EF 400mm F 2,8 L II USM vs RF version for Canon R5 and R6

[JEJE12]

Hello

I am am amateur wildlife photographer and I was wondering if anyone has experience using the EF 400 2.8  L II USM with the R5 and or R6. Obviously I would prefer to buy the RF version of that lens but it is simply too expensive for me. I could also rent it when I go on trips but I figured that if I go to Africa once a year and Montana a couple of times a year, I could probably buy a used EF 400 2. 8 instead. I own the RF 200-800, RF 70-200 2.8 and 100-500 F4 but the RF 400 2.8 is spectacular and was wondering if perhaps the EF could get me excellent result for a fraction of the cost.. any insight would be greatly appreciated. 

[SignifDigits]

I do not have experience with that lens, so I will only comment on what I know that might be useful to you.

Having purchased some EF lenses for my R6 Mark II I will tell you a few things you are giving up, and you can decide how important they are to you.  I'm sure this is due to the 8-pin communication of the EF lenses vs the 12-pin communication of the RF lenses.

First, you cannot expect the manual zoom ring to give you the zoomed in closeup with the "Lens Electronic MF" set to "One Shot --> Enabled (Magnify)".  If you are used to using this on your RF lenses (and I really enjoy that capability myself on my RF 200-800 f/6.3-9 IS USM) based upon my experience with the EF 70-200 L f/2.8 iii IS USM and the EF 100mm L f/2.8 IS USM you are giving that up.  I bought both of those lenses (one used one Canon refurbished) for less than the price of the RF 70-200mm f/2.8 l IS USM Z.  No regrets on my part, though if I were a professional I would have the Z in my bag instead.

I find that using manual focus while autofocus is on for those lenses causes some internal pushback against the autofocus system (see below - even trying this looks like it could damage that lens).  Again, likely due to a lack of the communication between the lens and the camera that the RF affords.  It also makes some noise, which could be a consideration in the field for wildlife (and based upon the information at the bottom here seems like it is a feature we should disable for these EF lenses - I'm trusting DeeBatman316 will correct me or affirm this at some point).

The AF for is generally accepted as a bit faster on the RF lenses.  The EF version AF is fast enough for me, but the AF on my first AF camera - the Minolta 7000 was fast enough for me as well, so take that for what it's worth.

The image quality is generally considered to be improved on the RF lenses over the EF lenses, though the EF 100mm version is considered to be a bit better for astrophotography by some.

The version of the lens that you are looking at as far as I can tell is not listed as currently supported on the Canon support list at https://canon.jp/support/repair/period.  The supported version is EF400 2.8L IS III USM.  So that is a consideration for you, as well.

I expect that you can take some wonderful pictures with the EF lens that you are considering - many professionals have proven that is the case.  If you've found the RF 200-800 low-light performance inadequate at 400mm and the downsides vs. cost savings equation is worth it to you to get that low-light performance at 400mm, then hopefully you will enjoy the lens.  But only you can make that personal happiness decision in the equation.

Again, I am sorry that I cannot offer the direct comparisons for you, but hopefully this more peripheral information will be useful to you.  Thanks for dropping in and participating.  Please keep us in the loop and let us know what you decide.  I'm including the following from the excelled DeeBatman316's knowledge base that applies also (slightly shortened a bit to remove things that I think are not applicable to your lens):

Note lenses with an electronic focus will only allow Full Time Manual Focus with the camera set to One Shot AF. If set to any other focus mode the electronic focus ring is IGNORED. The EF 300mm F/2.8L USM lens was the first lens to feature an electronic focus ring. It is also Canon's first Ring Type USM lens. If Manual Focus Override isn't working check and ensure USM Lens Electronic MF / Lens Electronic MF is enabled. On the EOS M & EOS R series it is DISABLED by default and must be enabled for Electronic MF to work. The AF/MF switch physically disengages the AF motor from the lens' focusing elements. NEVER attempt turning the focus ring on a lens with Micro Motor without switching the lens to MF first. The same applies to Micro USM lenses too these lenses don't support manual focus override.  Nano USM lenses may look similar to Micro USM lens but the lens itself will say "Nano USM". They also don't spin the focus ring when the AF motor is active.

[jrhoffman75]

The EF 400mm f/2.8L II lens was highly rated for image quality, but it is heavy (about 2 pounds heavier than the RF lens). Plus the additional weight of the RF-EF adapter.

The RF 100-500 at 400mm is close in image quality

https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=741&Camera=979&Sample=0...

If low light is a consideration none of the lenses will match f/2.8 at 400mm.

Given the ~$14K cost of the RF lens I think the EF would be an excellent choice if f/2.8 is a need.

