Will a TC affect the aperture? So I have a Canon R10 and I don’t have the funds to buy RF lenses so I shop for EF lenses. I already know that the R10 will apply a 1.6x factor to the focal length. I’m looking into saving up and buying a 400 or 500mm lens for wildlife. So question #1 is, If I put the Canon 400mm f/4 on my Canon R10 will it be a 640mm f/4 or 640mm f/6.4? Questio…