{"id":364,"date":"2007-01-23T21:45:10","date_gmt":"2007-01-23T12:45:10","guid":{"rendered":"https:\/\/regex.info\/blog\/photo-tech\/focus-chart"},"modified":"2007-01-23T21:45:10","modified_gmt":"2007-01-23T12:45:10","slug":"focus-chart","status":"publish","type":"page","link":"https:\/\/regex.info\/blog\/photo-tech\/focus-chart","title":{"rendered":"Jeffrey&#8217;s Autofocus Test Chart"},"content":{"rendered":"\n\n<div class='ic'><a href='\/i\/JEF_024811.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024811_sm.jpg\" width=\"532\" height=\"480\"\nalt=\"Jeffrey's Autofocus Test Chart, on a clipboard, in the light by a\nwindow\"\nid=\"i024811\"\ntitle=\"Jeffrey's Autofocus Test Chart, on a clipboard, in the light by a\nwindow\"\/><\/a><br\/><span class=\"robots-nocontent\" style='color:#BBB; font-size:85%'>Nikon D200 + 70-200mm f\/2.8 @ 70mm\n&mdash; <sup>1<\/sup><big>\/<\/big>320 sec, f\/2.8, ISO 400 &mdash; <a\nclass='quiet' style='color:#77B'\nhref='\/imageinfo.cgi?url=http%3A%2F%2Fregex.info%2Fi%2FJEF_024811.jpg'>full\nexif<\/a><\/span><br\/><span style='font-size:175%'>Testing SLR Autofocus<\/span><\/div>\n\n<p>\n\nThis post describes an autofocus test chart I've developed, why <span class='nobr'>I think<\/span>\nit's better than others I've seen, and how to use it to test the autofocus\nof your camera and lens:\n\n<\/p>\n<!--TECH-->\n<div class=\"robots-nocontent\" style=\"border: 2px solid #FF8080;\n            float: right;\n            padding: 0 1em 1em 1em;\n            margin: 10px 0 1em 1em;\n            display: inline;\">\n<p style='white-space: nowrap'><b>My Tech-Related Photography Posts<\/b><\/p>\n<ul style='margin:0; font-size:80%'>\n  <li><a href='\/blog\/lightroom-goodies\/ipad-howto2'>My Lightroom-to-iPad Workflow<\/a><\/li>\n  <li><a href='\/blog\/lightroom-goodies\/'>Lightroom Goodies<\/a> (lots of plugins)<\/li>\n  <li><a href='\/blog\/photo-tech\/color-spaces-page1\/'>Digital Image Color Spaces<\/a><\/li>\n  <li><a href='\/blog\/other-writings\/online-exif-image-data-viewer\/'>Online Exif (Image Data) Viewer<\/a><\/li>\n  <li><a href='\/blog\/photo-tech\/focus-chart\/'>Jeffrey's Autofocus Test Chart<\/a><\/li>\n  <li><a href='\/blog\/photo-tech\/calendar\/'>Photoshop Calendar-Template-Building Script<\/a><\/li>\n  <li><a href='\/blog\/lightroom-goodies\/ipad-howto'>How to Prepare Photos for an iPad<\/a><\/li>\n  <li><a href='\/blog\/photo-tech\/nef-compression\/'>A Qualitative Analysis of NEF Compression<\/a><\/li>\n  <li><a href='\/blog\/2007-08-24\/554'>Tripod Stability Tests<\/a><\/li>\n<\/ul>\n<p style='font-size:85%; margin:10px 0 0 0'><a href=\"\/blog\/photo-tech\/\">more<\/a>...<\/p>\n<\/div>\n<!--\/TECH-->\n\n\n<ol>\n  <li><a href='#intro'>Introduction<\/a><\/li>\n  <li><a href='#features'>What Makes <span class='nobr'>a Good<\/span> Test Chart<\/a><\/li>\n  <li><a href='#print'>How to Print It<\/a> (downloading offered here)<\/li>\n  <li><a href='#prepare'>Preparing to Use It<\/a><\/li>\n  <li><a href='#shot'>Taking the Shot<\/a><\/li>\n  <li><a href='#interpret'>Interpreting the Results<\/a><\/li>\n<\/ol>\n\n\n<h2>1. <a name='intro'>Introduction<\/a><\/h2>\n\n<p>\n\nIf you suspect that your modern SLR or SLR lens has autofocus problems, you\ncan use <span class='nobr'>a chart<\/span> like the one offered on this page to perform some tests.\n\n<\/p><p>\n\nThe basic premise of a chart like this is that when photographed at an\nangle, the paper slices through the plane of focus. Depending on the\nsituation, that plane can be very thick, encompassing the whole chart\n(leaving the whole chart in focus), or, more usefully, it can be very thin,\nleaving only the areas of the chart that intersect with that thin region in\nfocus.\n\n<\/p><p>\n\nThe illustration below shows proper autofocus and the result one might\nexpect from it, where the region of what is actually in focus is more or\nless centered on the focus target. <span class='nobr'>It also has<\/span> views for the problems of\n<i>back focus<\/i> and <i>front focus<\/i>, where for some reason, the lens\nactually focuses on <span class='nobr'>a region<\/span> either behind or in front of the focus point\n(resulting in the in-focus area on the chart to be above or below the focus\ntarget). Mouseover the buttons under the chart to see those views.\n\n<\/p>\n\n\n<table align='center' border='0' cellpadding='0' cellspacing='0' style='margin-top:15px; border:solid gray 1px; margin-bottom:40px'><tr valign='top'><td>\n  <div style='height:297px; width:450px; position:relative; padding-bottom:4px'>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartBasic-BackFocus.gif\" width=\"450\" height=\"297\"\nalt='Illustration of autofocus problem \"back focus\"'\nclass=\"raw\"\nid=\"img653_1\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle='Illustration of autofocus problem \"back focus\"'\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartBasic-ProperFocus.gif\" width=\"450\" height=\"297\"\nalt=\"Illustration of properly working autofocus\"\nclass=\"raw\"\nid=\"img653_2\"\nindexhint=\"right\"\nstyle=\"position:absolute; left:0; top:0; display:block\"\ntitle=\"Illustration of properly working autofocus\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartBasic-FrontFocus.gif\" width=\"450\" height=\"297\"\nalt='Illustration of the autofocus problem \"front focus\"'\nclass=\"raw\"\nid=\"img653_3\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle='Illustration of the autofocus problem \"front focus\"'\/>\n  <\/div>\n\n   <div align='center' style='margin-bottom: 10px'>\n                              <span class='b653' id='but653_1' onmouseover='OnMouse653(1)'>Back Focus<\/span>\n    &nbsp;&nbsp;-&nbsp;&nbsp; <span class='b653' id='but653_2' onmouseover='OnMouse653(2)'>Proper Focus<\/span>\n    &nbsp;&nbsp;-&nbsp;&nbsp; <span class='b653' id='but653_3' onmouseover='OnMouse653(3)'>Front Focus<\/span>\n     <p style='margin-top:5px; font-size: small'>mouseover <span class='nobr'>a button<\/span> to see that view<\/p>\n   <\/div>\n   <div style='padding-bottom:0; margin-bottom:0; text-align:left; font-size:65%; opacity:.6; filter:alpha(opacity=60)'>&nbsp;&nbsp;(Camera side view from <a class='quiet' href='http:\/\/www.dpreview.com\/reviews\/nikond200\/page3.asp'>Digital Photography