R5/EF Adapter compatibility

[drodow]

Hello, I have the EOS R5 with a Canon Mount EF Adapter and a 70-300mm 5.6L IS USM lens. I need to know it the Canon 1.4x extender will work with this configuration?  I hope so otherwise I will have to sell the 300 and buy the 100-400.
Thank you for your help.

[FloridaDrafter]

---

@Tronhard wrote: 

"So, as I see it the risk is very much the individual's decision. Certainly, in the context of the original question, I think it would be very unwise to suggest an undocumented and unapproved means of adding an extender to a person seeking advice.  I accept the fact that John sought to provide some context, but I am dubious of the validity of the sources he quotes to justify the measure - to me what the manufacturer recommends should be the bottom line."

---

I don't think anyone is suggesting using this combo, at least that wasn't my takeaway, but the OP specifically asked about this configuration. After Johns post, I just thought it was interesting and posted my results. I tried the link John posted, but the link on that page to the "report" about the EF 70-300mmL now being included was dead. I got a "Page Not Found" error or something similar. As for possible damage to the lens or extender, I can see that happening. The RF 100-500L limits zoom as well when paired with the RF 1.4X, I think it stops at 300mm (420mm), I'm not sure it's for the same reason, but it's a limitation when using the RF extender and the RF 100-500L. Does it bump the rear element or has Canon added some sort of stop or cushion? I just don't know.

Newton

[Tronhard]

As you say "I don't think anyone is suggesting using this combo" but as John stated - on two occasions:
1.  "If you are willing to accept essentially a fixed 420mm lens then it will work."  and...
2.  'the 70-300 L's rear element retracts into the lens far enough that, at about 250mm, there is enough clearance for Canon extenders to mount.'... My solution to the damage risk issue was to Gaffer Tape the lens zoom ring to lock it at the 300mm mark while using extenders."

It is clear to me that we are talking about an unofficial and unsupported work-around to get an extender to mount onto the lens for which it is not designed, and is not supported by Canon - can you image them saying put gaffer tape on a lens as a safety feature?  I certainly would not suggest it as a solution to put forward to a third party who has come to the site looking for quality advice, but that is MY personal position.

In the end the fact that the extender can be made to fit is not really here or there.  While it can be made to fit, the question is SHOULD it be made to fit when it was not intended to, and should we be suggesting it on a site provided by Canon, and on which we are guests with privileges?

The difference between this and the RF 100-500 is that Canon clearly states that the extender is intended to be used with the lens, and the limitations thereof.  As I understand it, there is a lock that prohibits the mounting of the extender on the lens or the reduction of focal length while in use, thus safeguarding the integrity of the optics. 

[FloridaDrafter]

---

@Tronhard wrote:

"It is clear to me that we are talking about an unofficial and unsupported work-around to get an extender to mount onto the lens, and is not supported by Canon - can you image them saying put gaffer tape on a lens as a safety feature?"

---

LOLOLOL, you're killing me over here, brother! I was taking a sip of Drambuie right when I read that last statement and coughed it up my nose. I imagined tech support saying that.

BTW, Drambuie is better sipped than sniffed 🙂

Newton

[Tronhard]

😂 
In one of my careers, I worked on a support team back in the day, and if you knew some of the ideas that came up as they tried to brainstorm a solution under pressure...
The Drambuie sound good... sadly, I'm stuck at home right now with a pinched nerve in my back, trying to take photos of birds out my window in the hope of not going stark, staring, bonkers. 😝

[Waddizzle]

Good.  I am late to the thread, but it is good to see two solutions.  

Here is another one, for future reference.  Download a PDF copy of full instruction manual, and search for the phrase “lens group”.