Completely agree. Could you add a bit of detail about your holders and the maximum apertures you typically use with them? I have crappy holders and usually stick to f16 and f32 for 4x5 and 8x10, respectively, which is sufficient for film plane slop. I can open up another stop if I'm careful and lucky but due to the scanner limitations and corner aberrations I don't benefit from going wider if my objective is a uniformly high resolution image.
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