Review<\/a>)<\/div>\n\n\n<\/td><td>\n\n  <div style='background:#D2D2D2; height:350px; width:450px; position:relative; padding-bottom:20px'>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartResult-BackFocus.gif\" width=\"450\" height=\"350\"\nalt='Example of the autofocus problem \"back focus\"'\nclass=\"raw\"\nid=\"img652_1\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle='Example of the autofocus problem \"back focus\"'\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartResult-ProperFocus.gif\" width=\"450\" height=\"350\"\nalt=\"Example of properly working autofocus\"\nclass=\"raw\"\nid=\"img652_2\"\nindexhint=\"left\"\nstyle=\"position:absolute; left:0; top:0; display:block\"\ntitle=\"Example of properly working autofocus\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartResult-FrontFocus.gif\" width=\"450\" height=\"350\"\nalt='Example of the autofocus problem \"front focus\"'\nclass=\"raw\"\nid=\"img652_3\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle='Example of the autofocus problem \"front focus\"'\/>\n  <\/div>\n\n<\/td><\/tr><\/table>\n\n<h3>It has to be said....<\/h3>\n\n<p>\n\nIt must be said on a page like this that while there is certainly broken or\nmiscalibrated equipment out there, it's probably safe to say that the\nmajority of &#8220;is my autofocus broken?&#8221; concerns are rooted not\nin miscalibrated equipment, but in the user's misunderstanding of the\nequipment, or of proper technique.\n\n<\/p><p>\n\nIf you suspect you have equipment with autofocus problems and mention it on\n<span class='nobr'>a photography<\/span> forum, such as those at Phil Askey's most excellent <a\nhref='http:\/\/dpreview.com\/'>Digital Photography Review<\/a>, be prepared for\nthree types of responses: &#8220;me too&#8221;, &#8220;are you\nsure?&#8221;, and &#8220;it's all your fault.&#8221;\n\n<\/p><p>\n\nAbout that last group, sadly, some people seem to enjoy being combative and\nignore all evidence that the user actually does understand the issues at\nhand, and persistently, incessantly post &#8220;it's all your fault &ndash;\nyou don't understand anything&#8221; type responses. Just ignore them.\n\n<\/p><p>\n\nHowever, the &#8220;are you sure, did you consider...&#8221; responses tend\nto be from respectable forum members trying to help. Even if it does turn\nout that your equipment is at fault, you can always pick up good hints and\ntips from these people, so embrace and appreciate them. <span class='nobr'>I certainly<\/span> learned\n<span class='nobr'>a lot<\/span> when <span class='nobr'>I went<\/span> through this with my own autofocus problems. <span class='nobr'>It turns<\/span> out\nthat the major cause of my problems was <a\nhref='\/blog\/2007-01-19\/363'>broken equipment<\/a>, but in\ntrying to understand where the problem lay, <span class='nobr'>I learned<\/span> <span class='nobr'>a lot<\/span> and improved my\ntechnique.\n\n<\/p><p>\n\nOh, and I came up with an excellent autofocus test chart....\n\n<\/p>\n\n<div style='float:right; padding-bottom:10px; margin: 20px 0 10px 3em; text-align:center'>\n  <div style='height:513px; width:383px; position: relative; z-index:1; margin-bottom:10px'>\n  <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/focuschart-v1.0-sm.png\" width=\"383\" height=\"513\"\nalt=\"Jeffrey's Autofocus Test Chart (mini thumbnail version)\"\nclass=\"raw\"\nid=\"img567_1\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:block; width:383px; height:513px\"\ntitle=\"Jeffrey's Autofocus Test Chart (mini thumbnail version)\"\/>\n  <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/focuschart-v1.0-sm2.png\" width=\"383\" height=\"513\"\nalt=\"Jeffrey's Autofocus Test Chart (illustration of what the autofocus system sees)\"\nclass=\"raw\"\nid=\"img567_2\"\nstyle=\"position:absolute; left:0; top:0; display:none; width:383px; height:513px\"\ntitle=\"Jeffrey's Autofocus Test Chart (illustration of what the autofocus system sees)\"\/>\n  <\/div>\n\n  <style type=\"text\/css\">\n  span.b653 { padding:2px 6px; border:gray 1px solid }\n  span.b567 { padding:2px 6px; border:gray 1px solid; margin-bottom:10px }\n  .b773     { margin: 2px 0px; border:#EFE 1px solid }\n  div.ex773 { margin-top:30px; margin-bottom:50px; border:solid 1px #686; padding: 0px 30px 30px 30px; text-align:center; font-size: 150% }\n  div.ex773 div.ic { margin-bottom:15px !important  }\n  <\/style>\n  <center>\n    <span class='b567' id='but567_1' onmouseover='OnMouse567(1)'>What You See<\/span>\n   &nbsp;&nbsp;&nbsp;&nbsp;\n    <span class='b567' id='but567_2' onmouseover='OnMouse567(2)'>What the Autofocus Sees<\/span>\n    <br\/>\n    <small>mouseover <span class='nobr'>a button<\/span> to see that image<\/small>\n  <\/center>\n<\/div>\n\n\n<h2>2. <a name='features'>What Makes <span class='nobr'>a Good<\/span> Test Chart?<\/a><\/h2>\n\n<p>Many factors make an autofocus test chart good or bad, but the two most\noverwhelmingly important are:<\/p>\n\n<ol>\n  <li>the ability to ensure that the autofocus locks on to the exact\n      location you intend, and<\/li>\n\n  <li>that it allows you to clearly interpret <b>relative<\/b> crispness of\n      focus across the scene.<\/li>\n\n<\/ol>\n\n<p>Without the first, the test has absolutely no meaning, and without the\nsecond, you can't grasp the meaning it holds.<\/p>\n\n\n<p>Two popular autofocus test charts I've seen and used (and learned much\nfrom), by Tim Jackson (no longer online) and <a href='http:\/\/www.leongoodman.com\/d70focusnew.html'>Leon\nGoodman<\/a>, don't address either of these concerns as well as they could,\nwhich is why <span class='nobr'>I developed<\/span> the chart presented here.<\/p>\n\n<div style='border:solid 1px red; padding: 10px 1em; color:#B08888'>\n<p><b>Update (December 2008)<\/b> &mdash; If you'd like to do serious focus-related lens calibration, also consider\nthe\n<a href='http:\/\/michaeltapesdesign.com\/lensalign.html'>LensAlign Focus Calibration System<\/a> from the Michael Tapes Design,\nthe makers of the WhiBal.\n<\/p><p>\n<span class='nobr'>I consulted<\/span> with them on the product during its design\n(&#8220;consulted&#8221; in the &#8220;had discussions and lent my expertise and opinions&#8221; sense, not the &#8220;got paid for my time&#8221; sense, though they did kindly give me one),\nand believe it's <span class='nobr'>a fantastic<\/span> tool for lens testing and calibration.