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Canon EOS RP manual says that the EF - EOS R adapter should be attached to the lens first, and only then should the entire assembly be attached to the camera.

I have understood that the same is true for teleconverters as well: the teleconverter should be attached to the lens first, and after it, the assembly should be attached to the camera.

However, especially with the EF - EOS R adapter, if having lots of EF lenses, it may be more convenient to swap just the EF lens, not touching the adapter that is left semi-permanently connected to the body.

If I understand correctly, a powered-on camera may become confused if the adapter/teleconverter is on the camera and just the lens is changed.

If I turn off the camera for the duration of the lens change and keep the adapter on the camera body, changing only the lens, can there be any bad effects?

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Canon designed the firmware that's running the camera, so if they say an order of operation for something, it's probably best to follow it.

That being said, I'd imagine this particular order is due to the camera wanting to communicate with the lens, and if no communication occurs or that communication is disrupted, then an error is thrown until communication is reestablished. It's possible that one must "reboot" the camera in order to get it to attempt to communicate again, even after lens reattachment (As Canon recommends for recovery on the 5Dmk2 [I can't imagine it's much different for other bodies]).

At best, removing the lens from an extension tube, TC, or adapter and replacing with another will have no effect.

At worst, your camera will throw an error forcing a quick reboot. I can't say that I've really experienced this with my extension tubes (I don't have a TC or adapter), but I'm also in the nasty habit of powering down on lens changes (yes, it's an old habit but it's basically second nature for me at this point).

Structurally, there's nothing different about the attachment order of operations. If using heavy lenses, maintain support of the lens and not the body (which you'd be doing anyway).

  • so... what's the recommended attachment order if I want to use a 400mm lens with 2x teleconverter, plus extension tubes so I can focus close, using an EOS-R adapter on a RF body? =P – scottbb Jul 3 '19 at 20:05
  • Wouldn't it be a good idea to always turn off the camera when changing lens anyway? I saw somewhere that it would reduce the chance of dust getting "magnetically" pulled in. – Fábio Dias Jul 3 '19 at 21:46
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    @FábioDias I've heard the same but never seen any evidence for it. At this point I'm chalking it up to a theory that spread like wildfire. Dust is a fact of life; so are sensor cleanings. At the end of the day, I don't think a hot swap is going to drastically change the need to clean the sensor anyways after a given amount of time. – Hueco Jul 3 '19 at 22:44
  • @scottbb I need to make a friend at a rental shop simply so I can try that out. I wonder what the magnification would be with, hmmm, 40mm of ET? – Hueco Jul 4 '19 at 12:51
  • You just nerd sniped me. I calculate that a Canon EF 400mm f/2.8L IS II USM, with a max magnification of 0.17, with 2x teleconverter has a max mag of 0.41 (assuming true ƒ=400 and true 2x). With 40mm extension the max mag goes to 0.46, and the minimum focus distance is reduced by 8 inches. Now if I can just remember what I was doing before I sidetracked myself with lens maths... =) – scottbb Jul 4 '19 at 14:07
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Today I wanted to test what will happen if I turn the camera off, and change the lens without removing the adapter from the camera.

After turning the camera back on, it just works perfectly with the newly attached lens. So I don't really understand why I should follow Canon's cumbersome advice.

Note this test didn't involve changing the adapted EF lens while the camera is powered on. It may work or it may confuse the camera; I don't know.

Nevertheless, it's easier to turn the camera off for the duration of the lens change than it's to remove the adapter while changing the lens.

Canon, by the way, advises you to set the camera's power switch to OFF while changing a lens.

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