This article compares the theoretical performance of the Canon 16-35 f/4L IS USM with the 16-35 f/2.8L II by looking at the MTF graphs for the two lenses.
The Canon EF 16-35 f4L IS USM was announced yesterday and it will have a lot of landscape photographers considering upgrading their current wide-angle zoom lens. There were previously just 2 zoom lenses in the 16-40mm range, the 17-40 F4L and the 16-35 F2.8L II. I have owned both and used them extensively. Optically there is little if anything to choose between them in terms of sharpness and contrast when stopped down. The 16-35 produces beautiful 14 points sun stars and has a 2.8 aperture, helpful for astrophotography. The lenses also have a slightly different focal length, but for 90% of landscape shots the images they produce are almost indistinguishable. The 2.8L is similarly sharp at f2.8 as the 17-40 is at f4. Both lenses ‘suffer’ from average edge resolution and soft corners even when stopped down, though in my opinion this is rarely an issue. Nevertheless, that remains the main flaw with these lenses and since the release of some better Nikon alternatives Canon shooters have been clamoring for an upgrade.
MTF curves are theoretical lens performance graphs which, if the real life performance matches the graphs, tell us quite a lot about image sharpness and contrast. Since I currently use the 16-35 f2.8L as my primary (only) wide-angle zoom I decided to make some comparisons with the MTF curves of the respective lenses. As mentioned above the 17-40 is very similar so the results below can be read across. Remember this is ‘just for fun’. MTF curves are theoretical, I assume they do actually stand for something, but I think you have to read the information below with a pinch of salt….
I’m only comparing lenses at 16mm because it takes a long time to do these comparisons and write this blog. I’m also more interested in the 16mm performance because its the focal length I use most but trust me that the MTF at 35mm is equally impressive, perhaps more so.
The below conclusions are somewhat dumbed down, that is to say I don’t explain everything in detail. If you want a better understanding of how I have come to these conclusions have a look at this graphic explaining MTF.
Also understand that I am comparing an f2.8 lens to an f4 lens and so the ‘wide open’ results really shouldn’t be compared directly. It would have been fairer to have the results from the f2.8 lens stopped down to f4, but sadly these curves do not exist.
EF 16-35 f/4L IS vs. 16-35 f/2.8L II – Contrast
The new f4L appears to have outstanding contrast characteristics across the frame and at all apertures at both 16mm and 35mm. It should be slightly better than the f2.8L. Any value above 0.8 can be considered as excellent and the new lens achieves this throughout with only the extreme corner dropping to ‘very good’ when shooting wide open at f4. As long as the flare characteristics are good (and we have every reason to believe they will be due to developments in lens coatings in Canon’s most recent lenses) then we have a lens with outstanding contrast. The result should be vibrant colours and deep blacks as good as the best Canon lenses. That said, since I have never ever been disappointed the contrast of the f2.8L perhaps this won’t matter too much!
EF 16-35 f/4L IS vs. 16-35 f/2.8L II – Sharpness
The ‘sharpness’ MTF curves for the EF 16-35 f4L IS are very impressive indeed. In fact they appear to blow the f2.8L out of the water. Perhaps the most exciting results are those stopped down to f8, the kind of small aperture that most landscape photographers use for the majority of shots. At f8 the 16-35 f4L IS shows a noticeable increase in sharpness in the center but a very significant increase in the corners. The sagittal lines (solid) are going to result in the most objectionable blur and it is here that we see the biggest improvement. In fact sharpness in the sagittal direction should be excellent at f8 all the way to the extreme corner. There *should* be a night and day difference, exactly what everyone was hoping for!
The wide open results are of less interest to landscape photographers and no doubt people might read this an say “you can’t compare one lens at f2.8 to another at f4, that’s not a fair fight”. Well that’s true, but here are the results anyway and it looks like the f4L is, as expected, significantly better.
In fact just for fun here is a comparison between the 16-35 f4L IS at f4 and the 16-35 F2.8L II at f8. The f4L is still better!
That result is surprising and also seems unlikely! There is only one place I have found reliable samples and that’s the Canon Japan site here: http://cweb.canon.jp/ef/info/ef16-35/index.html Regardless of what aperture these images are taken at (and reading the page it seems the left image may be taken at f/4) these samples look extremely promising!
EF 16-35 f/4L IS vs. 16-35 f/2.8L II – Astrophotography
The newer f4L lens is a full stop slower at its widest aperture making it less suited to astrophotography. However the MTF curves show that it is appreciably sharper, particularly in the corners. If you compare it to the 17-40L at f4 (which is a bit of a pig for astrophotography) you see exactly the same magnitude of sharpness improvement. Furthermore, comparing the sagittal lines to the meridional lines indicates that there won’t be the same degree of astigmatism in the corners. The f2.8L wasn’t by any means great for astrophotography, but it was good enough. I doubt the f4L will be any better, but the sharpness improvements should make the 1 stop loss in light gathering ability far more acceptable.
EF 16-35 f/4L IS vs.……
I thought I would do a couple more f8 sharpness comparisons against the best prime and zoom lens offerings Canon have at the wide end
If you compare the red (sagittal) solid lines to all the other solid lines you see it is higher up the graph than all of them from left to right. The same is also true of the dashed lines (meridional) except for at the extreme corner where the 14mm and 17mm TSE are slightly better. Essentially the MTF suggests that the new lens is sharper than every other lens on the graph when stopped down to f8. That’s pretty impressive.
EF 16-35 f4L IS vs. 16-35 F2.8L II – Unanswered questions
MTF doesn’t tell the whole story. Missing lens characteristics include distortion, chromatic aberration, flare and vignetting. However, given the calibre of recent Canon lenses it is hard to see any of these factors being objectionable for landscape photographers. The greatest unanswered question for me is: What will the sun stars look like? For those who like bombastic shots into the sun (like me) then the 14 point pinwheel sun stars of the 16-35 f2.8L were a huge bonus, I can only hope that then newer lens is as good. One thing we do know is that since it has 9 aperture blades whatever sun star it does produce will have 18 points!
Image stabilisation is a huge bonus for what I do. When hiking it can be a pain to be setup and take down my tripod to take images on route during the day. I actually have no issue whatsoever in pushing my 6D to ISO 400 to get reasonable shutter speeds. Having IS of anything approaching 3 stops will allow me to shoot handheld in almost any situation during the daylight hours as long as exposure bracketing or long exposures are not required. That is a great thing in my opinion!
If the MTF curves can be trusted then the 16-35 f4L IS should provide the sharpness upgrade Canon users have been waiting for in their wide-angle zooms and appears to pave the way for a higher resolution sensor. In fact, when stopped down the new lens appears to perform better than some of Canon’s finest prime lenses. Still, these comparisons are theoretical and real life use might show something different. I think I’m going to have to buy one and find out for myself!