Testing the focus adjustment of a lens - home made style.

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lmow20
lmow20 New Member • Posts: 8
Testing the focus adjustment of a lens - home made style.

Hi all,

I am trying to establish if my lens is as sharp as it should be. It's a 400mm f5.6 USM from Canon, and it's on a 5D IV.

I have made a home made setup to test the focus accuracy. I can't decide whether the image is a sharp as it should be, and if the focus needs adjustment. Please comment even if you think I'm talking balderdash. Thanks. The Lego man was placed such that the front of his head was exactly parallel with the 10cm line on the clipboard.

There would be a 1/cos(A) x h, the height of the lego man error on this, but given the angle was about 10 degrees, and the lego man was only 4 cm tall, it comes to perhaps a mm max.

Questions:

is the image sharp? (i have nothing to compare it to)

is the AF spot on 10 or does it need a tweak?

Let me know what you think of my makeshift setup!

Canon EF 400mm f/5.6L USM Canon EOS 5D Mark IV
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