The pics in the zip file attached is my enlarger. Can anyone explain what the black bellow is for, because my prints are generally always in focus when the bellows are contracted, not expanded. Does the picture degrade or improve the further the lens moves away from the negative? Is there a "good practice" element to follow? http://www.tedsmithphotography.com/temp/enlarger.zip Also, note the negative carrier. This one is rubbish and partially broke - where can I get a replacement and what sort should I get?