BTW I forgot to mention in my previous response that while you can of course use a Micro Nikkor 55mm f2.8 (which has great resolution and so should work very well), you do not have to use a micro/macro lens for bellows kit as the bellows provides the extension needed for close focus and magnification of the image. If you have one, an ordinary 50mm lens will usually suffice so long as it is good enough to provide the resolution needed - something like a 50mm f2 would probably be ideal in this respect. The lens should, in any event, be stopped down to f8 or f11 to provide depth of field (otherwise almost non-existent at these distances and hence prone to focusing error) and to ensure the image is as sharp as possible. (Slow shutter speeds are not really an issue as with a bellows and slide holder, the entire set up is locked to the front of the camera and any movement affects the whole system). Also, the user manual should give an indication of which lens this is calibrated for - if it's calibrated for a 50mm lens and you use a 55mm one, you should expect that there will be a slight cropping factor which may crop out some edge details of the slides - which may or may not matter. Having said all of the above the 55mm Nikkor Micro should in other respects work well.