It doesnt have to be a "mind experiment", all one would have to do is stop down the 20mm lens of any faster speed to F8 and try to focus it. My 1000mm lens is a refractive lens not a mirror BTW.
I dont understand why AF lenses would shift during zoom any more than manual focus ones unless the tolerances are sloppier to keep costs down and its assumed you will refocus on every exposure anyway. That wouldnt be very good if you want to manual focus the AF zoom lenses though. jco -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Toine Sent: Sunday, November 12, 2006 4:19 AM To: Pentax-Discuss Mail List Subject: Re: Using a Super Tak w/ istDS- A challange to the list? I checked all my zooms and the ones I use are all autofocus and probably shift focus during zoom. Autofocus zooms are not the best lenses for manual focus experiments. I don't need or want "fixed focus" zooms on my (D)SLR's. A videocam should have a fixed focus zoomlens. I don't have the zoom gear to check your claims. I must assume you checked your claim and found it to be true for your eyes, pentaprism, focussing screen, testsubject etc. 1000mm/8.0 thats probably a mirror lens. Focusing my 500mm mirror is a real pain. I have never seen a 20mm/8.0. Focussing my 16mm/2.8 Zenitar is easy. My longest is 560mm/6.8. It's a Novoflex fastshot which helps a lot during focussing. Comparing a 1000mm/8.0 against a non existing 20mm/8.0 is mind experiment. Please post some pictures and/or url's. On 11/11/06, J. C. O'Connell <[EMAIL PROTECTED]> wrote: > You are confusing depth of field with accurate focus. > If you dont care about the depth of field and all > you care about is if your subject falls SOMEWHERE > in the depth of field you might have a point, but > most photographer focus on a specific distance > even with high depth of field condtions to control > the foreground and background DOF zones around > the subject. I know I do, especially when wide f-stops/shallow DOF > conditions exist. > > Ever used a 35mm F2 at F2? I have, and you definately > need to focus it. Your longest glass might be your > most difficult to focus but if you have wides at the > same speed they would be even harder. What speed is you longest manual > glass? Mine is a 1000mm/F8 and its easier to focus than a say a 20mm > F8 would be, I can tell you that. > > As for armchair comment, I have been using SLRS > to take photos for over 30 years so your comments > are without merit. I dont just guess about these things, > they are based on both long experience with many > many cameras and lenses of all types and all the optical theory I have > learned over the years. > > Are you saying you dont find zooms eaeier to focus > more accurately at the long end, too? Because if > you are, I cant believe it, as I have never found that > to not be the case with any zoom I have ever used. > > jco > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > Of Toine > Sent: Saturday, November 11, 2006 3:55 AM > To: Pentax-Discuss Mail List > Subject: Re: Using a Super Tak w/ istDS- A challange to the list? > > > I do. In fact I don't need to focus at all using wide lenses. And my > longest manual glass is the most difficult to focus. Are you sure > you're not an arm chair photographer (nothing wrong with that). I > can't remember any pictures. > > On 11/10/06, J. C. O'Connell <[EMAIL PROTECTED]> wrote: > > OK, I challenge the entire list on the matter. > > Does anyone here actually find or believe that > > wider lenses are just as easy to focus as > > 3X longer lenses at the same fstop? I have > > -- > 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 -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
