually be a 75mm as far as the > > sensor goes, as far as the field of view or whatever it is called, goes. So to > > "emulate" a 50mm on a *ist D one really wants a 35mm or a 40mm. > > > > Well, this "magnification" thing (cropping the center of the lens) sounded > > great: increased "focal length" for big glass (ergo making it easier to get big > > glass cheaper), and cropping the center means less distortion or vignetting > > on not perfect lenses, etc. > > > > But I am not so sure that I like the idea that you cannot see the increase > > through the viewfinder. I rely heavy on what I can see through the viewfinder. > > Using mainly zooms, that is what I use to determine if I want to shoot at 70mm > > or 135mm or something. > > > > So maybe there are drawbacks in not having a full sensor, after all. > > > > Am I following all this correctly? Or basically so? ;-) > > > > Marnie aka Doe > > > > > > -- > graywolf > http://graywolfphoto.com > > >
