I am in the process of moving to mirrorless (R6) and have a Canon EF 70-300mm f4-5.6 IS USM. Am not sure whether to invest in a Canon RF 100-500mm F4.5-7.1L IS USM or whether I can still use my current 70-300mm? Can I use a mount adapter plus an RF 2 x extender and if so what performance will I get? Any advice/thoughts?
i use 2x extenders myself occasionally and to be honest they are best on faster zoom lenses with a constant aperture, or primes, you may be able to use them effectively in bright light situations like a sunny day or on planets and the moon for that reason if you have the option to go for a lens that has the focal you want vs a shorter one and a x2 then i'd go for the longer one, then have the x2 as an :added option" rather than using it for the main reach you will also be using an RF lens designed to work on an RF body, another + as of yet i havent moved to RF mount, i may go for the R7 as a second body but it won't be until the price has dropped or we see if this is a tester lens for canon on crop and they come out with a higher performance R crop i've been on M50 for 2 1/2 years and i'm still very happy with it, well i have two now for events, one thing RF cant do for me is compact. my current long lenses are 100-400mm c and 150-600mm c sigmas, the quality of 400mm x2 is less than 600mm on its own i do use the x2 with the 150-600mm for bright objects like the moon and planets or when i have plenty of light. i have also used the x2 with primes and constant ƒ stop zooms and they can handle the light drop pretty well sorry i can't help you with a direct RF comparison
I would grab myself a Canon EF to R adaptor, put it on the front of your R6, and throw your 70-300mm on, and give it a go. If you find that the 300mm end of your current lens is not long enough, or you find other things that you don't like, then look at upgrading in the future. I have a R mount body, but I only own EF glass. I have found that I can use my 400mm f5.6 L lens with a 1.4 extender, and it works fine. Ok, the AF is a little slower, but even without the extender, the camera I own is not a speed demon. Gary
