</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Darkroom ChromaCrafts @ May 4 2003, 08:39 AM)</td></tr><tr><td id='QUOTE'>This may be a stupid answer and maybe at the enlargement percentages most of you are doing it doesn&#39;t make a difference, but with the extreme enlargements I do, I found that my focus would appear to be dead on, but the print would not be sharp.&nbsp; Well, I finally figured out that I was focussing on the print platform with complete disregard for the depth of the paper itself, causing me to be minimum of 2-4 mm out of focus. </td></tr></table><span class='postcolor'>

at an el-factor of 35x, DOF is on the paper side much much more than 4mm, even if we assume a circle of confusion below the resolution of our eyes. However, DOFocus, i.e. the tolerance of the negative, is always critical. I sometimes do 50x enlargements and never encountered a paper-side DOF problem, if the enlarger is well aligned. Lens performance might be another issue. Paper is UV sensitive and might see another picture as your eyes, if the lens has aberrations at these wavelengths.