Hey friend,
I have looked everywhetre in Sing but no shop has stock and nobody knows where to get except order from overseas.
SO I have made my own coupling lens with the 2 set-ups.
1) Koboron 70-300mm ( D=67mm) with 50mm (D=49mm).
2) Tamron LD IF AF 200-400mm with Sigma EX 28mm, both with D=77mm
I found out that it would be easier to view the subject with a teleconverter attach to the primary lens.
AF is useless, MF is only applicable when you push your lens to the magnifying range distance. Revice physics and you will understand how the thigs work as well as the calculation for the magnifying part.
Because I dun have extension cord for flash gun, I have to shoot under sunlight. DOF is really critical and hard to obtain sharp image since my lens were really heavy.