Re: simple-as-dirt focus calibration method
On Apr 7, 2012, at 23:19, Miserere wrote: Well Charles, now that Phase Detect focusing agrees with Contrast Detect focusing, and assuming CD focusing is correct, you now have the enviable task of making sure manual focusing agrees too! If an autofocused image doesn't look focused through the viewfinder, you'll have to install some shims or file your focusing screen, depending on whether the viewfinder front- or back-focuses. Best of luck with that! :-) Fun times! I'll get right on that, for sure... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On 8 April 2012 11:34, Charles Robinson charl...@visi.com wrote: On Apr 7, 2012, at 23:19, Miserere wrote: Well Charles, now that Phase Detect focusing agrees with Contrast Detect focusing, and assuming CD focusing is correct, you now have the enviable task of making sure manual focusing agrees too! If an autofocused image doesn't look focused through the viewfinder, you'll have to install some shims or file your focusing screen, depending on whether the viewfinder front- or back-focuses. Best of luck with that! :-) Fun times! I'll get right on that, for sure... -Charles Fun indeed! :-) I need to correct my statement above: If when you manual focus, your images are back-focused, then you need to install shims. If they are front-focused, you need to file the focusing screen. Shims are a lot easier than filing! Oh, and both shims and filing take place on the upper part of the focusing screen (i.e., the part facing the pentaprism). Cheers, —M. \/\/o/\/\ -- http://WorldOfMiserere.com http://EnticingTheLight.com A Quest for Photographic Enlightenment -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
Well Charles, now that Phase Detect focusing agrees with Contrast Detect focusing, and assuming CD focusing is correct, you now have the enviable task of making sure manual focusing agrees too! If an autofocused image doesn't look focused through the viewfinder, you'll have to install some shims or file your focusing screen, depending on whether the viewfinder front- or back-focuses. Best of luck with that! :-) —M. \/\/o/\/\ -- http://WorldOfMiserere.com http://EnticingTheLight.com A Quest for Photographic Enlightenment On 4 April 2012 10:37, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
A chore I have put off for a while, too. And I think my FA-50 1.4 could use a little calibrating... I would love for it to be this simple... I await the bubble-poppers... :) -c On Wed, Apr 4, 2012 at 10:37 AM, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
I think that should work (and does indeed sound like a simpler way to go about it), but I'd still want to use a flat surface for the target. There's no guarantee that the AF sensor is locking on exactly the same part of the scene as the live view AF, so a wine bottle (with a curved surface) might not be the best choice. On Wed, Apr 4, 2012 at 10:55 AM, Christine Nielsen ch...@inielsen.net wrote: A chore I have put off for a while, too. And I think my FA-50 1.4 could use a little calibrating... I would love for it to be this simple... I await the bubble-poppers... :) -c On Wed, Apr 4, 2012 at 10:37 AM, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
Yeah..me too. Probably readying their needles as I (two finger) type. ;-) Jack - Original Message - From: Christine Nielsen ch...@inielsen.net To: Pentax-Discuss Mail List pdml@pdml.net Cc: Sent: Wednesday, April 4, 2012 7:55 AM Subject: Re: simple-as-dirt focus calibration method A chore I have put off for a while, too. And I think my FA-50 1.4 could use a little calibrating... I would love for it to be this simple... I await the bubble-poppers... :) -c On Wed, Apr 4, 2012 at 10:37 AM, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
Wouldn't the results be affected by the # of AF sensors in use? What does your AF Select AF Point say? I wonder how an AF lens can be in error if the sensor is aligned with the ground glass and film/sensor plane. What am I missing? Sincerely, Collin Brendemuehl He is no fool who gives what he cannot keep to gain what he cannot lose -- Jim Elliott -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Apr 4, 2012, at 10:35, Collin Brendemuehl wrote: Wouldn't the results be affected by the # of AF sensors in use? What does your AF Select AF Point say? From my list of instructions: 2. Set up camera on tripod with center focus point selected. I wonder how an AF lens can be in error if the sensor is aligned with the ground glass and film/sensor plane. What am I missing? I don't know how all of the mumbo-jumbo happens in the background... but I do know that some of my lenses needed calibration and some didn't! -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
