True (except the rubbish about perspective - wrong frase): > 1) A 50mm focal length is still a normal perspective only with the > sides cut off, because the sensor is smaller than a 35mm negative, and > so the recorded image is simply smaller because of that.
NoOnsence: > 2) A 50mm focal length is now a medium telephoto perspective, with the > same effects, with regard to image compression (from front to back) > and depth of field, in the same way that on a large format camera a > 50mm focal length is a wide perspective. Focal lengths does not change perspective - only changing the camera position does. Different focal lengths dows NOT produce different perspectives. One lens will make the same image no matter what camera it's mounted on. Smaller sensores just show/record a smaller part of it. Different formats crop differently, that's all. DOF doesn't changs either. DOF is dertemined by aperture and focal length. Nothing else. The same lens will produce the same DOF on any format. But if you change the lens in order to obtain a different FOV (perhaps to make up for the crop factor) then the DOF will change as well. Shorter focal lengths have more DOF than longer focal lengths. This has NOTHING, I mean absolutely NOTHING to do with the recording format - AT ALL. Same lens, same perspective, same DOF. Regardless of recording format. It's really that simple. Regards Jens Jens Bladt http://www.jensbladt.dk -----Oprindelig meddelelse----- Fra: mike wilson [mailto:[EMAIL PROTECTED] Sendt: 22. marts 2006 09:33 Til: [email protected] Emne: Re: crop factor vs. telephoto factor > > From: "Russell Kerstetter" <[EMAIL PROTECTED]> > Date: 2006/03/21 Tue PM 09:15:41 GMT > To: [email protected] > Subject: crop factor vs. telephoto factor > > I mostly lurk here, however I do have a question that I have had > answered is two different ways, and always by someone who knows more > than me. > > The Pentax dslr's have a 1.5 crop factor, so this means either: > > 1) A 50mm focal length is still a normal perspective only with the > sides cut off, because the sensor is smaller than a 35mm negative, and > so the recorded image is simply smaller because of that. > > ....or.... > > 2) A 50mm focal length is now a medium telephoto perspective, with the > same effects, with regard to image compression (from front to back) > and depth of field, in the same way that on a large format camera a > 50mm focal length is a wide perspective. > > So.... > > I feel like there is some concept about the mechanics of a lens that I > do not understand, but both explanations make sense to me, so I don't > know. > > Russell I think of it in terms of the output. If you make a same-size print of the view from both systems, the 35mm film print will cover more and will therefore appear to be wider angle. The APS digital print will cover less but, because it is the same size print as the 35mm, has to be enlarged further and looks more telephoto. You get the same effect if you project the images to the same size. The change of image dof compression is minimal compared to the crop/telephoto effect. m ----------------------------------------- Email sent from www.ntlworld.com Virus-checked using McAfee(R) Software Visit www.ntlworld.com/security for more information -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.2.6/287 - Release Date: 03/21/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.3.0/290 - Release Date: 03/23/2006
