Re: Sigma USB Dock calibration data of 35mm and 5Diii.
I just spent a few hours characterizing my new Sigma 35mm using Dot Tune on a Canon 5DM3.
First a word about Dot Tune. I am extremely impressed with this method. I think of it as a stud finder. You find the left edge of the stud and then the right. You set your value right in the middle. If one edge is off the scale then you use your knowledge of the width to find the middle. I did all testing by listening to the beep alone (Beep Tune anyone?). I set 15 consistent and immediate beeps as my threshold for a valid sample. Any delay or missed beep was a disqualifier.
I tested 6 distances. I ran the test 3 times for each distance. The width in every case was either 14 or 15. The width was so consistent, in fact, that I would be confident finding only the left edge and adding half the width for center in the future.
The edges were always within one count of each other for each distance. This level of repeatability certainly inspires confidence. Once tuned for a distance I checked AF against live view focus and found the results to be spot on.
Side notes: I found my testing results to be insensitive to target pattern. I used the modelling lamps from two Elinchrom strobes for consistent illumination throughout. I found the results to be VERY sensitive to focus distance. I used a Bosch laser distance measuring device to confirm all distances. All distances are from camera focal plane.
12.25\" +4
14.75\" +6
26.25\" +17
69.00\" +15 (50x FL)
138.0\" +11 (100x FL)
276.0\" 0 (200x FL)
infinity (need to wait for sunrise to do test outdoors)
I was not expecting these results (especially at the longer distances). In the coming days I plan to go back and fill in the intermediate distances so I can plot the lens performance over the entire focus distance range.
Jun 09, 2013 at 11:09 PM
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