I agree with John on this. It is very obvious that unless you have lenses with infinite resolution (and you dont), that capturing ALL of the image from a 50mm lens is going to be sharper than capturing a center crop from a 33mm lens. ( 1.5 crop factor sensor) This is assuming both the 50mm and the 33mm have the same lpmm and it is not infinite.
JCO ---------------------------------------------------------------------------- J.C. O'Connell mailto:[EMAIL PROTECTED] http://jcoconnell.com ---------------------------------------------------------------------------- -----Original Message----- From: John Forbes [mailto:[EMAIL PROTECTED] Sent: Tuesday, March 09, 2004 4:08 PM To: [EMAIL PROTECTED] Subject: Re: *ist D sensor and 35mm lens resolution Surely this is quite simple. With the *ist D you are getting a crop of the normal image that you would get with a 35mm film camera. Therefore, to view the image at the same size, you have to blow it up more, and thereby lose effective resolution. John On Tue, 09 Mar 2004 14:40:13 -0500, graywolf <[EMAIL PROTECTED]> wrote: > There are two opposing things that control lens resolution. There are > laws of physics involved that give a maximum theoretical capability that > any lens can have. > > Basically those two things are diffraction, and aberrations. They are > opposing because closing a lens down increases diffraction, and openning > it up increases aberrations. A lens is said to be diffraction limited > when all the aberrations are corrected at the widest apperture. That is > fairly easy to do with something like the old Kodak Ektar 200mm/f7.7 > (covers 4x5, well actually 5x7 but it is not diffraction limited on 5x7) > because the maximum aperture is only about f8. The French made Kinoptik > 100mm/f2.0 (covers 35mm)which is also supposed to be diffraction limited > is a very expensive lens as it is much harder to do with a fast lens. It > is also harder to do with wider fields of view which is why the Ektar is > not diffraction limited on 5x7. > > The wider the aperture the higher the resolution, as long as the > aberrations are fully corrected. The Kinoptik with its 50mm aperture has > an aerial resolution of about 400 lines per millimeter, the Ektar with > 1/2 that has about 200 lpm. > > Now it is easier to make a fully corrected large aperture lens at > shorter focal lengths, so that is why they claim shorter lenses have > higher resolution. But that unless you are willing to pay astronomical > amounts for diffraction limited lenses is only theoretically, especially > today when they can make large lenses to the same tolerances as smaller > ones. > > Note: Those high resolution numbers I mentioned are for aerial images, > examined with a microscope (also they are an approximation as I am too > lazy to look up or calculate the actual figures). Overall resolution on > film or sensor will alway be lower than the lowest resolution in the > system which is usually the film or sensor resolution. As an example, > with that Kinoptik (400 lpm), on Tech Pan (200 lpm) you would get > something like 150 lpm overall, which is about the best your are going > to do with what I know is available out there. > > Also note that by the time you make your print that near impossible 150 > lpm on 35mm is only equal to an easy to get 37.5 lpm on 4x5 which should > put the whole thing into perspective. > > -- Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/
