In a previous post I had some problems with focusing my 4x5 cambo when using 2:1 and beyound. The image was not sharp (wrong focus).

I now have a solution for this.

I made a piece of glass which fits in my 4x5 when the back is removed.

The thickness of the glass is made at 4.8mm (2 pieces of glass filled up at the sides until 4.8).
I measured the distance from a 4x5 fidelity cassette with a micrometer to film of 5mm, With film it is around 4.8mm. So my glass is now at the position where the film is located.

I now put on the normal back and focused the image (3:1).
I removed the back, added the plain glass and refocused with a 10x peak loupe at the air image which is very bright {I do not know the right english name} (NL: luchtbeeld). WOOOOOW! The distance between the focus back and this is 8mm more to the front.

I do have to print the neg, but it looks sharp to me.

Is there anyone who did notice the same?
I never had this problem when using 1:1.
Looks like focusing is becoming very specific beyond the 1:1 and that there is some mathematical error that is getting quadratic larger beyond this 1:1.

I do use a normal cambo back where the ground glass is a original cambo and it is positioned in the right way. Only at these micro enlargements I get these problems.