Originally posted by reh321 TC's are always an adventure. When I thought I might be given a K-1, I got an AdaptAll TC for my AdaptAll 60-300mm, and suddenly I had purple fringing on a lens that had never provided any fringing before.
I have no lenses that have never caused purple fringing. What lens were you shooting with? TCs are for A*, FA* DA*, or high end DA lenses. Most of the time, it's the original lens that's the problem, not the TC. A TC will magnify PF that's already there. I have no knowledge of purple fringing with a TC on a lens that never had PF without the TC. But I've also only ever used Pentax TCs.
But I regularly shot with TCs either the HD DA 1.4 TC or the F 1.7x AF Adapter (and sometimes both TCs stacked) on my DA*200, DA*60-250, DFA 100 macro, Tamron 80 macro and Tamron 300 without issue. On my F 70-210, visible PF becomes worse. My solution, don't use a TC on the 70-210.
A good lens with a good TC isn't an adventure. Everything has to be top notch or all bets are off. After all a 1.7x TC magnifies the image 1.7 times. Any weakness in less than top notch lenses will be magnified 1.7 times.