I am as big a fan of Canon’s lenses as anyone; I resisted the temptation to switch brands for years simply because they offer certain lenses that I can’t imagine not having. When it comes to the new RF 800mm f/5.6 L IS USM and RF 1200mm f/8 L IS USM lenses, however, you should really think twice before you buy them.

Canon’s newest lenses, the RF 800mm f/5.6 L IS USM and RF 1200mm f/8 L IS USM, continue to round out their RF line and push into new extremes. At $17,000 and $20,000, respectively, however, they are some of the most expensive consumer lenses ever created, and even professionals for whom such lenses are a daily need should think twice. There is more than the price that should give you pause, however. Before we jump in, though, let’s establish all the relevant prices.

Prices of Canon Lenses, Teleconverters, and Combinations Thereof

• Extender RF 2x: $599

• Canon RF 400mm f/2.8 L IS USM: $11,999

• Canon RF 600mm f/4 L IS USM: $12,999

• Canon RF 800mm f/5.6 L IS USM: $16,999

• Canon RF 1200mm f/8 L IS USM: $19,999

Similarities With Existing Lenses

Adding a 2x teleconverter to a lens doubles its focal length at the expense of reducing its maximum aperture by two stops. For example, a 100mm f/2.8 lens would become a 200mm f/5.6 lens with a 2x teleconverter attached. As such, you might notice that the new RF 800mm f/5.6L IS USM and RF 1200mm f/8L IS USM are, at least by the numbers, equivalent to 400mm f/2.8 and 600mm f/4 lenses with 2x teleconverters, respectively. The RF 400mm f/2.8 L IS USM and RF 600mm f/4 L IS USM already exist, as does the Extender RF 2x.

Of course, just because the numbers line up, that does not mean Canon simply plopped the 2x teleconverter inside the existing lenses and called it a day. Manufacturers optimize the designs of different focal lengths specifically to deal with their unique challenges and issues; otherwise, we would all be a lot more teleconverters and a lot fewer unique lenses. It is worth noting the following, however:

Weights of Canon Lenses, Teleconverters, and Combinations Thereof

Extender RF 2x: 12 oz / 340 g

No doubt, the combinations of the teleconverters and respective shorter focal lengths are quite close to those of the longer focal lengths, though not quite identical. 

Designs

There have been rumors that these lenses are nothing more than the 400mm f/2.8 and 600mm f/4 with 2x teleconverters dropped in. Let’s take a look.

RF 400mm f/2.8L IS USM Plus Extender RF 2x Versus RF 800mm f/5.6L IS USM

As you can see, the differences are near the mount. The 800mm f/5.6 has an extra group of normal elements that likely serve as the additional magnification. However, there is an additional super ultra low dispersion element in front of said group, likely meant to correct for chromatic aberration that typically increases with teleconverters. So, in fairness to Canon, the 800mm isn’t just a 400mm with a teleconverter slapped inside. Is it worth the steep price increase for the extra element(s), though? 

RF 600mm f/4L IS USM Plus Extender RF 2x Versus RF 1200mm f/8L IS USM

The story is similar here. The front design is identical. Nearer to the mount, we see a magnification group along with a super ultra low dispersion element likely designed to correct chromatic aberration from the additional magnification. So, again, this isn’t just the 600mm f/4 with an internal teleconverter, but is it worth an additional $6,000 over just using the 600mm with a teleconverter? Let’s take a look below. 

MTF Charts

This is what you should care about most. All the argument about design and weight is interesting, but at the end of the day, how good are the images from each lens and combination? Let’s take a look. 

RF 400mm f/2.8L IS USM Plus Extender RF 2x Versus RF 800mm f/5.6L IS USM

We can see that the 400mm and 2x extender offers almost identical contrast performance compared to the 800mm f/5.6. There is a slight dip of about .05 in the Meridional measurement toward the corners of the frame, but the difference is so slight, I have a hard time believing it would be noticeable to all but the most discerning eye and would likely be easily corrected in post. 

For the resolution measurements, the Sagittal orientation is functionally identical, save for a very slight dip near the extremes of the frame. There is a notable drop in the Meridional measurement, with a gap starting at the center of the frame and reaching a maximum differential of about .15 about 17 cm from the center. It is still quite strong performance, however, and pretty close to identical to the 800mm f/5.6 nearer to the center. 

Is the difference worth $4,401? That’s your call to make, but if it were me, based on just the MTF charts, the answer would be a hard no.

RF 600mm f/4L IS USM Plus Extender RF 2x Versus RF 1200mm f/8L IS USM

We can see that the 600mm and 2x extender offers almost identical contrast performance compared to the 1200mm f/8. There is a mild difference in Meridional line nearer to the corners, but the gap is never bigger than .03 and is unlikely to have any notable real-world impact. 

When it comes to resolution, there is a constant gap of about .02 in the Sagittal line until about 17 cm, where it widens to about .05 at the extremes. The Meridional line shows a somewhat wider gap of about .07 at 10 cm, which widens to a maximum of about .12 at the extremes. Both show impressive performance, nonetheless. 

So, I’ll ask again: is the difference worth $6,401? I don’t think so. 

Other Thoughts

Weather-sealing

It’s worth noting that all other things equal, a single lens likely offers better weather-sealing than a lens plus a teleconverter, simply as the former has one less seal and point of ingress to protect. That being said, all the optics in this comparison are some of Canon’s best, and I doubt weather-sealing is going to be a major issue in all but the most extreme circumstances, regardless of which setup you choose.

Autofocus

Traditionally, teleconverters cause a hit to autofocus performance, particularly with 2x extenders. That being said, teleconverters have come a long way, and the autofocus performance of the RF Extender 2x has generally been praised.

Increased Versatility

A 1200mm lens is a 1200mm lens. A 600mm lens with two teleconverters is a 600mm, 840mm, and 1200mm lens. Yes, of course, you can add teleconverters to the 1200mm lens to extend it, and it’ll probably perform better than stacking multiple equivalent teleconverters to the 600mm to push past 1200mm, but when was the last time you needed a 1680mm or 2400mm lens? Sure, they sound neat on paper, but their real-world applications are few and far between. A similar argument applies to the 800mm situation. 

What You Should Spend Your Money On Instead

If it were me, I would save the thousands of dollars and get the shorter focal lengths and teleconverters without hesitation. The increased versatility and significant savings outweigh the relatively small gains in contrast and resolution. You could get an EOS R3 with change to spare if you go with the 600mm combination instead of the 1200mm! 

In fact, I wouldn’t even get the RF lenses. I have been adapting the EF 400mm f/2.8L IS Mark I USM to my EOS R5 for years without complaint. Autofocus is flawless (even better than it was on my 1D X Mark II), and image quality is spectacular. Canon absolutely improved the image quality across versions of these lenses, but they started out so high that even my picky eye is perfectly happy with the Mark I. The real advantage you get as you move up to newer versions is weight savings. There is absolutely something to be said for that (lugging that thing around always makes me think twice), but I always think about the several thousands of dollars I saved, and then, I’m perfectly happy to deal with the bulk. 

Your Thoughts

What are your thoughts? Are the image quality gains worth the extra thousands of dollars for the 800mm and 1200mm lenses, or are you better kff saving your money and using a teleconverter?