The Canon EF mount is alive - the EF 100-400 f/4.5-5.6L IS II USM on the EOS R5

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Canon EF vs RF

With the mir­ror­less sys­tem cam­eras of the R sys­tem, Canon intro­duced a new lens bay­o­net, the RF mount. This is large­ly iden­ti­cal in diam­e­ter and con­struc­tion to the EF mount of the EOS SLR cam­eras, which was intro­duced in 1987 togeth­er with the first Canon EOS cam­era, the EOS 650. The dif­fer­ence is a short­er dis­tance to the film/sensor plane (called flange dis­tance). In addi­tion, the new mount has more elec­tri­cal con­tacts and is claimed to be able to com­mu­ni­cate faster with the camera.

For­tu­nate­ly, all cur­rent­ly avail­able Canon EOS R cam­eras (R, RP, R5, R6) sup­port native com­mu­ni­ca­tion with exist­ing EF lens­es. To com­pen­sate for the dif­fer­ence in flange dis­tance, Canon only needs a pas­sive adapter. In my expe­ri­ence with my cur­rent­ly used 11 Canon EF lens­es, they work at least as well adapt­ed to my EOS R5 as they did with my pre­vi­ous DSLR bod­ies. The speed of the aut­o­fo­cus is also on the same level.

Why am I writing all this?

Well, the switch to mir­ror­less sys­tems for sys­tem cam­eras is in full swing across all man­u­fac­tur­ers. The flip-up mir­ror is a dis­con­tin­ued design, even if many don’t want to admit it. For most brands, it means replac­ing all lens­es if you want max­i­mum aut­o­fo­cus per­for­mance and the best image sta­bi­liza­tion. The avail­able lens adapters are, for exam­ple on Sony and Nikon, only workarounds with lim­it­ed functions.

Not so with Canon: all exist­ing EF lens­es can be used with­out restric­tions (a few ancient exot­ic lens­es exclud­ed). They even par­tial­ly gain in per­for­mance. So I can now use my much-loved EF 85 f/1.2L II and my EF 100 F/2.8 Macro in a sta­bi­lized man­ner on my R5 thanks to the inte­grat­ed IBIS.

In addi­tion, the inge­nious drop-in mount adapter also allows the use of gray / ND or polar­iz­ing fil­ters behind the lens, so I can, for exam­ple, use both fil­ters with my TS-E 17mm and the Samyang 14mm f/2.8 now.

Fur­ther­more, the lens equiv­a­lents of the EF ver­sions in the RF sys­tem cur­rent­ly cost sev­er­al times as much (they are with­out a doubt also often a bit bet­ter) and many focal length ranges are not yet covered.

But appar­ent­ly the word has­n’t got­ten out to every­one that the “old” EF lens­es are still per­fect­ly usable. This leads to the fact that many peo­ple sell their old “lens trea­sures” when switch­ing to the R sys­tem. There­fore, a lot of EF lens­es are cur­rent­ly avail­able on the sec­ond-hand mar­ket at very rea­son­able prices. Thus, I have already recent­ly pur­chased an EF 24-70 f/2.8L II USM sec­ond-hand, and I am still thrilled with its per­for­mance. It is cur­rent­ly my “always on” when I am on the road.

I recent­ly came across an offer for an used EF 100-400 f/4.5-5.6L IS II USM* lens in d good con­di­tion, which again I could­n’t refuse. The lens is also fre­quent­ly offered in good sec­ond hand con­di­tion, eg. on eBay*.

The Canon EF 100-400 f/4.5-5.6L IS II USM

In terms of con­struc­tion, the lens is most­ly com­pa­ra­ble to the Canon RF 100-500mm F4.5-7.1 L IS USM. The mechan­i­cal con­struc­tion of both lens­es is very sim­i­lar, the build qual­i­ty is top notch, but the RF offers 100mm more focal length, but then only at an max­i­mum aper­ture of 7.1. How­ev­er, the RF costs three times what I paid for the used, but in per­fect con­di­tion, EF lens. Opti­cal­ly, up to 400mm, both lens­es are com­pa­ra­bly extreme­ly good. Even with Exten­der, the EF is still per­form­ing very well, as the fol­low­ing exam­ple shows:

Blue tit, EF 100-400 f/4,5-5,6L IS II with 1,4x Exten­der III, 560mm, f/9.0, 1/500, ISO 3200, 2000x3000px crop

Since I already cov­er the 100-400mm focal length range well with my Sig­ma 60-600mm f/4.5-6.3 DG OS HSM Sports and my 400mm f/2.8L IS II USM, I thought long and hard about whether the 100-400 made sense. But then the price was too good to pass up.