\n<\/p><p><span class='nobr'>It's better<\/span> than my chart in every metric... except price. \ud83d\ude42<\/p><\/div>\n\n\n\n<p>I'll go ahead and add a third important characteristic of <span class='nobr'>a good<\/span> test chart\n&ndash; perhaps the most important &ndash; <b>proper instructions<\/b>,\nbecause it's easy to draw the wrong conclusions from an improperly used\nchart. <span class='nobr'>The two charts<\/span> <span class='nobr'>I link<\/span> to in the previous paragraph excel in this\narea, and reading through them is highly recommended.<\/p>\n\n\n<h3>Ensuring Autofocus Lock<\/h3>\n\n<p>Toward the first goal, the middle my test chart has <span class='nobr'>a high<\/span>-contrast\nblack bar &ndash; the autofocus target &ndash; surrounded on all sides by\nliberal expanses of low-contrast gray that the camera autofocus can not\nlock on to. <span class='nobr'>For an illustration<\/span> of this, see the &#8220;What the Autofocus\nSees&#8221; button in the super-shrunk view of the chart, at right.\n\n<\/p><p>\n\n(Testing to ensure that your camera's autofocus system can indeed\n<b>not<\/b> lock onto the low-contrast gray is an important step in <a\nhref='#prepare'>Preparing to Use<\/a> the chart.)\n\n<\/p><p>\n\nBelow is a small section of the chart at full resolution, from slightly\nleft of center, showing part of the black bar that is the focus target\n(with the red line added here just to indicate the vertical centerline of\nthe chart).\n\n<\/p>\n<br clear='all'\/>\n\n<img loading=\"lazy\" decoding=\"async\" src=\"\/i\/focuschart-v1.0-c.png\" width=\"642\" height=\"343\"\nalt=\"Full-resolution section from Jeffrey's Autofocus Test Chart\"\nclass=\"ic raw\"\nid=\"ifocuschart_v1_0_c\"\ntitle=\"Full-resolution section from Jeffrey's Autofocus Test Chart\"\/>\n\n<p>However, here's what the autofocus sees:<\/p>\n\n<img loading=\"lazy\" decoding=\"async\" src=\"\/i\/focuschart-v1.0-c2.png\" width=\"642\" height=\"350\"\nalt=\"Full-resolution section illustrating how an autofocus system sees Jeffrey's Autofocus Test Chart\"\nclass=\"ic raw\"\nid=\"ifocuschart_v1_0_c2\"\nindexhint=\"noindex\"\ntitle=\"Full-resolution section illustrating how an autofocus system sees Jeffrey's Autofocus Test Chart\"\/>\n\n<p>This provides a clear target for the autofocus. The low-contrast gray\nextends quite <span class='nobr'>a bit<\/span> from side to side, but more importantly, it extends the\nfull height of the page. This means that even when the chart is viewed at <span class='nobr'>a\nsteep<\/span> angle like that shown in the photo at the top of this page, <span class='nobr'>a large<\/span>\narea of low-contrast gray still presents itself around the target,\nbuffering it from anything else that the autofocus might lock on. Thus,\nwith the precautions discussed later, you're sure that the autofocus locks\nonto the target bar if it locks onto anything at all.<\/p>\n\n<h3>Ease of Interpretation<\/h3>\n\n<p>Toward the second important feature &ndash; allowing you to interpret\nrelative focus &ndash; I've filled the area around the target with lines\nand boxes that, when viewed at an angle, make it quite clear how focus\nprogresses as you inspect up and down the page:<\/p>\n\n\n<div class='ic'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024818_c1.jpg\" width=\"670\" height=\"280\"\nalt=\"An example of perfect autofocus, as seen with\nJeffrey's Autofocus Test Chart\"\nid=\"i024818_c1\"\nindexhint=\"noindex\"\ntitle=\"An example of perfect autofocus, as seen with\nJeffrey's Autofocus Test Chart\"\/><br\/><span class=\"robots-nocontent\" style='color:#BBB; font-size:85%'>Nikon D200 + <span class='nobr'>Nikkor\n17<\/span>-55 f\/2.8 @ 55mm &mdash; <sup>1<\/sup><big>\/<\/big>1250 sec, f\/2.8, ISO 400\n&mdash; <a class='quiet' style='color:#77B'\nhref='\/imageinfo.cgi?url=http%3A%2F%2Fregex.info%2Fi%2FJEF_024818_c1.jpg'>full\nexif<\/a><\/span><\/div> <!-- JEF_024818.NEF: AF-S 55mm @ f\/2.8, 0.5 meters\naway: 0.7 centimeters (0.3 | 0.3) -->\n\n<p>\n\nIt should be readily apparent how useful the lines and blocks are when\nviewed this way, but it's perhaps useful to contrast this with <span class='nobr'>a different<\/span>\nmethod I've seen.\n\n<\/p><p>\n\nI've seen autofocus test charts that use lines of random <a\nhref='http:\/\/en.wikipedia.org\/wiki\/Lorem_Ipsum' class='quiet'>Lorem\nIpsum<\/a> text, because, as the author correctly notes, we are\nhypersensitive to the crispness of text, so it makes for good test fodder. <span class='nobr'>The problem<\/span> with this approach is that we don't really care about\n<i>absolute crispness<\/i>, but want to scan up and down to gauge\n<i>relative crispness<\/i>. For this, random lines of spaced text are not as\ngood because there's no continuity as you scan vertically.\n\n<\/p><p>\n\nOn the other hand, this chart's vertical lines make for something that\nwould be smooth and consistent throughout <span class='nobr'>a vertical<\/span> scan if focus were\nperfect throughout, but since focus is not perfect throughout, the smooth\nand consistent nature of the lines highlight clearly what is and isn't in\nfocus.\n\n<\/p><p>\n\nAdditionally, when some of the lines are dashed, the individual blocks\nmaking up the line become convenient visual markers of distance from the\nfocus target, allowing you to quickly compare <span class='nobr'>a block<\/span> <i>above<\/i> the\ntarget with its counterpart the same distance <i>below<\/i> the target.\n\n<\/p>\n\n<h2>3. <a name='print'>How to Print The Test Chart<\/a><\/h2>\n\n<p>\n\nThe test charts are provided as 2,449 &times; 3,299 pixel grayscale GIFs,\nwhich, when printed at 300 <span style='font-variant:\nsmall-caps'>ppi<\/span>, fit nicely on US Letter or A4-sized paper.\n\n<\/p><p>\n\nThe key to properly printing the test chart is to get <span class='nobr'>a result<\/span> in which the\ngray areas are faint enough that your camera's autofocus system can't lock\nonto them, but are distinct enough that you can use them to gauge the\nresults. With <b>my<\/b> printer on <b>my<\/b> paper in the light <b>I<\/b>\nuse for tests with <b>my<\/b> camera, &#8220;25% gray&#8221; seems to be the\nsweet spot.