Sigma 8mm with teleconverter for CFWA?

Hi!

I'm in the process of changing from a FF Canon SLR to a crop-sensor model. I want to keep using my existing Sigma 8mm lens for CFWA, but the circular frame of the lens still cuts across the corners of the APSC sensor. I wondered if anyone else has tried using this lens with a teleconverter for a more exaggerated perspective. I'm particularly wondering if the lens can still be used on autofocus when using a teleconverter as I've read some posts in regular photography forums that suggest it might be possible to use a 1.4 converter, but very little info has been given on the subject. I've tried searching Wetpixel but the results show posts containing any of the keywords, rather than all.

Many thanks!

For the sake of completeness, and in case anyone sees this post who might be interested, I took a punt and bought a Kenko 1.4 teleconverter (MC4 DGX model - the Pro-300 is apparently for use with lenses 100mm plus) and I'm pleased to report that it works with my Sigma 8mm! Really happy!