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. Tom C. >From: Paul Stenquist <[EMAIL PROTECTED]> >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 18:44:41 -0400 > >J C O is correct. >Paul >On Apr 28, 2007, at 11:02 AM, 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. > > > > Mr J > > > > -----Original Message----- > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > > Behalf Of > > Tom C > > Sent: Saturday, April 28, 2007 10:43 AM > > To: [email protected] > > Subject: RE: M85mm f2.0 bokeh > > > > > > 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. 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. > >> > >> William Robb -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
