Focusing screen not square (450d/XSi)

Started May 21, 2013 | Discussions thread
TTMartin Veteran Member • Posts: 7,304
Re: Focusing screen not square (450d/XSi)

photonius wrote:

TTMartin wrote:

Tilting a mirror does not rotate the image.

Actually, yes, it can, if the mirror is not exactly lined up with respect to the relevant axes, the image can appear rotated.

I was wrong about that.

So if the main mirror were misaligned it could also cause the image on the focus screen to appear rotated.

But, the alignment of the penta mirrors wouldn't matter as the relationship between the focus squares and the lens image is set at the focus screen. Any later rotation would affect both the image and the focus squares the same.

Thanks for the correction.

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