If available, try to use the 6T with a fixed focal length lens. I would expect much better results. I sometimes used the 6T many years ago with the Nikkor 1.8/105mm. This combination worked very well. Today I am using another achromatic lens (Pentax T132) to increase the maximum magnification of my 2.8/165mm lens from about 1:7.7 to 1:3.7. Again, the results are very good.