RF 100-400 for birds and other stuff, my take

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BirdShooter7 Veteran Member • Posts: 7,161
RF 100-400 for birds and other stuff, my take

When Canon announced the RF 100-500L and the 600mm and 800mm f/11 lenses I was pretty shocked. My many years of using SLR’s suggested that such “slow” lenses wouldn’t provide a very good user experience. It wasn’t until I got to use the R5 & R6 that I started to realize just how much potential lenses like these actually have. In fact, I eventually bought the RF 800mm f/11 lens because I found it’s light weight and solid optical quality to be so useful to me.

American Alligator (All images in this post should have EXIF intact)

My photography is heavily focused on birds and I make my living doing bird photography all over the world. My primary lens is the EF 500mm f/4. I use both the original IS USM version and the mk2 and I use both lenses often with EF 1.4x TC’s. My current primary camera is the R6 and occasionally the R5. I find the 500mm f/4’s to be great tools capable of providing great results in a wide variety of situations.

Fiddler Crabs on Parade

However, I do encounter situations where 500mm is simply too much focal length so I typically like to have a long zoom lens handy. For example, I might encounter an interesting insect or reptile or maybe even a landscape that are better suited to a shorter lens. Since I’m already packing a big heavy 500mm prime, lighter weight and compact size are very desirable. The RF 100-400 is so light that I can throw it in my day pack and really don’t even notice that it’s there.

Nelson’s Sparrow

Another quality I really want in a secondary telephoto lens is the ability to focus close since the big primes don’t usually have terribly close minimum focus distance or terribly high max magnification. There have been so many times that I have encountered a beautiful moth or butterfly or an interesting reptile or amphibian or cool orchid… and haven’t been able to really do the subject justice because I didn’t have a suitable lens handy. I also sometimes encounter mammals that are just too big to photograph with a 500mm lens and end up with nothing but head shots, so the ability to zoom out is quite nice to have.

Forster’s Tern

White Ibis

Over the years I have tried a bunch of different lenses to go along side my big prime and haven’t really been thrilled with any of them for a variety of reasons. The 70-300 mm options have been limiting because they often don’t give as much focal length or magnification as I really want. Also the lighter and smaller options typically fall a bit short in terms of image quality. The ones with the best image quality are typically fairly heavy.

The 100-400 mm options have typically been a better fit for me in terms of focal length but again the best performers are pretty heavy. I loved the EF 100-400mm L mk2 but it was just too heavy for me as a secondary lens. Up until now I have been using the Sigma 100-400mm C lens which has been a good compromise. It’s relatively small and light, AF performance is satisfactory and the image quality might not be class leading but it is very solid and the max magnification is pretty good.

Yellow-crowned Night Heron

When the RF 100-400mm f/5.6-8 IS USM was announced I figured it could very well be a great secondary lens for me. The Canon lens is over a pound lighter than the Sigma. The difference is even bigger if you consider that you don’t need the EF to RF adapter. The Canon lens is also slightly more compact, though that difference doesn’t jump out at you nearly the way the weight difference does. The difference in minimum focus distance is pretty significant with the Sigma coming it at 1.6m and the Canon at 0.88m. The max magnification is also noticeably better on the Canon lens; 0.41x vs 0.26x.

What do you give up by going from the Sigma to the Canon? Probably the most obvious thing is that the Sigma lens has a faster aperture. At 400mm the Sigma is f/6.3 vs f/8 for the Canon so 2/3 of a stop which can be pretty significant. However, I find I often use the Sigma at f/8 and f/11 anyway to try to get a bit more DOF due to the nature of most of the photography I do with the lens. So for me, I think I can live with the limited aperture given the substantial weight savings.

American Avocet

American Avocet

The Sigma does come with a lens hood included while the Canon doesn’t. I find it annoying that Canon doesn’t include a hood for a lens like this but it’s been a long-standing policy with Canon so no surprises there. Neither lens has a tripod foot but I think this is more of an issue for the Sigma than the Canon because of the weight difference. The Sigma also retails for $799 vs $649 for the Canon. I personally don’t use a hood with either lens just to keep things as light and compact as possible.

One of the things that I immediately noticed when I started using the RF 100-400 was how fast and “sure footed” the AF is on the R6. Focus speed is in my opinion excellent and the Canon lens does seem to be less jittery and more “sticky” than the Sigma lens. I found that the Sigma 100-400 has a lot more tendency to lock onto the subject quickly then drift off than the RF 100-400.

Pied-billed Grebe

I was really pleased with the R6’s ability to achieve focus with the RF 100-400 in dimly-lit situations. I could often achieve focus on my subjects in light that was so low that I couldn’t get acceptable shutter speeds without going way up the ISO range or even maxing it out.

Snowy Egret

The RF 100-400, possibly due to its narrow aperture at 400mm, seems to have a lot less of an issue getting “stuck” when the focus is on the background and the subject is close than lenses like my EF 500mm f/4’s. With the 500mm lenses I often have to turn the manual focus ring to bring the focus closer so the AF can catch the subject. With the RF 100-400 I can usually get the focus on the subject in situations like this by simply pumping the AF-on button once or twice, which I find to be much quicker.

Seaside Sparrow

Another area where I’m impressed with the new RF 100-400 is with the image stabilization. I’m finding that it is noticeably better than that of the Sigma. I was able to get shots at 400mm and 1/30s without too much trouble where I was really struggling to get usable shots with the Sigma at the same speed.

From my initial outings with the lens I am finding the in the center of the frame the image quality at 400mm and f/8 (wide open) is pretty good and I don’t think I’ll have any problems being happy with the results. Out at the edges and corners of the frame I am seeing some softening of the image which is a little disappointing but really not unexpected, especially considering the price of the lens.


Possibly the thing I love most about the AF on the R6 is the ability to focus pretty much anywhere in the frame which lets me use all of the pixels the camera offers instead of having to put the subject towards the center of the frame and then crop for composition afterwards like I usually did with my SLR’s. I’m getting the feeling that with this lens I might need to be careful just how far off-center I can put my subject and still be happy with the resulting sharpness.


One of the things I have noticed about the RF 100-400’s optical rendering is that I sometimes notice a bit of a glow in high contrast transitions from in focus to out of focus areas. If you look at the edges of the petals as they go out of focus you can see what I’m talking about. It’s probably not something that would be a big deal when viewing the whole photo but it wasn’t something I particularly liked. It kind of reminds me of what the old EF 70-300mm DO lens used to do in similar situations.

The bokeh from this lens is in general not one of its strong points in my opinion. It probably has a lot to do with the narrow max aperture so shouldn’t be of much surprise but I do notice a lot more “busy” bokeh than what I’m used to.


Like every piece of photography gear, the RF 100-400 has its compromises. You get a quick-focusing, sharp lens in a compact and light-weight package at a budget price. You give up some edge & corner sharpness, great bokeh and a fast aperture in exchange. I’m finding this lens to be a good set of compromises for me. It’s basically looking like a great lens that I never knew I wanted until I tried it. I’ll definitely be bringing this one along with me on future trips.

Clapper Rail

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Some of my bird photos can be viewed here: https://www.flickr.com/photos/gregsbirds/

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