[deebatman316]

@SignifDigits what you’re feeling when the camera is driving the lens’ AF motor and you turning the focus ring at the same time is. The clutch under the focus ring ensuring that you don’t damage the lens. That clutch is designed to slip against the Ring Type USM AF motor. For lenses that have a mechanically connected focus ring. EF lenses with an electronic focus ring do work with Full Time Manual Focus. Lens Electronic MF" set to "One Shot --> Enabled (Magnify)". It doesn’t work with lenses without an electronic focus ring. This is because the lens doesn’t send the signal to magnify the image when the focus ring is turned. Since power isn’t needed to manually focus the lens. RF lenses support this because most lenses use Nano USM instead of Ring Type USM. Though some lenses still use Ring Type USM such as the RF 85mm F/1.2L USM lens. Due to the large lens elements. But it retains the electronic focus ring design as its older EF Mount counterpart. So the clutch is working as designed to prevent damage to the lens. I wouldn’t advise turning the focus ring when the camera is driving the AF motor. I would also turn off Continuous/ Preview AF. The camera will be constantly trying to focus. If you ever need to override focus for some reason you can’t. The clutch will simply slip and allow the AF motor to drive the lens instead. In this case the camera wins and you can’t override focus manually. So you can keep USM Lens Electronic MF / Lens Electronic MF enabled for lenses with focus by wire. But the Magnify option is not available with lenses with a mechanical focus ring. The EF 400 2.8L IS III USM lens is focus by wire. The last generation Telephoto and Super Telephoto lens went back to focus by wire.

[SignifDigits]

@deebatman36 - thanks for the details.  I'm glad to know I didn't and cannot damage the lenses and am happy to let the lens win with those settings.  I can always put the switch on manual and override if I wish to do so.

I'm also happy to hear some EF (those with electronic focus rings) do support the feature so I don't hand out any misinformation.  I just know for certain "Lens Electronic MF" set to "One Shot --> Enabled (Magnify)" doesn't work those two EF lenses that I have, and wanted the OP to know that it might work.

It appears that the also the following two lenses are also focus by wire with an electronic focus ring and should work for not on the latest version that you mention but also these (which include the interest of the OP, I believe):

• EF 400mm f/2.8 L USM
• EF 400mm f/2.8 L II USM

[deebatman316]

@SignifDigits yes both of those lenses are focus by wire. The 1st generation IS telephoto and super telephoto lenses versions dropped focus by wire. The only Ring Type USM lens that kept the design was the EF 85mm F/1.2L II USM lens. It was based on the original version which was based off of the EF 50mm F/1.0L USM lens. Which was also a focus by wire lens. Now older EF lenses without USM AF motors released between 1987-July 1990. Used Arc Form Drive (AFD) AF Motors. These lenses too also have a clutch. But it’s not used for manual focus override. Instead when the lens is set to AF it completely disengages the focus ring. From the lenses focusing elements. You can turn the focus ring all you want but it won’t actually change the focus. It will turn indefinitely and these lenses are easy to identify compared to Micro Motor lenses. These lenses include a focus distance window. Also the focus ring doesn’t turn when the AF motor is active. Also when the lens is set to MF it disengages the AF motor from the lens’ focusing elements. Then connects the focus ring directly to the focusing elements. Basically in this case it’s a one way clutch. It can only accept focus adjustments from either or. Also the AF and Aperture control works sequentially when the camera is set to Servo AF. Meaning these lenses are only capable of 3-4 FPS. These lens AF & stop down sequentially and not at the same time. Micro Motor solved these issues when they released in August 1990. USM lenses never had this limitation. Also Canon released a few L lenses with this AF Motor before USM became more common. Also no L series ever used Micro Motor or Micro USM only AFD or Ring Type USM. Once Ring Type USM became more common all EF L lenses used them from then on.

[March411]

JEJE12, Happy New Year, I hope your flip to 2026 was excellent!

The short answer is yes the lens will perform well on both of those R series bodies. I no longer own the the EF 400 f2.8 but I can tell you that it is fully compatible with the Canon R series bodies when used with a the Canon EF/RF adapter. The AF performed better on my R5 and R6 MkII bodies than on my 5D Mk IV and the images it produced were stellar, it was traded when I picked up my RF100-500. 

The link below is good one to hold onto when wanting to check various Canon EF lenses compatibility with the R system. It will let you know areas that with the EF/RF adapter some functions could be limited.

Supplemental Information Compatibility 

[JEJE12]

Thank you. I am heading to Kenya in June and going on night safari.. I was hoping I could get nicer photos with it with low light... 

[SignifDigits]

I apologize if I sounded too negative and for providing potentially erroneous information earlier.  You will be getting a new super fantastic lens - woohoo for you!  Please share some photos before and after Kenya - and above all, be safe.

[March411]

You will be able to extend your shooting later into the evening with the f2.8 lens and get some nice bokeh in your shots.

If it's in the budget and in good condition it will be worth picking up. I also check on end of service and Canon has the EF400 2.8L IS III USM noted as Undecided which is also positive. JEJE12, just make sure you are purchasing it from a reliable source and in good condition, it would be a drag if you picked it up and it had challenges. 

Good luck and it would be great to see some of your images when you get back from Kenya.