Hello Jens, My personal feeling is that the sensor area is larger than we would like to think. Achieving AF within the sensor bounderies (not visible to us) is all the system is going to do. Classic problem is when the sensor area covers something like eyes, nose and ear. One of them will be in focus, but not necessarily the one you want. Stopped down a bit, it may not show up so much, but with narrow DOF, it does. I remember looking at some of my niece's work from a Nikon D1X+AF 80-200/2.8 lens. I was surprised on close examination how many shots were off just a touch from what would have been ideal.
I operate from the concept that I only us AF when it can be more reliable than me. That equates to a very small percentage of the time. Mostly fast moving subjects that are unpredictable in course. In those cases, there is enough slop in my tracking of the subject, to more than compensate for the very minor miss by AF due to the large sensor area. Anyway, those are my thoughts. -- Best regards, Bruce Monday, December 5, 2005, 2:29:04 PM, you wrote: JB> Small? 2104 x 1468 can easily fill you screen! JB> And yoyu're right - it's probably not the lens (although I had great JB> problems getting sharpness at all at F 2.8 - F3.5: JB> It may very well be the AF system. JB> Yes, I use the term when the lens/camera is focusing further away than it JB> should - that is behind the point where the red square in the viewfinder is. JB> ASome times at the top or above the little circle that confirmes focus in JB> the *ist D. JB> In this shot, I focused at the white streamer (stensikkert.dk) - but look JB> how sharp the brick wall looks here JB> http://www.jensbladt.dk/Test/rooms.html JB> Compared to the second and third shot (made with the FA lens). It can't be JB> that the Tokina has a LOT better DOF at F. 2.8, can it? It must be because JB> the focusing is off. Behind the white board. OR this sample og the lens is JB> not good. JB> I find the SMCP FA 2.8/80-200mm ED(IF) quite good, when focused manually. JB> Regards JB> Jens Bladt JB> http://www.jensbladt.dk JB> -----Oprindelig meddelelse----- JB> Fra: graywolf [mailto:[EMAIL PROTECTED] JB> Sendt: 4. december 2005 22:30 JB> Til: [email protected] JB> Emne: Re: A better 70-200mm F. 2.8 JB> The photos are rather too small to tell anything from. However, it is JB> most likely an auto-focus problem, not one with the lenses. JB> Try manual focus. After you have the proper part of the image in what JB> you think is correct focus, go look out the window for 5 minutes or so, JB> then come back and tweek your focus as quickly and exactly as you can. JB> Now you can take your photo. Do that with the other lenses. Get back to JB> us with the results. JB> I would look at every other posibility with focus problems before JB> blaming the lens. JB> And by the way, from a technician's point of view back focus problems JB> means the lens is not focusing the image exactly the flange to film JB> distance from the lens mount. I do not think that is how you were using JB> the term. JB> graywolf JB> http://www.graywolfphoto.com JB> "Idiot Proof" <==> "Expert Proof" JB> ----------------------------------- JB> Jens Bladt wrote: >>I have been trying out three different lenses in the 70-200mm range. >>Sigma EX 2.8/70-200mm APO >>Tokina AT-X Pro 2.8/80-200mm >>SMCP-FA 2.8/80-200mm ED(IF) >> >>All of them seem to suffer from Back Focus. The Sigma not much, though. >>Had I been offered a used Sigma, I probably would have bought it. >> >>I published a small test showing the problem. >>Due to Back Focus (i BELIEVE), my SMCP F-4-5.6/70-210mm is the sharper one >>at F. 5.6. >> >>Please take a look and feel free to comment: >>http://www.flickr.com/photos/bladt/sets/1509814/ >> >>Regards >>Jens >> >> >> >> >> >>
