I belong to a local camera club. We have something like 1500 members and we have regular events where any number of us could show up. That is how I ended up at the hot air balloon events in February.
A while ago, we had a lens calibration event. Since I had no clue what this really entailed, I thought I should go.
To begin with, a lens depth of field (DoF) varies with the distance to the subject and the f-stop settings. Let's assume the DoF, given a distance of 10'and an f-stop of 2.8, is supposed to be 12" for this specific lens. That means that 4" should be in focus IN FRONT of the focusing point and 8" should be in focus BEHIND the focusing point. For some lenses, this is adjustable!
Below is the "before" photo where we did the baseline setting of the lens. Notice that on the middle scale to the right, you can see clearly up to almost the 20 mark. And, looking to the back, you can only see clearly to the 4. Since the point of focus is on the red "0", this is bad, bad, bad, bad, bad. Did I say, "bad?"
This explains why I was a bit surprised when I took the photo below. I fully expected the DoF would include more checkers in the back of the board. I thought I had another 1.5-2" of DoF that just wasn't there.
So, after carefully reading the manual, which states something like, "this is not for the faint of heart and you shouldn't do this at home without a trained professional", the lens was calibrated. The entire process for two lenses took about 15 minutes.
Notice the DoF in the photo below! Here you can see the 10 in the front is almost totally sharp and in focus. But, the 20 in the back is sharp and in focus, too.
Calibration is NOT that tricky. Using this device helped a lot. If I recall, this little set up costs about $300. But, the deal was to bring in two lenses and have them calibrated for $10. With the exception of that date with the McKenzie triplets, this was the best $10 I ever spent. But, that's a different story.
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