\n\n<\/p><p>\n\nYour situation may be different from mine, so I've built seven different\nversions of the test chart, each with differing levels of gray for the\nlow-contrast areas. The 5% version is the most faint, while the 35% is the\ndarkest:\n\n<\/p>\n\n<table cellpadding='10' style='padding:5px 30px; margin:30px auto; border: solid 1px #555; text-align:center'>\n<tr><td style='font-weight:bold; font-size:130%'>\nDownload Jeffrey's Autofocus Test Chart (version 1.0)\n<\/td><\/tr><tr><td>\n<span style='font-size:120%'><a href='\/i\/FocusChart-v1.0-gray05.gif'>5%<\/a>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<a href='\/i\/FocusChart-v1.0-gray10.gif'>10%<\/a>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<a href='\/i\/FocusChart-v1.0-gray15.gif'>15%<\/a>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<a href='\/i\/FocusChart-v1.0-gray20.gif'>20%<\/a>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<b><a href='\/i\/FocusChart-v1.0-gray25.gif'>25%<\/a><\/b>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<a href='\/i\/FocusChart-v1.0-gray30.gif'>30%<\/a>\n&nbsp;&nbsp;&middot;&nbsp;&nbsp;\n<a href='\/i\/FocusChart-v1.0-gray35.gif'>35%<\/a><\/span>\n<\/td><\/tr><tr><td style='padding-top:10px'>\n\nOn Windows, right-click the desired link, and on <span class='nobr'>a Mac,<\/span> ctrl-click the\nlink,<br\/>then select the &#8220;Save Target As&#8221; or &#8220;Download Linked\nFile&#8221; item to download the chart image.\n\n<\/td><\/tr><\/table>\n\n<p>\n\nI'll suggest that you start with the <a\nhref='\/i\/FocusChart-v1.0-gray25.gif'>25% version<\/a> that\nworked for me, printing and testing as instructed below, returning to try <span class='nobr'>a\nlower<\/span>-contrast version if need be.\n\n<\/p>\n<img loading=\"lazy\" decoding=\"async\" src=\"\/i\/Photoshop-ImageSize-300.png\" width=\"295\" height=\"361\"\nalt=\"Photoshop's 'Image Size' dialog\"\nclass=\"img_right ic raw\"\nid=\"iPhotoshop_ImageSize_300\"\nindexhint=\"noindex\"\nstyle=\"margin-left:1em\"\ntitle=\"Photoshop's 'Image Size' dialog\"\/>\n\n<p>\n\nBe sure to print at &#8220;100%&#8221; without any &#8220;fit to\npaper&#8221; option so that the resulting print is as crisp as your printer\ncan produce. <span class='nobr'>Any resizing<\/span> necessarily incurs fuzziness, which can make\ninterpretation of the results slightly more difficult.\n\n<\/p><p>\n\nIt makes sense to select the &#8220;center image on page&#8221; option, if your\nprint dialog offers it. Depending on the printer, you may have to select\nborderless printing in order to fit the full image onto the page, or just\nas well, let <span class='nobr'>a tad<\/span> be cropped off. Either are better than resizing to fit\nthe page.<\/p>\n\n<p>If printing from within Photoshop, be sure to tell Photoshop that it's\nto be printed at 300 <span style='font-variant: small-caps'>ppi<\/span> by\nselecting &#8220;Image <b>&gt;<\/b> Image Size...&#8221; and unchecking the\n&#8220;<b>Resample Image<\/b>&#8221; box, then change the <b>Resolution<\/b>\nto 300, as shown at right.<\/p>\n\n<p>If possible, print on high-resolution matte photo paper, such as Canon's\n<a href='http:\/\/www.amazon.com\/gp\/product\/B0000721Z3'>MP-101<\/a>. Besides\ngiving <span class='nobr'>a crisper<\/span> print, the paper is more sturdy, which makes it resistant\nto curling and warping (both of which are detrimental to its successful use\nin testing focus).<\/p>\n\n<p>After printing, test the appropriateness of the low-contrast gray by\nlighting the chart well, filling the viewfinder with the gray area, and\nchecking to see whether the autofocus can lock on to it. <span class='nobr'>If it can<\/span>, you\nneed to move to <span class='nobr'>a lower<\/span>-percent gray.<\/p>\n\n<p>The version you've printed holds promise if the autofocus system can't\nlock onto the gray, but the quick test you've just done is only\npreliminary. <span class='nobr'>Be sure to<\/span> check again under actual conditions after setting up\nfor the real shot, as described below.<\/p>\n\n\n<h2>4. <a name='prepare'>Preparing to Use It<\/a><\/h2>\n\n<p>Using the test chart involves taking <span class='nobr'>a picture<\/span> of it, but it's important\nthat it's done under the right conditions.<\/p>\n\n<h3>The Setup<\/h3>\n\n<ul>\n  <li><p><b>Bright<\/b> &mdash; you want enough light for the autofocus\n   system to do its job, and to allow for <span class='nobr'>a fast<\/span> enough shutter speed, to\n   reduce overall shake-induced blur.<\/p><\/li>\n\n  <li><p><b>Wide open aperture<\/b> &mdash; the wider the aperture (that is, the lower the f-stop number), the more shallow the\n       depth of field becomes, thereby accentuating any focus-related\n       problems. Using aperture-priority exposure mode makes this easy to\n       ensure.<\/p><\/li>\n\n  <li><p><b>Autofocus On<\/b> &mdash; lest you forget \ud83d\ude42<\/p><\/li>\n\n  <li><p><b>Fast Shutter<\/b> &mdash; you want <span class='nobr'>a fast<\/span> enough shutter speed\n       to eliminate the blurring effects of camera shake. <span class='nobr'>As one suggestion<\/span>,\n       you should have enough light to get at least a\n       <sup>1<\/sup>\/1,000<sup>th<\/sup> second exposure at ISO 400 or lower. (That should cover most bases, but if you're\n       skilled enough to think this page might be useful, you're probably skilled enough to know what shutter speed you need\n       to eliminate shake-induced blur.)\n   <\/p><p>\n       You might also consider using <span class='nobr'>a tripod,<\/span> and <span class='nobr'>a remote<\/span> shutter release.<\/p><\/li>\n\n  <li><p><b>IS? \/ VR?<\/b> &mdash; I've never heard of an\n       image-stabilization or vibration-reduction feature causing\n       changes in focus accuracy, but just in case, if you have equipment\n       with these features, it might make sense to test both with and without them.<\/p><\/li>\n\n  <li><p><b>Low ISO<\/b> &mdash; the ISO sensitivity is not particularly important in its own right, but it's important to realize\n       that while increasing it allows you to get more sensitivity from the\n       sensor, but it does nothing for the autofocus system. <span class='nobr'>If you know<\/span> you have <b>plenty<\/b> of\n       light for the autofocus system and merely want to push the shutter speed really high, increasing ISO\n       is fine. Just realize that pushing it too high adds some level of noise-induced blur to the overall picture.