I just purchased this teleconverter to go with my Sigma 50-500 F4-6.3 APO Lens and just wanted to leave some opinion for anyone else that might be considering. I'm satisfied with the 50-500 lens although I expected sharper images. I have seen images from the same camera and lens that look much sharper than I have been able to achieve.
As far as the converter, I was aware that I would lose 2 full stops but I was expecting that to apply to the 4-6.3 range however it applies to the 6.3. The aperture is F11 regardless of your zoom. I can go with larger F Numbers (ie. 12 13,etc.). I found that anything other than very bright direct sunlight leaves you with no choice but to increase the ISO, usually to 400 or higher.
Im sure the converter would be more suitable for a faster lens but if you plan on using it with the 50-500, plan on shooting brightly lit subjects only.
Just thought I would pass this on. Hope it helps someone.
Noted, thanks for that. I have the Sigma lens but had not given any thought so far to adding a x2.
Richard
I purchased the Sigma 100-300 f/4 + 2x converter last month and it works great . With the converter it becomes a 200-600 f/8 manual focus only but not a problem. At 600mm with the converter attached it is a little softer but you would never know once you add some sharpening in photoshop. You must have it on a solid mount or good beanbag to avoid shake.
The only thing with this converter it's the EX version it will not work with my Canon lenses due to the protruding front ellement so beware.
Terry