>In a previous article, mjzach@mmm.com (Mark Zach) says:
>>I am having trouble getting my semi-home made slide copying system
>>to work out. I am hoping someone has some input on what I should try >>next. The system is really pretty simple. I use a commercial >>extension bellows between my Nikon FG and a Nikon Series E 50mm lens. >>The bellows is mounted on a plate on which is also mounted a fixture >>that holds a slide. This was all put together very precisely, so
>>I'm sure that everything lines up.
>>The problem is that I cannot get the slide in sharp focus. There >>seems to be a rather large range where the focus is qualitatively
>>the same, but no point where the focus is really good.
>>The question is: What can I do to get a sharp focus? I suspect
>>that I need a different lens, (and I am certainly willing to buy one) >>but what exactly do I need?

The lens you are using is an excellent choice for this purpose.
In some ways (used in the normal orientation, and not turned
around) it works better than the 55mm Micro-Nikkor for slide
copying, though any lens would need to be stopped well down
to perform well with the curved slide (compromise focusing
between the edge and center of the slide helps). You may be
running into a common problem when near 1:1 focus: the situation
you described - and it is frustrating! I would suggest making
the bellows an arbitrary 2" long to start, then move the slide
to achieve focus (rather than trying to focus on the slide at
an arbitrary distance - which may not work). Once you have found
sharp focus, make small changes in the bellows length (followed
by moving the slide to focus) to make size changes.
Hope This Helps