For a long time in the history of photographic gear, with a few exceptions (e.g. mirror optics), lenses were designed to have a maximum aperture of f5.6 or faster. When autofocus came along, this stricture was especially important because early AF systems could not auto focus with slower lenses. However, as AF technology improved a few lenses started appearing with a maximum aperture of f6.3.
Throughout all this, Canon in particular held steadfastly to the f5.6 restriction. And then, mirrorless happened. Once Canon entered the mirrorless fray, they blasted through the f5.6 barrier with gusto, by-passing f6.3 with hardly a glance. The initial rumors of this change of direction predicted an RF 100-500 f4.5-7.1L IS USM zoom, a lens somewhat similar in concept and use to their EF 100-400 f4.5-5.6L IS USM. The relative pros and cons of these two zooms were discussed in the abstract here.
Then came the official announcement on July 9. Not only was the RF zoom a reality, but two inexpensive long primes debuted as well -- at f11! Now that the RF 100-500 is officially announced it’s time to update our initial comparison to the EF 100-400. Afterward, we'll briefly discuss the surprising and unusual 600mm f11 and 800mm f11 lenses.
How Do the Specs Stack Up?
A number of questions were posed before firm specifications for the zoom became available. How does the image quality at the long end compare to the EF 100-400 with 1.4X extender? What is the aperture of the RF lens at 400mm compared to the EF lens? What was the weight and size of the new RF lens? How much would the RF lens cost? There were also questions about AF performance, and while those await testing of a production lens sample, the other questions now have answers. As a reminder, the discussion primarily centered around using each lens on the RF-mount system, the only fair comparison given that RF lenses cannot be adapted to EF-mount cameras.
First, the price of the RF 100-500 is now known. Clearly it is more expensive at $2699 compared to $2199 for the EF 100-400. But, if one adds a 1.4X extender at $429 and an RF-EF adapter for $99, the EF cost tops out at $2727, a smidge higher. Add another $100 if one wants the control ring adapter to bring the EF combination up to full equivalency with the RF lens. Of course, many people may already have the EF 100-400, and possibly a 1.4X extender as well, in which case the EF combination is limited only to the cost of whichever adapter one chooses.
Which brings us to image quality, surely an important concern in any decision. The bottom line from examination of Canon Japan’s MTFs is that at 100mm the RF is better than the EF 100-400, at least in the central area of the image circle -- albeit by only a small, and probably insignificant, margin. At 500mm the RF MTF curve is lower than the EF lens at 400mm, but this isn’t the relevant comparison. What most want to know is how each performs at its maxumum 500/560mm focal length.
Once again, based on Canon Japan’s MTF charts the RF MTF at 500mm is better than the EF lens with 1.4X extender at 560mm. While the focal lengths are not equal, they do represent the longest focal lengths available for each lens. And, although these MTFs are theoretical (as are most manufacturer published MTFs), they should represent a fair relative basis for comparison within Canon’s own line. While actual tests will be needed to confirm the performance suggested by the MTF curves, the RF lens appears to be a small, and once again probably insignificant bit better optically. It is helpful that use of the RF is not inconvenienced by the need to install and remove an extender to take advantage of the full focal length range.
In the case that one already has an EF 100-400 lens it might be just as well to stand pat – especially if, as the MTF charts suggest, there are only modest differences in image quality.
Regarding maximum aperture of the RF lens at 400mm, initial information is that if exposure adjustment is in 1/3 stops then the max aperture at 400mm is f6.3, but if exposure adjustments are set to 1/2 stop steps the max aperture is f5.6. Since nothing about the lens optics are changed by the arbitrary reporting choice of exposure adjustments increments, this is probably more of a numerical display artifact rather than a real difference. Additionally, an independent test by a respected reviewer found that the RF lens switches from a reported max aperture of f5.6 to f6.3 at 363mm -- which it holds until 472mm. To us, this seems a fair compromise, especially since the max aperture at 500mm is f7.1 compared to the max aperture of an EF 100-400 with 1.4X extender at f8.
Finally, the dimensions and weight are now known. The RF lens is indeed a bit longer, although the diameter remains the same. Fortunately, it uses the same 77mm front filter. Furthermore, it is actually a bit lighter, at 3.0 lbs. (1365g) versus 3.46 lbs. (1570g) for the EF version, both without tripod mount attached.
As to autofocusing, that will have to wait for real world testing of production lenses.
What's the Bottom Line?
So, all in all, the blanks for the zoom that have been filled in so far, based on specs alone, do not surface any “no-go" characteristics. The new RF lens is roughly comparable in image quality, size and weight to the EF version. If one already has the EF and if adapting it to the RF mount, with either the adapter or the control adapter, does not detract significantly from its autofocusing capability and usability, then there seems only minor reasons to swap out the EF for the RF. On the other hand, the RF version is more flexible since it does not require use of an extender to reach 500mm. In the final analysis, it’s great to have choices!
600mm f11 and 800mm f11!!??
Well, these lenses were a surprise, to say the least. Designed as compact, lightweight and inexpensive alternatives to lenses that cost more than $10,000, they feature a two section barrel that stores collapsed and extends when in use. And, they are fixed aperture f11 lenses; they cannot be stopped down further. But then, who would want to given that this is a stop or so past the optimum aperture where diffraction effects begin to visibly reduce image quality. (Perhaps the best introduction to that topic can be found in Roger Cicala's article here.) Significantly though, the new mirrorless R5 and R6 cameras will autofocus down to f22, so these lenses can autofocus with not only the new RF 1.4X extender but also the RF 2X extender as well.
Introduced at $699 and $899 respectively, reaction has been surprisingly favorable so far. There really aren't any alternatives that provide equivalent reach without the expenditure of quite a bit more money. And, they are compact, lightweight and image stabilized. But, there is a downside. Most lightweight and dim alternatives from other manufacturers are more flexible zoom designs and can be stopped down if desired. And, in addition to the obvious rather dim f11 fixed aperture, these lenses are not "L" quality offerings. As such, they are optical compromises that hold cost down but result in reduced image quality.
If they can meet the needs and expectations of a significant number of potential customers they will enjoy a degree of commercial success. But, for those wanting the best possible optical quality, these lenses will remain on the shelf.
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