\n\n       <\/p><p>\n\n       Personally, I like to keep the ISO under 400 on my Nikon D200, but I'll go to 800 if needed when doing <span class='nobr'>a quick<\/span> focus test\n       that I'll not put <i>too<\/i> much stock in.\n\n       <\/p><\/li>\n\n  <li><p><b>Square to the Chart<\/b> &mdash; it makes interpretation easier\n       if you're exactly square to the bottom of the chart (that is, you're\n       aiming straight to the chart on the horizontal plane, without any side-to-side angle).\n       The top-center and bottom-center of\n       the chart has small black &#8220;sightlines&#8221; that can be of help.<\/p><\/li>\n\n\n  <li><p><b>Chart is Flat<\/b> &mdash; if the chart is not perfectly flat, its slight rumples can have <span class='nobr'>a large<\/span> impact on\n       the focus. <span class='nobr'>It's okay if<\/span> just the corners of\n       the chart float <span class='nobr'>a bit<\/span> off the table. <span class='nobr'>The focus<\/span> is on the main part of the chart, so to speak, and that's the section\n       that must be perfectly flat.) Using <span class='nobr'>a heavy<\/span>-stock paper helps <span class='nobr'>a lot.<\/span><\/p><\/li>\n\n  <li><p><b>Exposure Compensation<\/b> &mdash; especially in really bright light (e.g. direct sun), automatic exposure tends to\n       underexpose the fairly uniform brightness of the chart, so you may need to dial in some compensation. <span class='nobr'>A few sample<\/span> shots\n       should make it clear whether this is necessarily.<\/p><\/li>\n\n  <li><p><b>Enough Distance<\/b> &mdash; nothing will work if you're closer\n       than the minimum focus distance of the lens, so be sure that you're far\n       enough away that you're not bumping up against that limit. Note that some\n       lenses have <span class='nobr'>a different<\/span> minimum-focus-distance between manual focus and\n       autofocus. Zoom lenses can have <span class='nobr'>a different<\/span> minimum depending upon\n       the focal length in use.<\/p><\/li>\n\n<\/ul>\n\n<p>Deciding how far away you should be from the chart is influenced by what\nkind of test you want (some lenses display autofocus accuracy that varies\nwith subject distance), the focal length of the lens, and the nature of\nyour autofocus sensors.<\/p>\n\n<h3>Understanding Your Autofocus Sensors<\/h3>\n\n<p>It's possible that the active area of the camera's autofocus sensor\nexactly matches the indicator you see in the viewfinder, but it's not\nlikely. More likely is that the active area of detection is <span class='nobr'>a bit<\/span> larger,\nperhaps asymmetrically so.<\/p>\n\n<p>The photo sequences below illustrate the pitfalls of not understanding\nyour camera's autofocus sensors. The right-hand image is just <span class='nobr'>a closeup<\/span> of\nthe central part of the full-frame left-hand image. Mouseover the four\ndescriptions below the pictures to see the story unfold...<\/p>\n\n<table align='center' border='0' cellpadding='9' cellspacing='0' style='margin-top:15px; border: solid gray 1px'>\n  <tr><td colspan='2'><span style='font-size:150%; font-weight:bold'>&nbsp;&nbsp;Improperly Performed Test<\/span><\/td><\/tr>\n\n<tr valign='top' align='center'><td>\n  <div style='height:295px; width:440px; position:relative; border:solid 4px black; margin-bottom:10px'>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide1a.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 1 of 4\"\nclass=\"raw\"\nid=\"img773_1\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:block\"\ntitle=\"Improperly performed autofocus test, step 1 of 4\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide1b.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 2 of 4\"\nclass=\"raw\"\nid=\"img773_2\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 2 of 4\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide1c.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 3 of 4\"\nclass=\"raw\"\nid=\"img773_3\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 3 of 4\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide1d.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 4 of 4\"\nclass=\"raw\"\nid=\"img773_4\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 4 of 4\"\/>\n  <\/div>\n  <span style='font-size:130%; font-weight:bold'>Full Frame<\/span>\n  <\/td><td>\n  <div style='height:295px; width:440px; position:relative; border:solid 4px gray; margin-bottom:10px'>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide2a.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 1 of 4 (close-up view)\"\nclass=\"raw\"\nid=\"img772_1\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:block\"\ntitle=\"Improperly performed autofocus test, step 1 of 4 (close-up view)\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide2b.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 2 of 4 (close-up view)\"\nclass=\"raw\"\nid=\"img772_2\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 2 of 4 (close-up view)\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide2c.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 3 of 4 (close-up view)\"\nclass=\"raw\"\nid=\"img772_3\"\nindexhint=\"noindex\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 3 of 4 (close-up view)\"\/>\n    <img loading=\"lazy\" decoding=\"async\" src=\"\/i\/FocusChartWide2d.jpg\" width=\"440\" height=\"295\"\nalt=\"Improperly performed autofocus test, step 4 of 4 (close-up view)\"\nclass=\"raw\"\nid=\"img772_4\"\nindexhint=\"right\"\nstyle=\"position:absolute; left:0; top:0; display:none\"\ntitle=\"Improperly performed autofocus test, step 4 of 4 (close-up view)\"\/>\n  <\/div>\n  <span style='font-size:130%; font-weight:bold'>Closeup View<\/span>\n  <\/td><\/tr>\n\n  <tr><td colspan='2'>\n    <ol>\n    <li class='b773' id='but773_1' onmouseover='OnMouse773(1)'>&nbsp;Scene with my camera's autofocus target indicator, over the focus target.