Any ballpark ideas on what the exposure time would be? A purpose built ipad enlarger wouldn't need an adjustable column. Change what's on the screen if you want to crop. Say a Paterson 10x8 printing easel that slides in and out. No neg carrier but a paper carrier instead. With the right software, almost all parts of the image can have a separate user defined print density. Don't know the correct term is but section up the image like it's a 'painting by numbers' canvas. Assign a zone/density to each section and the software has the negative be the correct amount of blue and yellow in each section to give the result you wanted.