Teleconverters RF vs EF

Shawn1519 wrote:

Asking the question a different way, take any lens/teleconverter combo (staying with the same format of EF or RF), put an extension tube between the lens and the teleconverter, and how does that effect image quality? That is in effect what Canon did with their RF 600 F4 and RF 400 F2.8 lens by incorporating the RF to EF adapter into the lens.

The answer is badly. By how much depends.

That is not what canon did with those. The distance from the lens to the sensor is still exactly the same in the RF version than it was for the EF version. It is the same whether you used "EF + DSLR", or "EF + RF2EF + R-body" or "RF + R-body". That dimension is the critical one.

If you add TC to the mix, things change. The rear of the TC must be the correct distance from the sensor. That is again a constant. The distance itself is a matter of design - in that respect EF and RF TCs differ ... as does the one embedded in RF 800 and RF 1200 as it seems to be even further away from sensor than EF TC.

Now when you put the lens in front of the TC, the lens distance is no longer the one it expects. That difference is, however, built into the TC design. It corrects the distance difference created by its own length. No more and no less than that.

So if you use "EF + EF TC + DSLR", everything is fine. If you use "EF + EF TC + RF2EF + R-body" instead, everything is still fine. It is also just as well to use "EF + RF2EF + RF TC + R-body" ... as long as you can find a fitting adapter of correct length. It is even optically OK to use "EF + EF TC + RF2EF + RF TC + R-body". The distances play still correctly as both TC:s correct the distance difference caused by their own length.

However, if you put extra extension somewhere in between, things are no longer going to play nice. The strength of the effect likely depends on how much you add compared to how much distance there is supposed to be from the last element to the sensor. That's why it is really bad idea to put extra extension on body side of TC:S ... and particularly RF TC:s.

But one strange anomaly still exists (and this was pointed out by one person in this thread). By design, a RF tele won't fit on a EF2RF adapter. But yet the RF 600F4 and RF 400F2.8 lenses violate this design by allowing a RF tele to fit on the back of the (built in) EF2RF adapters on those 2 lenses. This tells us that Canon modified the EF2RF adapter that they welded onto the RF 600F4 and RF 400F2.8 lenses.

don’t understand what this means.

I think your original questions show correct understanding, but I am not sure your conclusion is correct. Look into extension rings

The reason the RF2EF adapter does not fit in front of the RF TC:s is not optical. It is mechanical interference between the extruding part of the TC and the light baffles in the adapter. The adapter needs the baffles in order to eliminate unwanted reflections with ALL the EF lenses. There are some sad examples with third party adapters on why that matters. I'd never use my modified adapter without TC - that would be asking for trouble.

When they made the tele lenses, they didn't have to worry about how reflections on any other lens work - they just had to avoid reflections on THAT lens. That they have been doing for decades. Sometimes there are baffles, sometimes not. They also have more freedom to design the potential baffles as the TC in those lenses seems to be yet another design and even further away from the sensor than the EF extenders are.

[It appears Steve already wrote most of this, but I missed it.]

Just imagine, if an RF2EF adapter becomes available that fits onto the RFx2 extender, it would be possible to mount :

RFx2 + RF2EF + EFx1.4 III + EFx2 II + 100-400 IS L II

giving zoomed at 400mm a 3584mm equivalent on an R7 !  You could shoot the man in the moon with that.  Will have to see if the AF tracking locks onto him if he's running around fast.
Ok, shooting at f/32 might be challenging, and a very stable tripod will be needed!
Sharpness?  We'll worry about that later

For a couple of dollars/pounds/euros more, an EF 600mm f/4 will even bump that up to 5376mm and gain a stop.

Magnifying all the aberrations from EF 2x II 5.6 times...

I am not sure if eye AF works also with the helmets of the astronauts!

Shawn1519 wrote:

Franz Kerschbaum wrote:

I am not sure if eye AF works also with the helmets of the astronauts!

sounds like Canon needs to get busy with updating their focus tracking to include astronaut helmets - maybe they can add it to part of human eye tracking.

Shawn

He doesn't appear to be wearing a helmet this evening !
Anyone else spot him too?
(ok, I might have highlighted his eyebrow a little, top right)

R7 + RF2EF + Kenko 1.4x + EF 1.4x III + EF 2x II + EF 100-400 II resized to 50%