Archived posting to the Leica Users Group, 2004/02/16
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]If they said Acros 100, then we'd be talking. S. Dimitrov > From: "B. D. Colen" <bdcolen@earthlink.net> > Reply-To: leica-users@mejac.palo-alto.ca.us > Date: Mon, 16 Feb 2004 16:36:44 -0500 > To: <leica-users@mejac.palo-alto.ca.us> > Subject: RE: digital lenses was: Re: [Leica] Digital Bessa RF > > Actually, someone has done such film to mgp approximations and come up > with, among other things, the fact that at between 5-6 mgp you get > results equal to that of 35 mm tri-x. Which is all I care about. ;-) > > -----Original Message----- > From: owner-leica-users@mejac.palo-alto.ca.us > [mailto:owner-leica-users@mejac.palo-alto.ca.us] On Behalf Of Jonathan > Borden > Sent: Monday, February 16, 2004 4:07 PM > To: leica-users@mejac.palo-alto.ca.us > Subject: digital lenses was: Re: [Leica] Digital Bessa RF > > > Feli di Giorgio wrote: > >> On Mon, 2004-02-16 at 03:00, frank.dernie@btinternet.com wrote: >> >> >>> The problem is, Jim, that we do not need film dimension to match film >>> quality, digital sensors about 1/4 the size of Minox film match 35mm >>> P&S quality. We only need a full size sensor to utilise the full >>> angle of view of our existing 35mm design lenses >>> >>> > It is a mistake to assume that an optimal 35 mm lens (e.g. "M" series) > will be optimal for a smaller imaging area. Consider state of the art LF > > lenses e.g. the Schneider Symmar XL 150mm f5.6 which covers 8x10" -- I > don't see people clamoring to use this in 35mm -- indeed it would be a > rather mediocre lens even though its sweet central spot covers > the > 35mm film area. > > The issue is that optimizing a lens for 8x10 is much different than > optimizing a lens for 35mm or a smaller area. > >> Frank >> >> That may be true, but I really detest the increase in DOF you get with >> the 1.5 multiplication factor. >> >> >> > I believe the actual DOF is related to the F stop and focal length -- > you mean the *apparent* increase in DOF. The way to correct for that > would be to use a wider F stop. Indeed for a lens optimized to a smaller > > imaging area you should be able to use a wider maximal F stop. All else > being equal such a lens should also have a *high* resolving power in > lpmm. > > The question has arisen as to how many pixels are needed to approximate > 35mm film. Assume 75 lpmm that would be approximately 2000 lines x > 2000lines or at least 2 pixels/line = 16 megapixels. Now if your lens is > > not good, or your focus is off or your hands shake etc, you need less > pixels -- and also remember that there isn't necessarily a 1:2 > correlation between lines and pixels (for example it is widely > acknowledged that a digital CD recording at 44 khz cannot truly > reproduce an analog recording even though the human ear cannot hear > 20 > > khz) i.e. you probably should have more pixels to capture all the > information. > > In any case this is a back of the napkin approximation that tells us > that a good 5 megapixel sensor is not enough to equal good 35mm film > given a high quality lens. The 75 LPmm is for Provia F 100 slide film -- > > for Tech Pan and on a tripod, you are going to need many more > megapixels. > > Jonathan > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html > > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html