RF teleconverter and EF adapter madness?

[Kit Lens Jockey]

The talk of imminent RF teleconverters being released got me thinking. Thinking of something stupid and probably not practical or optically possible, but thinking nonetheless...

What would happen if one were to put an RF teleconverter on an RF camera, put an RF to EF adapter on that, and then put an EF lens on that? Could I finally turn my EF 85mm f1.2 into the 119mm f1.7 lens I have always dreamed of? Or maybe a 170 f2.4?

What about turning a 24-70 f2.8 into a 33.6-98 f4?

Or, for the ultimate exercise in pointlessness, making an 11-24 f4 into a 22-48 f8?

These are the hard-hitting questions we need answers to as we wait for the R5 announcement.

 

[AlanF]

That's relatively sane. Even more pointless is that I have a Kenco 3xTC, which I could put on an RF 2xTC, add my 2xTC and turn my 100-400mm II into a 1200-4800mm.

 

[Kit Lens Jockey]

Ok full disclosure I did try this one time with my 85 f1.2, a 1.4x teleconverter, and extension tubes, and unfortunately the lens couldn't really focus on much of anything because I had to put so much of an extension between the teleconverter and the lens to make it so that the converter didn't smash into the back of the lens. Would it be different if converting between an RF camera and an EF lens? Does it matter if the mirror box space that the lens is designed for comes before or after a teleconverter?

 

[AlanF]

Ok full disclosure I did try this one time with my 85 f1.2, a 1.4x teleconverter, and extension tubes, and unfortunately the lens couldn't really focus on much of anything because I had to put so much of an extension between the teleconverter and the lens to make it so that the converter didn't smash into the back of the lens. Would it be different if converting between an RF camera and an EF lens? Does it matter if the mirror box space that the lens is designed for comes before or after a teleconverter?

It was claimed a few years ago that you could stack a 1.4 and 2xTCIII with a 25mm tube in between. I evetually wasted money on a tube and later couldn't get it to AF with LV on 5DIV.

 

[Optics Patent]

For a big white EF on RF it gives appealing benefits to combine adapter and TC. No reason not to offer “long” TC units for EF on RF.

 

[Pape]

That's relatively sane. Even more pointless is that I have a Kenco 3xTC, which I could put on an RF 2xTC, add my 2xTC and turn my 100-400mm II into a 1200-4800mm.

could be good macro setup can shoot fly 1meter away

 

[Antono Refa]

What would happen if one were to put an RF teleconverter on an RF camera, put an RF to EF adapter on that, and then put an EF lens on that? Could I finally turn my EF 85mm f1.2 into the 119mm f1.7 lens I have always dreamed of? Or maybe a 170 f2.4?

The adapter is an extension tube compensating for the flange distance difference. You'll be able to focus closer, but lose the ability to focus to infinity.