C70 Speedbooster for EF glass. Does this mean RF glass has smaller image circle? How does this all work?

[Mt Spokane Photography]

When the lens is attached to a FF sensor, it will have the best peak sharpness, lowest pixel density, no additional optics.

But compared to using a FF lens with a simple adapter on a crop sensor, a Speed Booster might be better, because it is not punching on the image.

Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.

 

[dcm]

I suspect that's for lens support. Smallrig sells something similar to but the weight of the lens+rigging on the cage instead of the RF mount.

That was my first thought since the EF-EFM adapter has a detachable lens support. I found it strange that there was no mention or attachment included. Always interesting when there is a visible feature that is ignored. It's like having an extra, undocumented button on a camera.

 

[Joules]

Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.

The point was that aspects like poor resolution or CA are usually more prominent on APS-C Tham FF because of the greater magnification. So by compressing the image circle those are also reduced. So it becomes a question of how much aberration is added through the speedbooster vs. how much the lenses own aberrations are hidden.

If the lens already outperforms the crop sensor or the speedbooster isn't all that great optically a bare lens will of course perform better.

 

[padam]

Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.

Again, it depends on what you are comparing and I explained the specific case where adding this adapter will lead to sharper results with potentially slightly less chromatic aberrations than without it. Will the flare become worse with the extra elements? Will the bokeh rendering change? Possible.
There are quite a few comparisons regarding the Metabones Speed Booster which you can look up if you want.
With the Canon adapter there are no side-by-side examples as of yet, but on the first look video, it looks to be even a bit better than the Metabones (maybe because it is even more optmised for the Canon sensor size)