TCs on the 100-400mm II


Stay at home
CR Pro
Aug 16, 2012
The 100-400mm II looks like having a useful future because all accounts are that it focuses fast and well with a 2xTC on the R5. As I am contemplating purchases with the R5, I wanted to know more about its IQ with the 2xTC to help my choice of gear. Unfortunately, the standard websites, like TDP, are not that useful for comparisons because they use monochrome charts at unknown distances, and lenses' performance can vary a lot with distance.

So, I decided to put the lens through a series of tests with TCs and compare it with the Sigma 150-600mm C, benchmarked against the Nikon 500mm f/5.6 PF, which is reckoned to be up with the very best primes. The EF lenses are on the 5DSR, which is of similar resolution to the R5, and the Nikon on the Nikon D850, whose 45 Mpx sensor is again up there with the very best. The target was a British £10 note, which has lots of different types of detail, colouring and shading. But, when I started to make a collage of the results, PS clammmed up with a notice it was illegal to process pictures of these notes. Sure enough, it is a criminal offence to reproduce even fragments! Here then is just a summary.

At a distance of 3.2m (10 feet), the results with the TCs were very disappointing. Adding, the 1.4xTCIII to the 100-400mm II hardly increased resolution, and the 2xTCIII if anything lowered resolution and contrast despite the 2x 2 larger image. The Sigma was actually better, and adding the Sigma 1.4xTC was quite good. The Nikon PF at 500mm and with a 1.4xTC at 700mm, absolutely blew them away - which didn't surprise me as I get very sharp images of butterflies and dragonflies with it at that distance. So, I was a b it despondent.

At a distance of 19m (60 feet), the situation fortunately changed dramatically. Adding the 1.4xTCIII to the 100-400mm II gave an image that had poorer contrast than 500mm on the Nikon, but after sharpening with the lens sharpening tool in DxO PL, it was pretty close to the 500mm prime, which I knew from experience. And, the resolution was nearly as good. The same was true with the 2xTCIII on the 100-400mm II compared with the 500mm + 1.4xTC - a pretty good performance with the 100-400mm II with a 2xTC, it sharpens up really nicely. The Sigma at 600mm was similar to the Canon at 560mm, which I knew from experience. But, adding the 1.4xTC did not improve it.

So, Canon's TCs do what is logical, they work well at long distances, and I am going to be happy using the 2xTC on an R-series with my favourite zoom. And, be careful with those TDP charts because they might not work for your shooting distances.


CR Pro
Mar 31, 2019
A quick grab shot,
R5 with EF 100-400mm II + 2 x TC III @ 1/1250 F11 800mm ISO 1280
Focus very fast and seems like no need to buy the 800 F11

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