Originally posted by Canada_Rockies I used an M 28/3.5 reversed to help a friend with a jewelry problem. A "jeweller" had badly scratched her wedding ring and she took him to court with help from an 8x10 inch print. The 28 reversed has a little over 2x on 35 mm film. She showed the print in court and the 'jeweller' caved. Best beer I ever earned.
The 28mm f3.5 has a very good reputation for macro work when reversed, better than any of the higher speed, more expensive 28mm lenses made by Pentax. And to comment on a point made just above. When using a lens of wide to short telephoto focal length (about 90~100mm or shorter) for macro work at a reproduction ratio around 1:3 and higher it is always necessary to move the camera to focus rather than using the focusing ring. At magnifications of life size and greater, it's impossible* to focus using the focusing ring. The old rule is: at reproduction ratios above 1/4 life size, use the focusing ring to change /increase the ratio/magnification, move the entire camera+lens to achieve focus.
* If you want to think about why:
With a unit focusing lens (not internal focus) the distance the lens must be from the focal plane to achieve focus is determined by the distance between the front of the lens and the subject, As the reproduction ratio gets closer to 1:1 if you use the focus ring to move the lens further from the focal plane you simultaneously move the lens significantly closer to the subject which would require moving the lens yet further from the focal plane which would move the lens yet closer to the subject. etc. Focusing using the focus ring is not possible because of this loop that develops as you approach a life-size close-up.