I used the "ol string focus technique" which works like this. You set the camera up and critical focus the 8x10 on a subject. You then attach a string to the camera and stretch it to the point of focus. Then mark the point on the string. I use a small clamp.
Now you know that the lens is focused at a point that is at the exact distance as the string.
Once you close the lens and load the film holder you can easily check critical focus one last time before firing the lens. In theory it works perfect, your mileage may vary.
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