I was looking into extenders(Teleconverter) for Canon lenses, and they are quite expensive at around $450 for the 1.4x III or 2x III. I know that extension tubes are a different story, and since they contain no optics the brand really doesn't matter. But what about for extenders? Do third party options exist and are they worth looking into?
Related: Are there any downsides in using 2x extenders?Are there any downsides in using 2x extenders?