<\/li>\n    <li class='b773' id='but773_2' onmouseover='OnMouse773(2)'>&nbsp;Focus point <span class='nobr'>I intended<\/span> to be chosen (marked with purple star) and intended in-focus region (green band)<\/li>\n    <li class='b773' id='but773_3' onmouseover='OnMouse773(3)'>&nbsp;Orange region shows actual active area of my camera's autofocus sensor<\/li>\n    <li class='b773' id='but773_4' onmouseover='OnMouse773(4)'>&nbsp;Possible focus point chosen by camera (purple star) and resulting in-focus region (green band). Unexpected!<\/li>\n    <\/ol>\n<\/td><\/tr>\n<\/table>\n\n<p>\n\nThe final result above appears as if the camera\/lens has back focus, but in\nreality, it's just picking an unexpected spot to focus on. <span class='nobr'>It would<\/span> be nice\nif the indicator in the viewfinder exactly matched the active area, but\nsince that's not the case, it behooves you to understand your sensors.\n\n<\/p><p>\n\nI should be clear that the illustration above is just to make <span class='nobr'>a point,<\/span> and\nit's unlikely that any camera actually has an autofocus sensor shaped like\nthat shown in steps 3 and 4.\n\n<\/p><p>\n\nI'll leave the detailed description of mapping your autofocus sensors to\nthe link in the previous paragraph, but in short, one way to measure the\nactive area is to get close enough to the chart so that the low-contrast\ngray area fills the width of the viewfinder, and place the sensor indicator\nright in the middle of it. Having nothing high-contrast anywhere nearby, it\nshouldn't be able to lock onto <span class='nobr'>a focus,<\/span> but instead, should hunt around\nuntil it gives up. (If it can lock onto the low-contrast gray areas, you'll\nneed to use one of the lower-percent gray versions offered in the <a\nhref='#print'>How to Print It<\/a> section.)\n\n<\/p><p>\n\nThen, as you move the aim toward the high-contrast black running up and\ndown the sides of the chart, keep trying the autofocus, and once it's able\nto lock on, note where the black begins relative to that edge of the sensor\nindicator. <span class='nobr'>You can do<\/span> the same moving the other way, and up and down, and\nso &#8220;map&#8221; the true active area of your sensor.\n\n<\/p><p>\n\nIf you have multiple sensors, they may well each have their own\ncharacteristics, so you may wish to map them all, but for the purposes of\ntesting your autofocus system, it's sufficient to use only the middle\nsensor.\n\n<\/p><p>\n\nOf course, the more you can fill the viewfinder with the chart, the better.\nEven if the scenario above results in <span class='nobr'>a valid<\/span> test, chart is too small to\nreally make out much detail from it, even with the resolution my\n10-megapixel SLR affords.\n\n<\/p>\n\n<h2>5. <a name='shot'>Taking the Shot<\/a><\/h2>\n\n<p>\n\nAfter taking into account everything in the previous section, it's <span class='nobr'>a simple<\/span>\nmatter to take some shots. Take multiple shots at different angles of\nattack. <span class='nobr'>A lower<\/span> angle shows the depth of the in-focus field the most\nclearly (and with it, the accuracy of the autofocus system), but requires\nthe most care to ensure that the autofocus sensor does not see the top of\nthe chart instead of the intended target.\n\n<\/p><p>\n\n(There's an example of a valid test with very low angle of attack in the next section.)\n\n<\/p><p>\n\nWhile shooting, keep the following in mind:\n\n<\/p>\n\n<ul>\n      <li><p>Keep double-checking that you're square to the chart<\/p><\/li>\n\n      <li><p>Be very careful not to allow yourself to move the camera\n             between achieving focus lock and actually taking the picture. Some people, for example,\n             have an unconscious habit to move forward <span class='nobr'>a half<\/span> an inch in the\n             process of taking the shot, and such movement would absolutely destroy any\n             meaning to this test.<\/p><\/li>\n\n      <li><p>If you're near the minimum-focus distance of the lens, keep that in mind as well.<\/p><\/li>\n\n      <li><p>Pause occasionally to double-check that the autofocus can't lock on the\n           low-contrast gray (by pointing at the wide expanse of it in the upper half\n           of the chart and confirming that focus can't be found.)<\/p><\/li>\n\n<\/ul>\n\n<p>Once I've set up for a particular shot, <span class='nobr'>I take it<\/span>, then point the camera\nat something far and autofocus there, then return to autofocus on the\nchart, taking <span class='nobr'>a second<\/span> shot. <span class='nobr'>I then do<\/span> the same with something near (if I'm\nnot already near the minimum-focus distance of the lens) and return for <span class='nobr'>a\nthird<\/span> shot. This way, <span class='nobr'>I feel sure<\/span> that the autofocus is starting from\nscratch each time.<\/p>\n\n<p>I got used to taking multiple shots set up the same way because my lens\nwas giving somewhat random results. <span class='nobr'>I guess<\/span> that's one symptom of being\nbroken, because after <a href='\/blog\/2007-01-19\/363'>it\nwas fixed<\/a>, the results were consistently spot on.<\/p>\n\n<h2>6. <a name='interpret'>Interpreting the Results<\/a><\/h2>\n\n<p>After taking the shots, I load them into <a\nhref='http:\/\/www.adobe.com\/products\/photoshoplightroom\/'>Adobe Lightroom<\/a>\nand make <span class='nobr'>a couple<\/span> of quick adjustments to make the results <span class='nobr'>a bit<\/span> easier to\nsee (<span class='nobr'>I convert<\/span> them to grayscale, and adjust the contrast <span class='nobr'>a bit<\/span> to\naccentuate the low-contrast region). Lightroom is excellent for this\nbecause it lets me quickly zoom and pan on an image (more quickly even than\nPhotoshop), and to quickly flip back and forth among multiple images.<\/p>\n\n<p>In interpreting the results, I look at both the vertical progression of\nthe lines, and the numbers that run up and down the sides. Consider this example:<\/p>\n\n<div class='ic'><a href='\/i\/JEF_024834.