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Try the dot tune method for AF calibration. It's very fast and easy.
50X the focal length in mm, so 1750mm. 1750mm=68.89 inches. So set up a high contrast AF target in line with the focal plane approx. 68 inches from the camera. Doesn't need to be 68.89, could be 65, or 70. Just get it close to that.
Take the camera and place it in live view mode. Use the 10X magnifying setting and auto focus on the target. Verify that it is a sharp capture. Turn off the live view and then turn the focus mode to MANUAL, while not bumping the focus ring. Now you're ready to begin narrowing down the AF tune range. You're going to pick a number, either + or -, doesn't matter. All you're doing is looking for the range of numbers that give you a verifiable focus confirmation. Hold the AF button on and look in the view finder for the green light to light up. Keep doing this, both plus and minus, until you find the number where you do NOT get an AF confirmation. So say you get one at +16 and not one at +17, then +16 is the end of the tune range on the positive side. Continue this for the negative side as well.
Then you calculate the midpoint of those two numbers. So if your camera tells you -8 and +17 are the two ends of the spectrum, you select an AF tune value in the middle of that, so +4.5. Since there's no +4.5, you pick either +4 or +5.
There's a video on youtube, as well as a well laid out thread on this forum. This is the method I use to AF tune my lenses.
Another way to check the AF of that lens is to focus it in LV at 10X magnification and check the results against regular AF through the VF.
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