The point remains that the difference in perceived sharpness of the background with the 70mm lens is due to the difference in focal length. End of story. The trolling should stop. Paul On Apr 28, 2007, at 9:40 PM, Shel Belinkoff wrote:
> 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 <pdml@pdml.net> >>>>> To: "'Pentax-Discuss Mail List'" <pdml@pdml.net> >>>>> 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 > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