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024834_sm.jpg\" width=\"700\" height=\"222\"\nalt=\"Perfect autofocus results, as seen with Jeffrey's Autofocus Test Chart\"\nid=\"i024834\"\nindexhint=\"noindex\"\ntitle=\"Perfect autofocus results, as seen with Jeffrey's Autofocus Test Chart\"\/><\/a><br\/><span class=\"robots-nocontent\" style='color:#BBB; font-size:85%'>Nikon D200 + <span class='nobr'>Nikkor 17<\/span>-55 f\/2.8 @ 55mm &mdash; <sup>1<\/sup><big>\/<\/big>3000 sec, f\/2.8, ISO 100 &mdash;\n<a class='quiet' style='color:#77B' href='\/imageinfo.cgi?url=http%3A%2F%2Fregex.info%2Fi%2FJEF_024834.jpg'>full exif<\/a><\/span><br\/><span\nstyle='font-size:125%'>The Clear Area is Clearly Clear<\/span><\/div>\n\n<p>The depth of field here is only about 8 millimeters (<span class='nobr'>a third<\/span> of an\ninch), so it's fairly easy to see the effects on the chart as it slices\nthrough the in-focus region. <span class='nobr'>The more clearly<\/span> focused parts of the vertical\nlines seem to be properly centered on the target stripe, and comparable\nnumbers (e.g. the left-side &#8220;2&#8221; <b>above<\/b> the midline and the left-side\n&#8220;2&#8221; <b>below<\/b> the midline) seem to be about equally fuzzy.<\/p>\n\n<p>Actually, in this case, there might be the slightest bit more sharpness\nto the numbers above the midline, but it's so slight that it could well\nbe because the autofocus picked the top edge of the target stripe rather\nthan the bottom edge. That's how good the autofocus was with this shot.<\/p>\n\n<p>(Frankly, it could be that the <i>bottom<\/i> sets of numbers have the\nslight edge in sharpness.... the more <span class='nobr'>I stare,<\/span> the fuzzier\n<i>everything<\/i> becomes!)<\/p>\n\n<p>Let's look at another example...<\/p>\n\n<div style='margin-top:20px' class='ic'><a\nhref='\/i\/JEF_024835.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024835_sm.jpg\" width=\"700\" height=\"286\"\nalt=\"Perfect autofocus\nresults with a low angle-of-attack view of Jeffrey's Autofocus Test Chart\"\nid=\"i024835\"\ntitle=\"Perfect autofocus\nresults with a low angle-of-attack view of Jeffrey's Autofocus Test Chart\"\/><\/a><br\/><span class=\"robots-nocontent\" style='color:#BBB; font-size:85%'>Nikon D200 + <span class='nobr'>Nikkor 17<\/span>-55 f\/2.8 @ 17mm\n&mdash; <sup>1<\/sup><big>\/<\/big>6000 sec, f\/2.8, ISO 100 &mdash; <a\nclass='quiet' style='color:#77B'\nhref='\/imageinfo.cgi?url=http%3A%2F%2Fregex.info%2Fi%2FJEF_024835.jpg'>full\nexif<\/a><\/span><br\/><span style='font-size:125%'><span class='nobr'>A Low<\/span> Angle of\nAttack<\/span><\/div>\n\n<p>Here, the depth of field is almost 10 times larger (7.6 centimeters; 3\ninches), which makes it more difficult to draw conclusions from the\nvertical lines. <span class='nobr'>In this case<\/span>, <span class='nobr'>I focus<\/span> more on the numbers (haha, <span class='nobr'>I'm so witty<\/span>). Clicking through to the <a\nhref='\/i\/JEF_024835.jpg'>larger version<\/a> and comparing\nthe two &#8220;5&#8221; above with the two &#8220;5&#8221; below, they feel fairly close in their\nfuzziness, although the upper pair are <span class='nobr'>a bit<\/span> sharper. <span class='nobr'>In this case<\/span>, that's\nto be expected because we're close enough to the chart that the depth of\nfield is not evenly distributed in front of and behind the focus point:\nabout 3.5 centimeters are in front, and 4.1 behind.<\/p>\n\n<h3>Depth of Field Measurements<\/h3>\n\n<p>\n\nPedantically speaking, &#8220;Depth of Field&#8221; doesn't really refer to\nthe region that's &#8220;in focus&#8221;, but rather, &#8220;of acceptable\nfocus.&#8221; The difference reflects the fact that as you move in front or\nbehind the focus point, the focus starts tapering off immediately, and\ncontinues to do so indefinitely. What's considered &#8220;acceptable\nfocus&#8221; changes depending on the intended use and the resolution of\nthe medium capturing the image (that means, among other things, that the\ndepth-of-field calculations are camera dependent). <span class='nobr'>The current<\/span> Wikipedia\npage on <a href='http:\/\/en.wikipedia.org\/wiki\/Depth_of_field'>Depth of\nField<\/a> has <span class='nobr'>a good<\/span> presentation of the concepts.\n\n<\/p><p>\n\nMy <a\nhref='\/blog\/other-writings\/online-exif-image-data-viewer\/'>Online\nExif Viewer<\/a> reports on the depth of field if the image data contains\nall the requisite data required to compute it. Some of this data is in the\nMaker Notes section of metadata, which Photoshop strips, so for best\nresults, check with an original straight-out-of-the-camera image.\n\n<\/p>\n<h3><span class='nobr'>A Few<\/span> More Samples<\/h3>\n\n<p>Here are a few more samples to inspect. <span class='nobr'>As with most<\/span> images on this post\n(and on my blog, for that matter), clicking through on the image brings you\nto <span class='nobr'>a larger<\/span> version.<\/p>\n\n<div class='ex773'><div class='ic'><a href='\/i\/JEF_024909.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024909_sm.jpg\" width=\"730\" height=\"359\"\nalt=\"An example of autofocus back focus, as seen with Jeffrey's Autofocus Test Chart\"\nid=\"i024909\"\nindexhint=\"noindex\"\ntitle=\"An example of autofocus back focus, as seen with Jeffrey's Autofocus Test Chart\"\/><\/a><\/div>\n\n  <p>At first glance this one might appear to be okay because the target is\n  clearly focused, but comparing, for example, the lower-left &#8220;4&#8221; with the\n  upper-left &#8220;4&#8221;, shows that there's <span class='nobr'>a bit<\/span> of back focus here.<\/p>\n\n  <p>This was taken with a 200mm lens from <span class='nobr'>a medium<\/span>-close distance (about\n  three yards), which results in <span class='nobr'>a depth<\/span> of field evenly split on either side\n  of the focus point. <span class='nobr'>Had it been<\/span> taken with <span class='nobr'>a short<\/span> focal length at <span class='nobr'>a\n  close<\/span> distance, it's possible that the depth of field would start to skew more\n  toward the rear, and as such, <span class='nobr'>a result<\/span> like this might be expected. That's\n  not the case here, so this shows back focus.<\/p>\n<\/div>\n\n<div class='ex773'><div class='ic'><a href='\/i\/JEF_024936.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024936_sm.jpg\" width=\"730\" height=\"368\"\nalt=\"An example of severe autofocus front focus, as seen with Jeffrey's Autofocus Test Chart\"\nid=\"i024936\"\nindexhint=\"noindex\"\ntitle=\"An example of severe autofocus front focus, as seen with Jeffrey's Autofocus Test Chart\"\/><\/a><\/div> <p>Some pretty severe\nfront focus<\/p> <\/div>\n\n<div class='ex773'><div class='ic'><a href='\/i\/JEF_024924.