If you’re in need of a versatile telephoto zoom lens, there aren’t many choices for the RF mount. Unless you use the EF-RF adapter, there are only two options available, the RF 100-500mm or the RF 100-400mm. Is the much cheaper RF 100-400mm a wise choice?

Have you made the switch to the Canon DSLR to the Canon mirrorless system? In that case, you probably have a selection of EF lenses available, perhaps lenses made by other manufacturers like Sigma or Tamron. It is no problem using these lenses with the EF-RF adapter on Canon mirrorless cameras.

If you want to skip the EF-RF adapter, you’re forced to buy Canon lenses. After all, other manufacturers are not allowed to produce RF lenses with autofocus as of this writing. So, if you like to use a telephoto zoom lens like a 100-400mm, the available options are limited, to say the least.

The Canon RF 100-500mm f4.5-7.1L IS USM is an amazing lens. It’s large, heavy, and very expensive. If you can spare the money, I would recommend the lens without a doubt. That said, I can also imagine this isn’t a lens that everyone can afford. So, you need an alternative.

There isn't much choice for Canon EOS R camera users when it comes down to a zoom lens in the range of 100-400mm, unless you use an EF-RF adapter.

Fortunately, Canon released the RF100-400mm f/5.6-8 IS USM. It’s a lens that is much smaller, lightweight, and much, much cheaper. You can easily buy four of these lenses for the price of a single RF 100-500mm lens.

The RF 100-400mm next to the RF100-500mm L lens. Which one would to prefer to carry with you on a hike?

If a lens is that much cheaper compared to its bigger brother, how well does it perform? Since it’s not an L lens, you might expect its performance to be not as good. Still, it needs to be a good lens because Canon can’t afford it to be only a mediocre lens. Canon Netherlands provided me with the RF 100-400mm f/5.6-8 IS USM for review. 

The RF 100-400mm f/5.6-8 IS USM is a small lens, only 16.5 centimeters long. Its weight is 635 grams, which makes it easy to take with you. The lens does extend when zooming to 400mm. It will increase in length by 7.6 centimeters. Because the weight is kept mainly near the camera, it won’t be too off-balance when zoomed in. The lens doesn’t have a tripod collar available, something to keep in mind if you’re using the lens on a tripod.

The RF 100-400mm has a good build quality, although it falls short on the L lens quality, of course.

The zoom ring is wide and rotates smoothly. It increases in diameter towards the front end of the lens, which makes it easy to find without looking. The focus ring is placed in front of the zoom ring and has a finer texture. Lastly, the control ring is placed at the front of the lens barrel.

There are three switches available. The locking switch will lock the zoom mechanism at 100mm focal length, preventing any unwanted extending of the lens barrel. The other switches offer the ability to deactivate the image stabilization or the autofocus. There is no focus limiter or different stabilization setting available.

The AF/MF switch and the stabilizer switch. There isn't much more to be found on this lens.

The lock switch will lock the zooming mechanism at 100mm.

The lens is made from a good quality plastic and feels quite robust. It lacks weather-sealing, which is a pity. Because it’s not an L lens, there is also no lens hood or pouch in the box.

The image stabilization is rated up to 5.5 stops. This can make a lot of difference for using a lens with a focal length in this range. Theoretically, the image stabilization will allow you to shoot at a shutter speed of 1/15 s, assuming the subject will allow this.

Combining the RF 100-400mm lens with a camera that has in-body image stabilization, the rating will increase only by half a stop towards six stops, which is not that much.

Such a small size and lightweight lens comes at the cost of a small maximum aperture.

The maximum aperture of the lens ranges from f/5.6 to f/8. This may sound not ideal, but if you compare the values with the RF 100-500mm lens, it isn’t that big of a difference. Still, you might need to bump up the ISO if a faster shutter speed is important. If that isn’t the case, you can rely on the image stabilization.

The small maximum aperture makes the use of high ISO values more common if a fast shutter speed is important.

One of the biggest benefits of this lens is its size and weight. It makes it easy to take the lens with you. Just put it in your bag or on to your camera and go out. The focal range makes it a versatile lens for a lot of different kinds of photography.

If you love to photograph animals, it’s an ideal lens. I noticed how the minimum focus distance of 88 centimeters at 400mm works perfectly for semi-macro. It allows a maximum magnification of 0.41x, ideal for flowers and insects, among other small things.

