>>4515756The problem is even if the better one costs double of that the Sigma still costs too much for such a poor image quality. It is effectively a 400 or 450mm on the long end considering how usable it is, after that you get strong blurring. And don't get me started on the bokeh quality, anything with branches or grass in the background just looks super busy with the hard bokeh. Even Tamron managed to bring down the hardness in the backgorund falloff and first party lenses not just give you the juicy sharpness but the pleasant bokeh as well. You can be sure your shots will be nice.
>>4515760Third party are a hit and miss with the EF-RF converter, I know Sigma had some trouble with rapid focus instability on the Sigma 150-600, instead locking on, the focus would jump back and forth behind and front of the subject making it unusable.
Like I said above, you are already dishing out a good amount of money, just get the first party lens, it can play well with the 1.4x first party teleconverter. Also you can be certain Canon makes sure their flagship EF 100-400 II plays well with the RF adapter. This is a lens you buy for long time use.