That sounds super easy! I will give that a shot today. My FA50 1.4 has always had a horrible back-focus issue on just about all my dSLRs, so it'll be great to finally have that sorted. Thanks for sharing! John -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Apr 4, 2012, at 12:00, John Celio wrote: That sounds super easy! I will give that a shot today. My FA50 1.4 has always had a horrible back-focus issue on just about all my dSLRs, so it'll be great to finally have that sorted. Thanks for sharing! I'm sure we'll all appreciate a follow-up, John! -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
This moire method works wonderfully--much better than a wine bottle (drinking the wine is nice, though): http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html Rick http://photo.net/photos/RickW - Original Message - From: Bryan Jacoby bryan.jac...@gmail.com To: Pentax-Discuss Mail List pdml@pdml.net Cc: Sent: Wednesday, April 4, 2012 11:12 AM Subject: Re: simple-as-dirt focus calibration method I think that should work (and does indeed sound like a simpler way to go about it), but I'd still want to use a flat surface for the target. There's no guarantee that the AF sensor is locking on exactly the same part of the scene as the live view AF, so a wine bottle (with a curved surface) might not be the best choice. On Wed, Apr 4, 2012 at 10:55 AM, Christine Nielsen ch...@inielsen.net wrote: A chore I have put off for a while, too. And I think my FA-50 1.4 could use a little calibrating... I would love for it to be this simple... I await the bubble-poppers... :) -c On Wed, Apr 4, 2012 at 10:37 AM, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
I'm not sure what is being accomplished here. How do you know which of the two focusing methods techniques is errant? Is autofocus through the live view system more accurate than autofocus through the lens? It sounds like they are testing for differences in the two focusing systems. The lens is the only constant in the procedure. With the little I know about the focusing system, it seems that the only thing this proves is that the two focusing methods result in either identical or different results. I'm not trying to be argumentative here, I'm just trying to understand. gs George Sinos gsi...@gmail.com www.georgesphotos.net plus.georgesinos.com On Wed, Apr 4, 2012 at 10:17 AM, Jack Davis jdavi...@yahoo.com wrote: Yeah..me too. Probably readying their needles as I (two finger) type. ;-) Jack - Original Message - From: Christine Nielsen ch...@inielsen.net To: Pentax-Discuss Mail List pdml@pdml.net Cc: Sent: Wednesday, April 4, 2012 7:55 AM Subject: Re: simple-as-dirt focus calibration method A chore I have put off for a while, too. And I think my FA-50 1.4 could use a little calibrating... I would love for it to be this simple... I await the bubble-poppers... :) -c On Wed, Apr 4, 2012 at 10:37 AM, Charles Robinson charl...@visi.com wrote: I don't know why I never thought of doing it this way... My FA-50 1.7 has always given me surprisingly soft results and I've always suspected that the focus needed to be calibrated but never had the time. In the kind of low-light situations where I use it, manual focus is as dodgy as auto. Yesterday I found a website which described a dead-simple way to do it if you have LiveView (and the K7 has exactly that). No focus targets or brick walls needed. Here's how it works: 1. Set up a target a few feet away. I used a wine bottle. 2. Set up camera on tripod with center focus point selected. 3. In Live View, press AF and wait for focus to be locked. 4. Turn off Live View 5. Press the AF button again and watch which way the focus ring moves. Ideally it shouldn't move at all! 6. If it does move... go into the focus calibration settings in the custom menu and add/remove points. 7. Repeat steps 3-6 until the damned ring holds still. Done. My FA-50 needed seven correction steps to the left (can't remember if that's plus or minus) - SERIOUSLY out of whack. My DA-35 only needed 2 steps in the other direction. My Tamron 28-200 was dead on as is my 16-50. I can't wait to use the FA-50 in another low-light situation to see if it nails the focus in a real-world situation now. It never has before. :-( It was so simple and easy to do I almost wished I had more AF lenses to try it on! If anyone would like to pop my bubble, please go ahead and tell me why this isn't the right way to go about it... -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Wed, Apr 4, 2012 at 2:01 PM, George Sinos gsi...@gmail.com wrote: I'm not sure what is being accomplished here. How do you know which of the two focusing methods techniques is errant? Live View is correct, by definition. It's based directly on the imaging sensor. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
