Shoot! I got some JCO leakage with this message ;-(( Can't imagine what I've missed. Please don't fill me in ;-))
Shel > [Original Message] > From: Tom C > So? He's arguing a moot point and talking in circles. > > We all *already know* that the mathematically calculated DOF for a given > lens at at a given aperture is constant, regardless of whether the > camera/lens is moved 10 feet forward or 10 feet backwards. The DOF is not > reliant on the position of the camera. Moving the camera/lens will merely > change whether certain elements in the composition fall within or outside of > the DOF. That's not news to me and certainly not news to Mr. Robb. > > Similar is an imprecise term. Therefore saying something is *SIMILAR*, when > it is indeed similar, is a true statement. John is attempting to refute > that. > > His statement that DOF "**changes*** with focal length" is *true*. BUT, > that does not mean, that the DOF of two lenses at like apertures, of close > but different focal lengths, are not similar. The DOF *is* similar, albeit > *different*. > > I'm 5'10" tall. Someone else is 5' 11" tall. It can be said that are > heights are similar, though of course they are not exactly the same. > > Similar: > > 1. having a likeness or resemblance, esp. in a general way: two similar > houses. > > 2. Related in appearance or nature; alike though not identical. > > 3. marked by correspondence or resemblance; "similar food at similar > prices"; "problems similar to mine"; "they wore similar coats" > > 4. having the same or similar characteristics; "all politicians are alike"; > "they looked utterly alike"; "friends are generally alike in background and > taste" > > I don't know why he wants to argue that something is not similar when it is. > Nobody said it was exactly the same. > >From: Paul Stenquist > >J C O is correct. > > J C O wrote:> > Secondly, whether hes making a scientific statement > or dogmatic whatever, or just generalizing, its > still WRONG, because the DOF isnt kept same OR similar > by changing focal lengths if you keep the same camara > postion, it **changes*** with focal length if you > do that. > > > -----Original Message----- > On Behalf Of Tom C > > > Certainly what you state regarding > > > DOF is true. I believe though the > > > writer was not making a dogmatic > > > absolute statement of scientific fact. > > > He was generalizing. > > > > > >> As the camera: subject/background > > >.>ratio wasn't altered, DOF should be > > >> SIMILAR for all four lenses. > > > > > > I'm pretty sure he knows that actual > > >DOF is not changed by altering the > > > subjects distance from the focal plane. > > > That's only moving subjects in to, > > > out of, or within the range referred to as DOF. > > > as DOF. I think he means that the > > > *perceived* DOF will be *similar*, > > > which is true for lenses close to the > > > > > > same focal length used at close to the > > > same aperture. Not the same, > > > but > > > similar. > > > > > > Tom C. > > > > > > > > >> From: >Reply-To: Pentax-Discuss Mail List <[email protected]> > > >> To: "'Pentax-Discuss Mail List'" <[email protected]> > > >> Subject: RE: M85mm f2.0 bokeh > > >> Date: Sat, 28 Apr 2007 10:26:25 -0400 > > >> > > >> No,this assumption is wrong, DOF is > > >> constant only for same fstop and > > >> MAGIFICATION (in camera ). If he > > >> used same camera position and fstop > > >> and only changed lenses, the shorter > > >> lenses will have same perspective > > >> in the shots but with MORE Depth > > >> of field than the longer lenses. > > >> DOF is a function of magnification, > > >> NOT the "subject/background" ratio. > > > > > > Mr. J. > > > > > >>> > > >> -----Original Message----- > > >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > > >> Behalf Of > > > > > >> William Robb > > >> Sent: Saturday, April 28, 2007 9:10 AM > > >> To: Pentax-Discuss Mail List > > >> Subject: Re: M85mm f2.0 bokeh > > >> > > >> > > >> > > >> ----- Original Message ----- > > >> From: "Paul Stenquist" > > >> Subject: Re: M85mm f2.0 bokeh > > >> > > >> > > >>> Of course the 70 gives you more DOF. Thus, a bit crisper. > > >> > > >> I left the camera position static and cropped the 70mm and 77mm > > >> images > > >> to be similar to the 85mm images. > > >> As the camera: subject/background ratio wasn't altered, DOF should be > > >> similar for all four lenses. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
