Focusing screen not square (450d/XSi)

Started May 21, 2013 | Discussions thread
photonius Veteran Member • Posts: 6,816
Re: Focusing screen not square (450d/XSi)

TTMartin wrote:

mfait wrote:

AnthonyL wrote:

From time to time I've tried to use the focus points to try and align vertical and/or horizontal lines for instance of buildings, only to get home and find I'm having to rotate the image to get it square.

Today I belatedly tried a couple of tests using the frames of the lounge window.  In this picture the centre focus was directly on the vertical/horizontal intersection, the vertical points on the vertical bar and the horizontal points on the horizontal bar.  Handheld but that isn't the problem (I'm still fairly steady ).

A similar test using the grid lines on live view is satisfactory.

I reckon the image is about 2.15deg out.  Are there any easy solutions?

You don't actually see through the focusing screen.  The focusing screen is under the mirror.  The focus points are for display purposes in the viewfinder so you know where they are located.


Therefore, either you mirror or your pentamirror is a bit off tilting the image in the viewfinder.

You don't see through the focusing screen, but, you do see the image projected ON the focusing screen.

On the 450d/XSi focus squares are etched on the focus screen.

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.

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