OK, I just looked it up. If I understand it correctly, the default focusing mode for live view is based on contrast as detected by the imaging sensor. Focusing through the optical system uses a separate phase detection sensor. I guess the method assumes that the live view, contrast-based autofocus system is correct. So an adjustment must be made to the phase-based system to correct any focusing errors in the phase-based system. Evidently, the micro-focus adjustments must not effect the live view, contrast-based focusing system. Otherwise, once you made a microfocus correction, it would seem to me that it would throw off the, previously correct, live-view focusing system. So does that lead to the conclusion that all of this back-focusing business is really a problem with the autofocus system? Otherwise, if the lens was not focusing properly, it should be equally bad through both focusing systems. If that's true people should be saying this camera body back-focuses with this lens instead of the more commonly phrased this lens has a back-focus problem. On the other hand, a guy with two watches never knows the correct time. gs George Sinos gsi...@gmail.com www.georgesphotos.net plus.georgesinos.com On Wed, Apr 4, 2012 at 1:06 PM, Matthew Hunt m...@pobox.com wrote: On Wed, Apr 4, 2012 at 2:01 PM, George Sinos gsi...@gmail.com wrote: I'm not sure what is being accomplished here. How do you know which of the two focusing methods techniques is errant? Live View is correct, by definition. It's based directly on the imaging sensor. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Wed, Apr 4, 2012 at 2:32 PM, George Sinos gsi...@gmail.com wrote: If that's true people should be saying this camera body back-focuses with this lens instead of the more commonly phrased this lens has a back-focus problem. I can't say I understand exactly why this is, but phase detection AF errors can apparently be caused by the body or the lens. I understand why a lens with spherical aberration could front/back focus when used at an aperture setting that's not the same as what the AF sensor is using (often f/5.6); I'm not sure if this would be significant. But there seems to be more to it than that: different copies of the same lens apparently will focus differently on the same body (see http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths). Aside from the optics, at least in some systems, maybe all, AF lenses tell the camera body what the focus distance setting is. This, combined with the how far out of focus is it information from the AF sensor, lets the camera body calculate how much to adjust the focus. I would think that errors in this focus distance encoding would lead to multiple iterations before locking on focus, but not errors in the final locked focus point. Can anybody explain the origin of lens-related phase detection AF errors? -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
OK, I found my answer, and some animated examples here. http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html The short story is that phase-detection measures the error and tells the lens which direction and how far to move to get into the correct position. It's faster, but depends on everything being calibrated. Sort of like saying go three feet to the east and you'll be there. If you both have accurate rulers and compasses it will work fine. The contrast detection method used with live view is iterative and keeps sending correction messages until the image is focused. Slower, but more accurate. So it boils down to the fact that lens and body manufacturing tolerances are wide enough that, for phase-detect focus to be spot-on, each lens-body pair needs to be micro-calibrated. If you can live with the slower contrast-detection focusing of live view, it will probably be more accurate. Anyway, that sheds light on the old my copy of this lens isn't focusing statement. It's more like this copy of the lens on this copy of the body aren't a good match. Bottom line, now I think I understand why the simple calibration method can work. gs George Sinos gsi...@gmail.com www.georgesphotos.net plus.georgesinos.com On Wed, Apr 4, 2012 at 1:56 PM, Bryan Jacoby bryan.jac...@gmail.com wrote: On Wed, Apr 4, 2012 at 2:32 PM, George Sinos gsi...