Easy way to use Sigma Dock for microadjustment

Started Feb 18, 2016 | Discussions thread
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Don_Campbell Senior Member • Posts: 2,643
Easy way to use Sigma Dock for microadjustment
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Sorry for the length, but I hope it's sufficiently detailed to help someone.

I bought my Sigma 150-600 C last June along with the Sigma USB Dock. At the time I had just purchased a Canon 7DMkII body. The lens was pretty darned good straight out of the box and I had a busy summer of shooting a peculiar and interesting peregrine falcon saga so I delayed wrestling with 16 points of focus fine tuning with the dock.

Waiting for the gear to arrive, I had looked online at discussions of using the dock and I was certain that I had seen that the numeric value of the dock adjustment was 2X the numeric value of the in-camera AF microadjustment. However, when I got serious about doing the microadjustment I found that nearly every story of dock adjustment involved back and forth and back again between the lens+camera and the lens+dock+computer. Most of those stories also dealt with added complexity of many photos plus store-bought software and focus targets.

Then there were stories about using "dot-tune" methods for doing the offset detection without photos.

Finally, I read Lee Jay's method:http://www.dpreview.com/forums/post/56998000

He did initial focus using Live View AF to get the accurate focus on the sensor, then switched to viewfinder and watched the focus distance reading in its window on the lens while triggering AF using the phase detection system. Based on the direction the focus indication moved he could know which direction to change the microadjustment in the dock and iteration back and forth to the dock allowed him to find the adjustment where movement was zero during phase detect AF or it was equally likely to be + and - using phase detect. No photos but a lot of back and forth to the dock.

I tried to find the original story I had read giving the 2:1 ratio for the Sigma adjustment compared to the in-camera adjustments for both Canon and Nikon. Instead I found several vague statements--all about using a 2X ratio, including a discussion here:

http://www.dpreview.com/forums/post/56675910

and including use of the FoCal/Reikan system with the 2X ratio successfully here for Nikon:

http://www.dpreview.com/forums/post/55354553

Other forum posts here and at Fred Miranda also cited 2X as the ratio so I decided go with that for a first go.

I decided to incorporate Lee Jay's "which direction" Live View / optical view method with the idea of getting the estimate for the magnitude of the adjustment number using the in-camera Canon adjustment number. The process of course assumes you set up the phase detect AF and Live View to get optimal focus of the target at the various distances.

  • My process is to start with 0 for the in-camera microadjustment number for each of the 16 Sigma Dock points of distance/focal length.
  • Focus in Live View using contrast, switch to optical view and watch for movement of the focus distance in the focus window when triggering the phase detect AF.
  • If there is movement, indicating an offset of focus in the phase detect system, I adjust the in-camera MFA to get a "Canon number" for adjustment, write it down on paper, re-zero the in-camera adjustment value and repeat for the next Sigma Dock point.
  • Enter the numbers into the Sigma Dock software using 2X the "Canon number." Write them to the lens and check with the camera at the same distances and focal lengths.

Notes:

Along the way, I modified the above version slightly: I would confirm sharp focus in Live View at 10X magnfication. I also would manually move focus away from the AF position in both directions and re-trigger focus several times to pick the most consist result. I did this instead of "dot-tune" because I found the dot-tune values so far apart and not centered on the most frequently obtained AF focus position. Basically, I trusted my multiple focus to pick best, most consistent focus value (position of the focus indicator in the window) more than I trusted dot-tune's number.

After I entered my 16 microadjustment values into the Sigma Optimization Pro software and wrote them to the lens, I checked the values in the camera again and found all but two or three to be quite good. Good, meaning that the position of the contrast AF focus distance and the phase detect distance were equal within variations on both sides small and equivalent. In other words repeating phase detect AF (or even contrast in Live View AF) 10 times for the same target distance and focal length gives a small variation in focus chosen but that variation is distributed randomly around a "best focus" value that was the same for the Live View contrast AF and the optical view phase detect AF.

The 2-3 values (I forget already) that were still off might have been done when light was fading late in the afternoon when I first got the numbers--I redid the adjustment for them and all 16 distances/focal lengths were then properly adjusted. Weather has been terrible for photography so I haven't tried it on my favorite birds yet.

For a target I made a grid of horizontal and vertical lines of random width and spacings about 5x5 inches and printed it on card stock which I then taped to the side of a box so I could easily move it while keeping the camera stationary. For "infinity" I'm a bit challenged at my house since we're pretty much surrounded by NW forest of tall trees. The best I could find for infinity was an insulator at the top of lamp post which google earth tells me is ~125 yards away from my deck.

[Added in edit] I found an opening in the foliage of the trees through which I could spot the peak of a building that google earth says is 417 yards from my deck. That brings the focus mark at 600mm closer to the infinity symbol and the focus is still the same for the Live View contrast AF and for the optical viewfinder's phase detect AF. I guess that means that even though 125 yards isn't infinite distance for the lens at full telephoto it still is close enough for the microadjustment to be the same.

Don

Canon EOS 7D
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