There are a few different types of slide duplicator designs:

• Some attach to the filter threads of a lens. This type of slide duplicator is easiest to use on crop-sensor bodies. Image quality depends mainly on the quality of the lens. Color quality depends on the light source.

  The duplicator is basically a slide attachment and a tube with a diopter filter inside. The macro filter may introduce some barrel distortion, which can be corrected in software. Any loss in image sharpness won't be significant as long as you are able to visualize and focus on the film grain.

  

  Use a zoom lens to find the appropriate focal length, then switch to a sharper prime, if you have one available. Use the minimum ISO available on your camera, and stop down to the sharpest aperture of your lens (usually F5.6 to F8). You don't have to worry too much about long exposure times since the attachment is motionless relative to the sensor. If your camera or lens has image stabilization, turn it off.

• Some attach directly to the camera. All necessary optics are built into the duplicator. Some allow zooming from 1x to 2.5x. You can zoom in on sub-miniature formats, but you won't be able to zoom out to capture entire 35mm frames on crop-sensor bodies. You can capture and stitch multiple sections of the film.

• Some are intended for use with bellows. Lens selection and bellows operation may require some trial and error. As the bellows is used to move the lens away from the sensor, sharpness is decreased and a "glow" may appear.

  

  You can use the thin lens formula to figure out approximate distances and focal lengths you'll need for a given reproduction ratio (magnification, m = v/u).

  1/u + 1/v = 1/f

  u = subject distance
  v = image distance
  f = focal length

  For 1:n, u = (n+1)f, v = (n+1)f/n. So for a 50mm lens with a reproduction ratio of 1:1.5, u = 83mm and v = 125mm.