@gmail.com wrote: If that's true people should be saying this camera body back-focuses with this lens instead of the more commonly phrased this lens has a back-focus problem. I can't say I understand exactly why this is, but phase detection AF errors can apparently be caused by the body or the lens. I understand why a lens with spherical aberration could front/back focus when used at an aperture setting that's not the same as what the AF sensor is using (often f/5.6); I'm not sure if this would be significant. But there seems to be more to it than that: different copies of the same lens apparently will focus differently on the same body (see http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths). Aside from the optics, at least in some systems, maybe all, AF lenses tell the camera body what the focus distance setting is. This, combined with the how far out of focus is it information from the AF sensor, lets the camera body calculate how much to adjust the focus. I would think that errors in this focus distance encoding would lead to multiple iterations before locking on focus, but not errors in the final locked focus point. Can anybody explain the origin of lens-related phase detection AF errors? -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
That applet is a great explanation of how phase detection AF works, but I don't think it explains lens-to-lens variation in AF. On Wed, Apr 4, 2012 at 3:27 PM, George Sinos gsi...@gmail.com wrote: OK, I found my answer, and some animated examples here. http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html The short story is that phase-detection measures the error and tells the lens which direction and how far to move to get into the correct position. It's faster, but depends on everything being calibrated. Sort of like saying go three feet to the east and you'll be there. If you both have accurate rulers and compasses it will work fine. The contrast detection method used with live view is iterative and keeps sending correction messages until the image is focused. Slower, but more accurate. So it boils down to the fact that lens and body manufacturing tolerances are wide enough that, for phase-detect focus to be spot-on, each lens-body pair needs to be micro-calibrated. If you can live with the slower contrast-detection focusing of live view, it will probably be more accurate. Anyway, that sheds light on the old my copy of this lens isn't focusing statement. It's more like this copy of the lens on this copy of the body aren't a good match. Bottom line, now I think I understand why the simple calibration method can work. gs George Sinos gsi...@gmail.com www.georgesphotos.net plus.georgesinos.com On Wed, Apr 4, 2012 at 1:56 PM, Bryan Jacoby bryan.jac...@gmail.com wrote: On Wed, Apr 4, 2012 at 2:32 PM, George Sinos gsi...@gmail.com wrote: If that's true people should be saying this camera body back-focuses with this lens instead of the more commonly phrased this lens has a back-focus problem. I can't say I understand exactly why this is, but phase detection AF errors can apparently be caused by the body or the lens. I understand why a lens with spherical aberration could front/back focus when used at an aperture setting that's not the same as what the AF sensor is using (often f/5.6); I'm not sure if this would be significant. But there seems to be more to it than that: different copies of the same lens apparently will focus differently on the same body (see http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths). Aside from the optics, at least in some systems, maybe all, AF lenses tell the camera body what the focus distance setting is. This, combined with the how far out of focus is it information from the AF sensor, lets the camera body calculate how much to adjust the focus. I would think that errors in this focus distance encoding would lead to multiple iterations before locking on focus, but not errors in the final locked focus point. Can anybody explain the origin of lens-related phase detection AF errors? -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Apr 4, 2012, at 14:27, George Sinos wrote:
OK, I found my answer, and some animated examples here.
http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html
Cl. Thanks!
The short story is that phase-detection measures the error and tells
the lens which direction and how far to move to get into the correct
position. It's faster, but depends on everything being calibrated.
Sort of like saying go three feet to the east and you'll be there.
If you both have accurate rulers and compasses it will work fine.
The contrast detection method used with live view is iterative and
keeps sending correction messages until the image is focused. Slower,
but more accurate.
I've noticed the differences when watching the focus dials. In Live-View
(contrast-detect) mode the camera swings wide and then bumps back and forth
over the line in smaller and smaller iterations until it stops at the focus
point.
In phase-detect ('standard') mode, you hit the AF button and it pretty much
just jumps to the final spot. There is a little very-quick fine-tuning once
it's there, but nothing like the wide swings you see when it's focusing in
live-view.
