======SLR Piggyback mount======
I made my own piggyback mount using a telescope mount ring and an old tripod. I bought a spare mount ring off of Ebay for $16. The final tripod was about $30 when I bought it some years ago.

=====Attempt #1 (failed)=====
My first try was to use the head off of a tabletop tripod. It did not work as the head did not hold the camera securely enough.

This is the same mount ring as used to hold the telescope on the goto mount.



I drilled a hole in the center to mount the tripod head.



This is the tabletop tripod.



The head removed with one screw.



Here is the assembled mount.



=====Attempt #2 (success)=====
Attempt #2 involved a regular tripod head.

This is the same mount ring as used to hold the telescope on the goto mount.



The donor tripod.



The head removed.




All 3 pieces (the base of the head unscrews from the head. I had to cut the bottom part off the tripod.)



A little 2 part epoxy and the base for the head is now part of the mount.



Here is the whole thing assembled.