Hi John,
Nice article on crop vs. full frame, and use of Teleconverters. It prompted me to try to figure out if there was a similarly speedy way to go from crop <--> FF on a SONY A7R4. After a hundred more readings of the SONY manual (the manual is dreadful), I realized that it is simple to assign a "Custom Key" to that function (I chose C3). Wow! I can just press C3 and it instantly goes from Crop <--> Full frame. Increases flexibility when birds get really close and start to overfill the crop mode with a big telephoto.
Many thanks.
Great photos.
Harvey

The R5 and 600mm f/4 continue to amaze me. I am easily shooting better photos than I did with the 1DX Mark III. The autofocus is better, especially the eye focus that the DSLRs lacked, and the electronic shutter at 20 shots per second is helpful for the quick little head turns feeder birds do and the fact that it is silent. No longer is the sound of my camera making birds react that eliminates my chances to photograph them. I now have mostly mirrorless lenses but continue to use the $100 adapter to use my Canon 65mm macro, 180mm macro, and the 600mm. I know the RF 600mm is on its way and so it the R3, but don't know when I can get my hands on them. A year ago I was mildly interested in mirrorless, mostly from a teaching perspective, but now I am convinced mirrorless is here and switching helps me shoot the images I seek a lot. I realize it cost $$$$$ to switch, but I see no point in denying the mirrorless advantages. Heck, I don't even have to AF microadjust the R5, like I had to with all my other DSLR. For 45 years I shot macro, landscapes, and wildlife all over the world and never did I think new camera gear would help me out so much, but it has happened.