The advan­tage of the 100-400 is nat­u­ral­ly the sig­nif­i­cant­ly low­er weight (1,590g) com­pared to the Sig­ma (2,700g) and the small­er size. In the 100-400mm range, the Canon is opti­cal­ly even bet­ter than the Sig­ma, which is not sur­pris­ing giv­en the 10x zoom range of the Sig­ma. Where­as I was quite sat­is­fied with the Sig­ma so far:

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Robin (Sig­ma 60-600 at 600mm, f6.3, 1/1000, ISO 5000)

From 401mm upwards, how­ev­er, the Sig­ma prob­a­bly has an advan­tage, although….

More about this later

A first test

Hav­ing now received the Canon EF 100-400 f/4.5-5.6L IS II USM, I briefly test­ed it in our back­yard with the local birdlife. Because of the bad weath­er, this was also imme­di­ate­ly a real tough test. I had to turn up the ISO up to 3,200 to 4,000 at times. I there­fore denoised all the images in DxO Pho­to­Lab 4, and after­wards post-processed them in Light­room Clas­sic, as has proven to get the best results. By the way, all pic­tures were tak­en hand­held with­out a tri­pod. The IS of the Canon 100-400 in com­bi­na­tion with the IBIS of the R5 is also outstanding.

First a pic­ture of a great tit at 400mm (already sig­nif­i­cant­ly cropped): 

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Great tit, 400mm, f/5.6, 1/200, ISO 800 

And for bet­ter com­par­i­son a 100% crop: 

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Great tit, 400mm, f/5.6, 1/200, ISO 800, crop 100% 

Can we do more - with extenders?

The Canon DSLRs could only focus at an aper­ture of at least f/5.6. Only the high­er-qual­i­ty 1 series bod­ies could still focus with an open aper­ture of f/8, but then only using the cen­tral AF fields. In addi­tion, the image in the opti­cal viewfind­er got very dark.

There­fore, I would nev­er have thought of using an exten­der on a 100-400mm f/5.6 that reduces the aper­ture by 1 f-stop (1.4x) or even 2 f-stops (2x). This is now much dif­fer­ent with the new mir­ror­less bod­ies. These allow to use aut­o­fo­cus still at aper­tures of f/11-f/22, which is what makes the new exot­ic lens­es like the RF 600mm f/11 IS and the RF 800mm f/11 IS rea­son­able to use. Well, 800mm f/11, that could also be done with the 100-400 with 2x extender…

So I have now also tried my exist­ing exten­ders with the EF 100-400 f/4.5-5.6L IS II USM. The results have real­ly stunned me!

First of all a blue tit at 560mm (with Canon Exten­der EF 1.4x III, already sig­nif­i­cant­ly cropped to 3,600x2,400 pixels:

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Blue tit, 560mm, f/8, 1/500, ISO 3,200

And now a 100% crop (1200px wide) tak­en with the R5: 

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Blue tit, 560mm, f/8, 1/500, ISO 3.200 , 100% crop.

That looks almost bet­ter than with­out the exten­der, does­n’t it? Maybe there’s more pos­si­ble? There­fore also anoth­er test at 800mm with the Canon Exten­der EF 2x III, this time a great tit posed once again. This time the image is cropped to 5.700x3.800px:

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Great tit, 800mm f/11, 1/500, ISO 4,000

For com­par­i­son again the 100% crop (1200px wide):

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Great tit, 800mm f/11, 1/500, ISO 4,000, 100% crop

I con­sid­er the result to be incred­i­bly good. In the future, I will not hes­i­tate to use the 100-400 with the con­vert­ers. It’s also amaz­ing, what you can get out of the R5 at high ISO val­ues thanks to the denois­ing with Deep­Prime in DxO Pho­to­lab 4. Here’s anoth­er exam­ple of the same great tit, this time even at ISO 8,000, again a sig­nif­i­cant crop (approx. 2,800x4,300px):

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Great tit, 800mm f/13, 1/800, ISO 8,000

And again, a 100% crop:

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Great tit, 800mm f/13, 1/800, ISO 8,000

It’s unbe­liev­able what is pos­si­ble with the lat­est cam­eras and mod­ern soft­ware today!


I am very hap­py about the new addi­tion to my lens pool. The 100-400 is much more com­pact than my Sig­ma 60-600 or even my Canon 400mm f/2.8, but it deliv­ers first-class image qual­i­ty. And that even with the exten­ders at up to a focal length of 800mm.

In addi­tion, I can still use it on my trusty EOS 5DSR, which I still like to use as a sec­ondary body - but there it prob­a­bly does­n’t make sense to use it with the exten­ders. I am still extreme­ly hap­py about the price drop of the EF lens­es and will con­tin­ue to observe the mar­ket close­ly in the future. Maybe there is still one or the oth­er bar­gain - I will report 😉

Final­ly, a last pic­ture of a sun­flower with the 100-400. It also excels in the close-up range:

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Sun­flower, 214mm, f/5.6, 1/125, ISO 100

*= Affil­i­ate link

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