You're correct on this JCO. Bill Robb is bating you. Ignore him and he'll stop. Paul On Nov 13, 2006, at 10:51 PM, J. C. O'Connell wrote:
> I never said it was always a "problem", I said its > harder to manually the wider you go. Secondly, it > doesn't matter whether its prime or zoom, > the difference is the same because its > DOF related and the DOF is the same for > for primes and zooms at the same focal > lengths. Lastly I use the zoom example > because its the easiest and fastest > way to make the comparison, changing > primes makes for a slow change and the > comparison is harder to make and more > error prone due to the time difference > between the comparisons. Its similar > to audio testing, its better if you > can compare back and forth instantly > rather than relying on memory well after > the first sampling. Its also a good > example because I believe everybody > knows its true. No one has posted otherwise > on the entire list. If there was no > difference between focussing difficulties > of a wide and a tele at the same aperture, > how can you account for the fact that > zooms are easier to focus at the long end? > > jco > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of > William Robb > Sent: Monday, November 13, 2006 10:37 PM > To: Pentax-Discuss Mail List > Subject: Re: RE: RE: Using a Super Tak w/ istDS- A challange to the > list? > > > > ----- Original Message ----- > From: "J. C. O'Connell" > Subject: [Norton AntiSpam] RE: RE: Using a Super Tak w/ istDS- A > challange to the list? > > >> Dear Sir ( is that gentlemanly enough) , >> You forgot to mention fstop used on the >> 105 lens and I don't even think there is >> such a thing as a K105/2.5 lens if I am >> not mistaken. > > Pardon the typos. > You've made a few yourself over time, I'm sure you understand. > > That would be an SMC Pentax 105mm f/2.8 lens at f/8. > >> >> Secondly, have YOU ever used a constant >> aperture zoom of ANY range that wasn't easier >> to focus manually on the longer end than on the shorter >> end? I haven't and this pretty much squelches >> any argument to the contrary over this. Its just >> simple differences in the DOF. The more DOF >> you have, the harder it is to find the true >> focal point because the DOF is masking it >> to some extent and you don't pop in an out >> of focus as quickly as you do with a longer >> lens which has shallower DOF at the same >> fstop and distance. > > I don't have much use for zooms, the only constant aperture one I > own is > > a 70-210 f/2.8. > Shel originally mentioned that he didn't see much difference in > ease of > focus between a couple of primes anyway, so why bring zooms into the > discussion? > There was a comment made that he (and I) didn't have more trouble > focusing a medium wide angle lens than a short telephoto when stopped > down to f/8, using an istDs (shel) and an istD (me). > I am aware of the optical theory you are using for your assertion, I > suspect that the difference in DOF between the two focal lengths isn't > great enough to cause either Shel or myself a problem. > I don't care if you disagree with what my eyes tell me or not, since > what my eyes tell me is true. > > William Robb > > > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
