1. teleconverter
Logically, it is a teleconverter and I have the opportunity to extend the telephoto effect on each of my lenses by a factor of 1.4. This task is performed, the converter with the moderate factor of 1.4 as expected. I use the converter in this function, for example, at the Canon EOS 550D with a Tamron 70-300 VC and am very happy with the results.
In addition, there are two other functions, one of which was the following buying decision for me.
2. Adapter (APS-C lens >>> FF camera)
The teleconverter expands the image circle on by a factor of 1.4. This means that even the small image circle of a lens, which was built for APS-C sensors is expanded accordingly and the lens is at its full frame sensor (conditionally) use. For this purpose, the converter should ideally have a factor of 1.6 for use on Canon systems. Therefore, it may depending on the lens come to vignetting (or you can take the same one teleconverter with a factor of 2.0). The original EF-S lenses from Canon are built so expansive on the back that they can not be connected to this converter. This was so well described in the product description. But I own lenses from Tokina (11-16 and 50-135) and Tamron (17-50 and 18-250), which can be connected. In addition, these foreign manufacturers are working with a slightly larger image circle, because the same lens design should work for Nikon camera connections (1.5 crop factor).
This application is interesting for those who want to buy after switching from a camera with crop sensor for full-frame sensor immediately all new or lenses can. And exactly this application has moved me to buy a teleconverter. In particular, my Tokina 11-16 I want to temporarily continue using the new Canon EOS 6D. And it works.
3. Dust protection for the camera body
When I connect the converter to the camera body, then the light well is sealed. Most telephoto zoom and all super-zoom lenses pumps in back and forth back a considerable amount of air through the cell holder. The patch prevents this teleconverter laden dust draft. It is indeed not a priority function, but it is a nice side effect.
Originally, the title should be "more than just a teleconverter". However, the areas of application described here apply eventually for each teleconverter which is placed between the camera and lens. In fact, it is the low influence on the imaging quality of the lens used, which makes this converter so recommended.
