why micro focus adjustment ?

Started Feb 25, 2013 | Questions thread
Allan Olesen Veteran Member • Posts: 3,391
Re: You asked, I believe...

JerryCurtis wrote:

I know this doesn't sound logical. but it's my experience.

If the AF sensor is misaligned, it will actually have the largest impact on the focus error when short focal lengths are used. So to me it does sound logical.

You can test this by playing with a calculation tool for macro spacer rings. If you insert a 1 mm spacer ring behind a 50 mm lens, the focus distance changes much more than if you insert a 1 mm spacer ring behind a 200 mm lens.

Of course the shallower DOF of the 200 mm might more easily reveal the focus error, even it is smaller.

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