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. 

[JEJE12]

Alternatively and since I do not have unlimited budget, I was planning on using my RF 70-200 F 2.8 with an R7.. Hoping I could shoot most of the subjects within 70-200 range and use the R7 crop function for more reach if needed. Am I wrong to think it could be an alternative? Obviously not as good as the prime lens but still a good option.. no? 

[deebatman316]

@JEJE12 the EOS R7 doesn’t offer a crop function like Full Frame bodies. The EOS R7 is a crop and has a 1.6x crop factor. So there is no need for a crop mode for APS-C lenses.

[SignifDigits]

I am personally hoping for a R7 Mark ii or R10 Mark ii (if they add IBIS) in Spring 2026 to pair with my 70-200 f/2.8.  It will still be f/2.8 on an APS-C and have effective range of 1.6x the 70-200.  So, it sounds like a reasonable budget option to me as that's what I'm doing myself.  I hoping for enough pixels on the sensor and frames per second performance to fast storage to photograph the birds nearby with reasonable sharpness and detail.

[March411]

I can only answer your question from my perspective JEJE12. The bare minimum I would go if I was taking a trip to Kenya would be a 400mm. Even that may not give you the range/distance you need for some of the wildlife that is out some distance. But I have been know to spend more then I should sometimes, not smart.

That being said, the the RF70-200mm on the R7 would give you an effective equivalent focal length of approximately 112mm to 320mm. Additionally the EF400 on the R7 600mm. 

I have used my RF100-400mm quite a bit for wildlife but I had the ability to get closer because the animals were not dangerous.

Bottom line, if the funds are not available you are making a smart decision by not over spending. Use what you own, enjoy the trip, don't put your self in a bad position financially and you will get some great shots with the RF 70-200  f2.8 with an R7. Some shots, maybe not but you can live with whatever decision you make knowing you were smart.