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Sigma 500mm F4 Sport + 1.4 x - Importance of Camera and Lens Calibration

sigma lens calibration
Last week we had a customer send us a Canon Eos 7D Mk2 + a recently purchased Sigma 500mm F4 sport and a 1.4 x matched converter. This lens was pretty much out of the box. As the number 1 Sigma calibration specialist in the UK we see a lot of 500mm lenses and even more of the 150-600mm. On average we calibrate 5-6 150-600mm lenses a week so we were not surprised....yet!
He was complaining of soft images. Understandably, the lens being new, having a camera and lens calibrated was not something he considered. Fear being that the lens was faulty and wanted us cast an eye with a view to correcting this accordingly or sending back to the place of purchase with our reports.
The magnification factor of the 7D's crop factor along meant that the 500mm was the equivalent of an 800mm thus any micro adjustment would make a considerable improvement and with the 1.4 x converter the equivalent of 1120mm... again the minutest of adjustments making a considerable difference.
Having set up our workstation and run the appropriate tests the results are as follows:
sigma lens calibration
7D Mk 2 + Sigma 500mm F4 = -14 (the lens was back focusing considerably
sigma lens calibration
7D Mk 2 + 500mm F4 + 1.4 x converter = +2
The calculated Auto Focus Micro adjustment for the 500mm + 1.4 x may be considered acceptable (remembering that Sigma's tolerances are typically + or - 15 micro adjustments). However we are actually looking at a + 16 as it is counteracting the -14 already required to correct the 500mm on its own.
This goes to prove what we see on a regular basis that more often than not converters tend to add greater discrepancies with regards front and back focus issues. if any users have any concerns with regards the performance of their lenses why not let us have a look.