Originally posted by Oggy Hi John
Not sure if it helps but I have a Tamron 1.4 TC with the same part number.
It does give AF function, both on screwdriver and SDM, but the focus reliability and IQ are compromised.
I tend to get a better picture with a crop.
I have not had a problem with the Tamron and any of my screw drive F2.8 lenses. I have used it extensively for surf photos paired with an FA* 300 F2.8 lens and I have done some sever crops on the resulting images and still had very nice results.
using SDM motors... this TC struggles to lock focus with my 200mm F2.8 but it seems OK with my 50-135
There is a common misconception that teleconverters always have a significant (negative) impact on resulting images. These shots are taken with STACKED teleconverters. This is 300mm F2.8 + 2x +1.4x (Canon mind you) for an equivalent of 840mm F8. I took the resulting image and cropped about 1/3 of the total pixels in both cases to get this