Step 1: Material
-Reflex body cap (for my Nikon D40 the BF-1A) 5 euro
-Magnification lens (diameter 10cm, focus about 280mm) 5 euro
-PVC pipe reduction D=10cm to 5cm 2 euro
-PVC pipe D=10cm 1 euro
-PVC maintenance joint for 10cm pipes 9 euro
-Self adhesive black velvet (and optional black rugged self-adhesive)
I also used a saw, a drill and a threader and screwdriver.
Step 2: Drill the body cap
I had no bigger than 10mm drill tips, the hole should be bigger to avoid vignetting(dark in the corners)
Step 3: Cut the maintainance joint - put the lens in place
put the lens in place and with the help of a flashlight(the plastic is a little transparent) find the exact place for the screws to hold the lens in position. Then drill holes and thread them.
Add a little of self-adhesive velvet to hold the lens and avoid little movements and noises.
Add velvet also around the tighter part of the maintenance joint to have no leak and make the sliding movement softer.
Step 4: Assemble all parts
Put the maintenance tighter section in the regular pipe.
Put the wider reduction section in the wider section regular pipe.
Cut the excess of the wider section of the regular pipe.(then fix with glue the reduction-pipe connection)