I ordered the Canon RF 100-400mm yesterday, it arrived this morning, and the lens now "Pre-order" status on the website. I had time for just a few tests and one or two shots only, so I'll give my initial impressions and follow up later with more. I do have the RF 100-500mm and an EF 100-400mm II (for a 5DSR), and they are my reference points.
The RF 100-400mm is just so light in comparison and in absolute terms. It weighs just 680g complete with hood, compared with 1700g for the 100-400mm II or 1610g for the 100-500mm. That kilo of weight, 2.2 lb, makes a huge difference. The little lens on the R5 is so comfortable to hold and so balanced when shooting, especially with the control ring towards the front, it is much easier for shooting and hiking with.
In terms of IQ with my standard charts at 20m, the bare lens is pretty close to the 100-400mm II at 400mm. With the RF 1.4x, it's not as sharp as the 100-400mm II at 560mm or the 100-500mm at 500mm. It's not nearly as good at 800mm as the EF lens with the 2xTCs or even remotely in the same league as the 100-500mm at 1000mm. It does focus noticeably closer than does the RF 100-500mm. The lens is probably best used without teleconverters.
It's not as good as my RF 100-500mm, but I can stroll around with it dangling from my hand rather than being a heavy item on a shoulder strap. It will be perfect for my wife who finds the white zoom lenses too heavy. And, it's also pretty inconspicuous when when walking around urban areas. So, it's a keeper for me, being good enough for much of my casual photography, and so easy to carry around or pack. It has the same nominal resolution on the R5 as the RX10 IV fully extended (f/4 220mm, 2.7 crop factor, 20 Mpx sensor) which I have liked
for casual convenience. But, the Canon is much sharper.
Here are my first two shots: a Great Tit flying off me feeder towards me, and a Stubble Rosegill mushroom.


The RF 100-400mm is just so light in comparison and in absolute terms. It weighs just 680g complete with hood, compared with 1700g for the 100-400mm II or 1610g for the 100-500mm. That kilo of weight, 2.2 lb, makes a huge difference. The little lens on the R5 is so comfortable to hold and so balanced when shooting, especially with the control ring towards the front, it is much easier for shooting and hiking with.
In terms of IQ with my standard charts at 20m, the bare lens is pretty close to the 100-400mm II at 400mm. With the RF 1.4x, it's not as sharp as the 100-400mm II at 560mm or the 100-500mm at 500mm. It's not nearly as good at 800mm as the EF lens with the 2xTCs or even remotely in the same league as the 100-500mm at 1000mm. It does focus noticeably closer than does the RF 100-500mm. The lens is probably best used without teleconverters.
It's not as good as my RF 100-500mm, but I can stroll around with it dangling from my hand rather than being a heavy item on a shoulder strap. It will be perfect for my wife who finds the white zoom lenses too heavy. And, it's also pretty inconspicuous when when walking around urban areas. So, it's a keeper for me, being good enough for much of my casual photography, and so easy to carry around or pack. It has the same nominal resolution on the R5 as the RX10 IV fully extended (f/4 220mm, 2.7 crop factor, 20 Mpx sensor) which I have liked
for casual convenience. But, the Canon is much sharper.
Here are my first two shots: a Great Tit flying off me feeder towards me, and a Stubble Rosegill mushroom.

