Some time ago I mentioned on the "Think Camera" website the difficulty of getting a lens reverser to fit the front of my Tamron 28-300 mm lens and allow me to use a Pentax or Praktica lens reversed on the front. One of the members suggested that I could make one quite easily by using 2 cokin units glued together back to back. I did this and found it to be very useful because it eliminated any problems of binding when trying to unscrew the fitting.
I had been using my Minolta 80 px ring flash for some time on my 90mm Tamron macro lens and the thought occurred to me that it might be possible to use it on my reversing lens as well.
Unfortunately the Pentax and Praktica lenses that I had been using were too large for the ring flash to fit.
I then thought of the Takumar lens on my old Heiland Pentax. The Honeywell H2 model had the early lens that did not have the automatic re-opening mechanism and was therefore smaller in circumference. It also meant that the light button on the ring flash could be used to easily find the subject if pics were being taken with the camera hand held rather than tripod mounted. Set on the front of my Tamron 28-300 mm lens it can give an enlargement of approx. 5x life-size.