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024924_sm.jpg\" width=\"730\" height=\"368\"\nalt=\"An example of autofocus front focus, as seen with Jeffrey's Autofocus Test Chart\"\nid=\"i024924\"\nindexhint=\"noindex\"\ntitle=\"An example of autofocus front focus, as seen with Jeffrey's Autofocus Test Chart\"\/><\/a><\/div> <p>Front focus<\/p>\n<\/div>\n\n<div class='ex773'><div class='ic'><a\nhref='\/i\/JEF_024927.jpg'><img loading=\"lazy\" decoding=\"async\" src=\"\/i\/JEF_024927_sm.jpg\" width=\"730\" height=\"361\"\nalt=\"An example of severe autofocus back focus, as seen with Jeffrey's Autofocus Test Chart\"\nid=\"i024927\"\nindexhint=\"noindex\"\ntitle=\"An example of severe autofocus back focus, as seen with Jeffrey's Autofocus Test Chart\"\/><\/a><\/div> <p>Severe back\nfocus<\/p> <\/div>\n\n<h2>7. Conclusion<\/h2>\n\n<p>I would expect that the only people who actually read this far are those\nsuffering from really bad autofocus problems, and are desperate to\nunderstand them. <span class='nobr'>You have my<\/span> sympathy, and <span class='nobr'>I hope<\/span> that my test chart and\nwhat I've so verbosely presented here are helpful.\n\n<\/p>\n\n<script type='text\/javascript'>\n  var img652 = new Array();\n  var img653 = new Array();\n  var but653 = new Array();\n\n  but653[1] = document.getElementById('but653_1');\n  but653[2] = document.getElementById('but653_2');\n  but653[3] = document.getElementById('but653_3');\n\n  img653[1] = document.getElementById('img653_1');\n  img653[2] = document.getElementById('img653_2');\n  img653[3] = document.getElementById('img653_3');\n  img652[1] = document.getElementById('img652_1');\n  img652[2] = document.getElementById('img652_2');\n  img652[3] = document.getElementById('img652_3');\n\n\n function OnMouse653(num)\n {\n   img652[num].style.display         = 'block';\n   img653[num].style.display         = 'block';\n   but653[num].style.borderColor     = '#FF4040';\n   but653[num].style.backgroundColor = '#808080';\n   but653[num].style.color           = 'white';\n   but653[num].style.borderWidth     = '2px';\n   but653[num].style.padding         = '1px 5px';\n\n   for (i = 1; i <= 3; i++) {\n      if (i != num) {\n          img652[i].style.display         = 'none';\n          img653[i].style.display         = 'none';\n          but653[i].style.borderColor     = 'gray';\n          but653[i].style.backgroundColor = '';\n          but653[i].style.borderWidth     = '1px';\n          but653[i].style.padding         = '2px 6px';\n          but653[i].style.color           = '';\n      }\n   }\n }\n OnMouse653(2);\n\n\n var img567 = new Array();\n var but567 = new Array();\n img567[1] = document.getElementById('img567_1');\n but567[1] = document.getElementById('but567_1');\n img567[2] = document.getElementById('img567_2');\n but567[2] = document.getElementById('but567_2');\n\n\n function OnMouse567(num)\n {\n   img567[num].style.display         = 'block';\n   but567[num].style.borderColor     = '#FF4040';\n   but567[num].style.backgroundColor = '#808080';\n   but567[num].style.color           = 'white';\n   but567[num].style.borderWidth     = '2px';\n   but567[num].style.padding         = '1px 5px';\n\n   for (i = 1; i < 3; i++) {\n      if (i != num) {\n          img567[i].style.display         = 'none';\n          but567[i].style.borderColor     = 'gray';\n          but567[i].style.backgroundColor = '';\n          but567[i].style.borderWidth     = '1px';\n          but567[i].style.padding         = '2px 6px';\n          but567[i].style.color           = '';\n      }\n   }\n }\n OnMouse567(1);\n\n  var img772 = new Array();\n  var img773 = new Array();\n  var but773 = new Array();\n\n  but773[1] = document.getElementById('but773_1');\n  but773[2] = document.getElementById('but773_2');\n  but773[3] = document.getElementById('but773_3');\n  but773[4] = document.getElementById('but773_4');\n\n  img773[1] = document.getElementById('img773_1');\n  img773[2] = document.getElementById('img773_2');\n  img773[3] = document.getElementById('img773_3');\n  img773[4] = document.getElementById('img773_4');\n  img772[1] = document.getElementById('img772_1');\n  img772[2] = document.getElementById('img772_2');\n  img772[3] = document.getElementById('img772_3');\n  img772[4] = document.getElementById('img772_4');\n\n\n function OnMouse773(num)\n {\n   img772[num].style.display         = 'block';\n   img773[num].style.display         = 'block';\n\n   but773[num].style.borderColor     = '#C66';\n   but773[num].style.backgroundColor = '#411';\n\n   for (i = 1; i <= 4; i++) {\n      if (i != num) {\n          img772[i].style.display         = 'none';\n          img773[i].style.display         = 'none';\n          but773[i].style.borderColor     = '#555';\n          but773[i].style.backgroundColor = '';\n      }\n   }\n }\n OnMouse773(1);\n\n<\/script>\n\n\n\n","protected":false},"excerpt":{"rendered":"<p> This post describes an autofocus test chart I've developed, why I think it's better than others I've seen, and how to use it to test the autofocus of your camera and lens: <\/p> Introduction What Makes a Good Test Chart How to Print It (downloading offered here) Preparing to Use It Taking the Shot Interpreting the Results 1. Introduction <p> If you suspect that your modern SLR or SLR lens has autofocus problems, you can use a chart like the one offered on this page to perform some tests. <\/p><p> The basic premise of a chart like this is [...]","protected":false},"author":1,"featured_media":0,"parent":251,"menu_order":0,"comment_status":"open","ping_status":"open","template":"","meta":{"footnotes":""},"_links":{"self":[{"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/pages\/364"}],"collection":[{"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/comments?post=364"}],"version-history":[{"count":0,"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/pages\/364\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/pages\/251"}],"wp:attachment":[{"href":"https:\/\/regex.info\/blog\/wp-json\/wp\/v2\/media?parent=364"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}