Just take the lens with you. The weight and size makes it easy. The focal length is ideal for bird photography and many other kinds of subjects (EOS R5 + RF 100-400mm at 400mm, ISO 800, f/11, 1/125 s).

EOS R5 + RF 100-400mm at 400mm, ISO 100, f/8, 1/250 s

EOS R5 + RF 100-400mm at 400mm, ISO 200, f/11, 1/160 s

It’s wise to keep an eye on the shutter speed, though. Especially when there is not much light available, it’s easy to rely too much on the image stabilization. It might be necessary to use a high ISO setting for this lens on a regular basis. Since most EOS R cameras perform reasonably well at high ISO levels, this should not be a problem.

Semi-macro is possible thanks to the minimum focal distance of only 88 centimeters (EOS R5 + RF 100-400mm at 400mm, ISO 800, f/8, 1/640 s).

This small flower is only two centimeters in size. (EOS R5 + RF 100-400mm at 400mm, ISO 100, f/8, 1/800 s)

Being such a cheap lens, especially compared to its bigger brother, the RF100-500mm L lens, I was surprised how good the images looked. There are some pincushion effects at 400mm, and the vignetting is close to two stops at the corners. 

There is a bit of pincushion distortion at 100mm focal length and some vignetting, but nothing shocking. The lens correction is turned off for this example.

At 400mm, the pincushion effect is barely visible, just like vignetting. The lens correction is turned off for this example.

Since most people will have the automatic lens correction activated in camera, most lens defects will be corrected. The real-life results will look good, and they're perhaps even close to the quality you find with the RF 100-500mm L lens. Only if you compare it side by side in a controlled situation might the quality difference become more apparent. But who does that in real life?

Although the RF 100-500mm L lens can be used with a teleconverter, it’s not truly built for that purpose. The focal range will be limited a lot, making it only possible to zoom at the longer end. On the other hand, the RF 100-400mm is fully compatible with both the 1.4x and 2.0x teleconverters. This increases the focal length range to 160-640mm or 200-800mm, depending on which teleconverter you choose.

Unlike the limited zoom range of the RF 100-500mm with a teleconverter, the RF 100-400mm can zoom over the complete range with use of the teleconverters.

The downside is the reduced maximum aperture you end up with. If f/5.6-8 bothers you, the f/8-f/11 with the 1.4x teleconverter or f/11-f/16 with the 2x teleconverter definitely will. If you don’t mind the smaller aperture, you need to realize there is also the diffraction problem with these small apertures, especially with high-resolution cameras like the Canon EOS R5.

If you are in need of these long focal lengths, maybe the RF 600mm f/11 or RF 800mm f/11 lens may be an alternative, or you can choose for one of the two mirrorless APS-C cameras Canon has released. Using the RF 100-400mm on these bodies will provide a nice increase in magnification without the problem of an even smaller aperture.

Although the image quality is less compared to the more expensive RF 100-500mm L lens, the difference is not that much. Perhaps if you compare the images side by side, it will be visible. There is also the longer zoom range in the more expensive of the two, of course, and the wider maximum aperture. Then again, the difference is only marginal.

A side by side comparison

The RF 100-500mm L lens has a better build, weather-sealing, and the tripod collar. This can make a difference when using the lens in challenging weather conditions. Also, the speed of the autofocus, in combination with the focus limiter and different image stabilization options, will make the RF 100-500mm L lens a good choice for many that need a lot of control. But it is quite an expensive lens, beyond reach of many photographic enthusiasts.

Not only in size, but there is also a big difference in weight. The RF 100-400mm is less than half the weight of the RF 100-500mm.

With the price in mind, the RF100-400mm f/5.6-8 IS USM is probably the better choice for many. The image quality is very good. It won’t match the bigger brother, but it comes close. Lastly, the weight and size of the RF 100-400mm makes it a great lens to have and to take with you.

EOS R5 with RF 100-400mm at 225mm, ISO 1,000, f/11, 1/160 s

There aren’t any alternatives available as of this moment. If you’re okay with using an adapter, any lens with an EF mount can be used. In that case, any EF lens with an adapter is still a good option, with lots of lenses to choose from. Still, I can recommend the RF 100-400mm f/5.6-8 IS USM, because it is a really nice lens for an affordable price.

Nando Harmsen is a Dutch photographer that is specialized in wedding and landscape photography. With his roots in the analog photo age he gained an extensive knowledge about photography techniques and equipment, and shares this through his personal blog and many workshops.