-Charles
--
Charles Robinson - charl...@visi.com
Minneapolis, MN
http://charles.robinsontwins.org
http://www.facebook.com/charles.robinson
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Re: simple-as-dirt focus calibration method
On 4/4/2012 2:06 PM, Matthew Hunt wrote: On Wed, Apr 4, 2012 at 2:01 PM, George Sinosgsi...@gmail.com wrote: I'm not sure what is being accomplished here. How do you know which of the two focusing methods techniques is errant? Live View is correct, by definition. It's based directly on the imaging sensor. Err, no not necessarily, it could suffer from a number of errors, it is however not dependent on the positioning of three separate systems being correct. -- Don't lose heart! They might want to cut it out, and they'll want to avoid a lengthily search. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
You spoke my thoughts exactly, George. Jack From: George Sinos gsi...@gmail.com To: Pentax-Discuss Mail List pdml@pdml.net Sent: Wednesday, April 4, 2012 11:32 AM Subject: Re: simple-as-dirt focus calibration method OK, I just looked it up. If I understand it correctly, the default focusing mode for live view is based on contrast as detected by the imaging sensor. Focusing through the optical system uses a separate phase detection sensor. I guess the method assumes that the live view, contrast-based autofocus system is correct. So an adjustment must be made to the phase-based system to correct any focusing errors in the phase-based system. Evidently, the micro-focus adjustments must not effect the live view, contrast-based focusing system. Otherwise, once you made a microfocus correction, it would seem to me that it would throw off the, previously correct, live-view focusing system. So does that lead to the conclusion that all of this back-focusing business is really a problem with the autofocus system? Otherwise, if the lens was not focusing properly, it should be equally bad through both focusing systems. If that's true people should be saying this camera body back-focuses with this lens instead of the more commonly phrased this lens has a back-focus problem. On the other hand, a guy with two watches never knows the correct time. gs George Sinos gsi...@gmail.com www.georgesphotos.net plus.georgesinos.com On Wed, Apr 4, 2012 at 1:06 PM, Matthew Hunt m...@pobox.com wrote: On Wed, Apr 4, 2012 at 2:01 PM, George Sinos gsi...@gmail.com wrote: I'm not sure what is being accomplished here. How do you know which of the two focusing methods techniques is errant? Live View is correct, by definition. It's based directly on the imaging sensor. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
but I do know that some of my lenses needed calibration and some didn't! The proof of all this obviously will be in the images. Kenneth Waller http://www.pentaxphotogallery.com/kennethwaller - Original Message - From: Charles Robinson charl...@visi.com Subject: Re: simple-as-dirt focus calibration method On Apr 4, 2012, at 10:35, Collin Brendemuehl wrote: Wouldn't the results be affected by the # of AF sensors in use? What does your AF Select AF Point say? From my list of instructions: 2. Set up camera on tripod with center focus point selected. I wonder how an AF lens can be in error if the sensor is aligned with the ground glass and film/sensor plane. What am I missing? I don't know how all of the mumbo-jumbo happens in the background... but I do know that some of my lenses needed calibration and some didn't! -Charles -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On Apr 4, 2012, at 15:18, kwal...@peoplepc.com kwal...@peoplepc.com wrote: but I do know that some of my lenses needed calibration and some didn't! The proof of all this obviously will be in the images. I agree! I was in a hurry to make an appointment last night and couldn't really run any testing beyond shoot and zoom in with the preview image. I'm excited to see if I've breathed new life into my ignore this for critical work lens! -Charles -- Charles Robinson - charl...@visi.com Minneapolis, MN http://charles.robinsontwins.org http://www.facebook.com/charles.robinson -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: simple-as-dirt focus calibration method
On 04/04/2012 12:56 PM, Bryan Jacoby wrote: Can anybody explain the origin of lens-related phase detection AF errors? Pixel peeping. -- William Robb -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
