Recoverery of far distant (TNO) minor planet 1999 DE9 was detected this month at it's brightest at 20.3 magnitude. It was recovered after a series of tests to perform observed magnitudes:
See
www.astroshack.net/eamonn.php
Thses objects are more difficult to detect than asteroids because of their faintness. Other factors like the slow movement requires time duration of over an hour before you can see a shift in the image. You have to take 3 images to make sure of a real recovery. So in total it takes over 3 hours to detect one of these minor planets beyond the Solar System.
Eamonn A
  