No downside with the 1.4x TC other than losing 1 stop of light. To be able to extend my Z 100-400mm to 560mm, that’s a small price to pay. Auto focus speed and sharpness remain excellent.
works well but you loose a lot of light about 1 to 3 stops
Works well loose a little sharpness nothing bad. Adds 3 stops to my nikon 180-600 at 600 the lens is f6.3 and with the converter it is f9. So definitely should only be used outdoors or very bright lite areas