2 ACCEPTED SOLUTIONS
The EF 70-300L is NOT compatible with Canon's teleconverters - they will physically not fit on this lens.
If you want to get an extended reach, then the RF100-500L is a brilliant choice for the R5 (at a cost), but if you want to stick with EF lenses, then I can recommend the 100-400MkII or the Sigma 150-600c lenses.
However, given that the R5 has 45MP, it might be worth keeping your EF 70-300L and simply crop - it IS an excellent lens!
To demonstrate the potential of a higher MP sensor with this lens, this is the 70-300L with the quite unforgiving Canon EOS 5DsR, which has the cancelled AA filter and at 52MP shows any flaw in the lens or its use. Of course, to post here, the images have had to be SERIOUSLY downgraded, but you should get the idea.
As taken:
After cropping:
@drodow wrote:"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."
As mentioned, the extender won't physically fit the EF 70-300mm L f/4-5.6 IS USM II, so IMO if you are going to spring for the EF 100-400mm L f/4.5-5.6 IS USM II, I would go for the RF 100-500mm L f/4.5-7.1 IS USM. I agree with Trevor that the EF 70-300L II is a great lens. I have used it on all of my bodies, from an XSi, through various Rebels to the 7D mark II, 5D mark IV and now the R5 and R6. You will get good resolution with it on the R5 so you can crop in, if need be. I also have the EF 100-400mm L II and a 1.4X extender. I really don't care for that combo as it just doesn't give me the res I want, plus you are giving up a stop at 400mm. Like you, I shoot birds, more times than not, tiny birds like warblers. The EF 100-400mm L II and ring adapter on the R5 works great and if I get close, cropping still leaves plenty of detail and I could get a 10" print when needed.
Although I like the EF 100-400mm L II, I still bought the RF 100-500mm L for the R5 and let the EF 100-400mm L II live on the 5D IV. I like the RF glass and although I can only see a slight improvement in IQ in the RF L over the EF L glass I own, there is more to it then that, like they are generally lighter, designed better (according to specs), and I like the redesigned hood of the RF 100-500 L, I know, small thing, but it is what it is. Although EF glass works fine on the R systems, I think the RF glass is the way to go if you can afford it, it just feels right.
Tufted Titmouse - R5 and RF 100-500 L at 35 feet.
Ruby-crowned Kinglet - R5 and RF 100-500 L at 40 feet. These birds are under 3" and a pain to shoot. They hardly ever sit still and rarely come out in the open.
Newton
