So you got your sigma lens but your pictures are coming out of focus. well you can calibrate your autofocus using a sigma USB Dock. Although you can make slight correction using your camera’s inner AF adjustment; sigma gives you flexibility to micro-adjust some of their lens series. when I got my sigma 18-35 art series lens I knew that it has some focusing issue. So I bough sigma USB Dock and here is how I adjusted my auto focus. To calibrate your lens you will need a sigma USB Dock a steady tripod, a measurement tape a bubble leveler, and lens calibration tool. You can get one of this from amazon for 4-5$, I have a link in the description below. and yeah, you will need some patience. First decide your working area, put lens calibration tool on steady surface and level it. Now put your camera on a steady tripod and level it using your tripod leveler and adjust the height so it focuses exactly on the calibration tool surface where you will be focusing. Sigma software has four difference focus distances where you have to adjust your focus each difference can adjusted from values between negative twenty to positive twenty and if you have a zoon lens like me, you will have to adjust the same thing four times at different zooming range. yeah, you will need some patience…. before starting any process, download the software, connect your lens using a USB Dock and update your latest firmware. Now, use your measure tape and set your focal distance as accurate as you can from the film plane of the camera. And also use as much light as you can, so you can use lowest ISO of the camera. put your camera into Auto-focus mode, use your optical view finder and use only center focusing point. And choose the lowest number or widest aperture of your lens. And now we are ready to take our first picture. If you have a DSLR with a good LCD screen, you can zoom in on the ruler, and see whether your lens is focusing correctly or not. Here in my picture, it should be focusing exactly on zero, but it is front focusing a little. So now I will disconnect the lens from the camera, put it on the USB dock and I will adjust the values in positive numbers. I would suggest to start with plus or minus five intervals every time, and when you get close focusing values, start looking your pictures in computer and adjust the values from there. Choose a proper place for this procedure, as you can see, my tripod is here; my calibration tool is on my table, my USB dock is attached to my laptop; that way I can just take a lens, take my SD card, put it on my laptop attach my lens to the USB dock, see my images, calibrate my lens and put it back. Also work on one focal distance at one time, at different focal lengths that way, you don’t have to move your tripod everytime. Once you start to shoot at longer focal distance at wider focal lengths it gets little confusing since your baseline in my case zero will be in focus anyway. At this point start bracketing your adjacent lines and work with them If your upper line is more in focus and next below one is not, then lens is back focusing. Infinity is where things get little difficult since calibration tool is little difficult to use. I tried to focus distance houses but then I used longest distance around my working area and I made some cross-mark manually. Also I would recommend to work with one focal distance at one time and then take some test shots around. and then move to next focusing distance. Some people say its geaky, some say its nerdy, I would say its tiresome but rewarding.