# RF and EF extenders on the EF 600/4L IS II



## neuroanatomist (Jan 24, 2022)

After getting both the RF extenders to use with my RF 100-500L, I became curious about whether they would perform better than my EF MkIII extenders when used with my EF 600/4L IS II on my EOS R3. As most will know, the protruding elements of the RF extenders do not fit into the Canon EF-RF mount adapters, even the drop-in filter version that has a much wider opening. I purchased a Commlite EF-RF adapter (which has a wider opening than the other 3rd party adapters or the OEM versions), and modified it with a Dremel until the opening was sufficiently wide to accept the TCs. 

The resolution charts on The Digital Picture allow comparison of the EF TCs on the EF 600/4 III with the RF TCs on the RF 600/4, but they are done with two different bodies, and that complicates interpretation. With the modified adapter in hand, I had the ability to test both sets of adapters with the same lens. Of course, being able to mount the EF TCs in front of the adapter and the RF TCs behind the adapter gave me the opportunity to test the various combinations of stacked TCs as well, which I did. 

I did two sets of tests with all 8 possible combinations of TCs and the bare lens, all at the lens' maximum aperture:

EF 2xIII + RF 2x + EF 600/4 II = 2400mm f/16
EF 2xIII + RF 1.4x + EF 600/4 II = 1680mm f/11
EF 1.4xIII + RF 2x + EF 600/4 II = 1680mm f/11
EF 1.4xIII + RF 1.4x + EF 600/4 II = 1200mm f/8
RF 2xIII + EF 600/4 II = 1200mm f/8
EF 2xIII + EF 600/4 II = 1200mm f/8
RF 1.4xIII + EF 600/4 II = 840mm f/5.6
EF 1.4xIII + EF 600/4 II = 840mm f/5.6
EF 600/4 II = 600mm f/4
For both sets of tests, I used the same enhanced ISO 12233 charts than Bryan uses for the TDP tests, which test resolutions up to 4000 lw/ph. The first set of tests was performed in the same way the TDP tests are done, by changing the distance from the camera to the subject such that the 3:2 region of the chart fills the frame. Note that for the 1.4x and bare lens shots, I needed to switch to a larger chart because the smaller one was closer than the MFD – that resulted in a change in the lighting but the charts themselves are printed such that the resolutions shown are independent of chart size.

Below are the first set of results. I cropped larger regions than Bryan does (about double the size). The image below is scaled down for upload here, the full size version that shows 1:1 crops can be viewed HERE. 




The second set of tests were a more 'real world' approach similar to that used here by @AlanF to test lenses and extenders. For those tests, the distance was kept constant, which is more relevant for something like bird photography where you can only get so close to the subject and must rely on extenders and/or cropping. For these tests, the distance was ~10 m / 33', which was the distance needed to fully frame the smallest test chart (~150 x 100mm). The image below is scaled down for upload here, the full size version that shows 1:1 crops can be viewed HERE.




As expected, stacking two extenders results in a loss of sharpness. However, the 4x magnification increase with the stacked 2x TCs results in about 3x the resolving power of the bare lens. It will be interesting to see how that translates into real-world subjects that benefit from higher magnification, the moon for example.

Looking at comparisons more relevant for everyday use, the EF and RF 1.4x TCs deliver very similar performance. The EF version appears very slightly sharper in the center, the edges are equivalent. There is a noticeable difference between the EF and RF 2x TCs on the EF 600/4 II, with the EF 2xIII delivering sharper results in the center and periphery. The RF 2x actually performs pretty much identically to the two 1.4x TCs stacked (which yields the same final 2x magnification as the 2x TC). Also, though it's not evident from the crops, the RF 2x introduces a noticeable level of barrel distortion that the EF 2x does not. I wonder if that's in keeping with Canon's other RF lenses that leave substantial barrel distortion in the optical design in favor of digital correction (note that I would not consider the RF 2x to have substantial distortion, but it is evident).

For my personal use, I'll stick with the EF TCs when using the EF 600/4 II on my R3, possibly with the RF 2x added behind the EF 2x when I want the maximum focal length I can achieve.


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## Del Paso (Jan 24, 2022)

neuroanatomist said:


> After getting both the RF extenders to use with my RF 100-500L, I became curious about whether they would perform better than my EF MkIII extenders when used with my EF 600/4L IS II on my EOS R3. As most will know, the protruding elements of the RF extenders do not fit into the Canon EF-RF mount adapters, even the drop-in filter version that has a much wider opening. I purchased a Commlite EF-RF adapter (which has a wider opening than the other 3rd party adapters or the OEM versions), and modified it with a Dremel until the opening was sufficiently wide to accept the TCs.
> 
> The resolution charts on The Digital Picture allow comparison of the EF TCs on the EF 600/4 III with the RF TCs on the RF 600/4, but they are done with two different bodies, and that complicates interpretation. With the modified adapter in hand, I had the ability to test both sets of adapters with the same lens. Of course, being able to mount the EF TCs in front of the adapter and the RF TCs behind the adapter gave me the opportunity to test the various combinations of stacked TCs as well, which I did.
> 
> ...


Thanks for the test, you helped me save a few hundred Euros...


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## AlanF (Jan 24, 2022)

neuroanatomist said:


> After getting both the RF extenders to use with my RF 100-500L, I became curious about whether they would perform better than my EF MkIII extenders when used with my EF 600/4L IS II on my EOS R3. As most will know, the protruding elements of the RF extenders do not fit into the Canon EF-RF mount adapters, even the drop-in filter version that has a much wider opening. I purchased a Commlite EF-RF adapter (which has a wider opening than the other 3rd party adapters or the OEM versions), and modified it with a Dremel until the opening was sufficiently wide to accept the TCs.
> 
> The resolution charts on The Digital Picture allow comparison of the EF TCs on the EF 600/4 III with the RF TCs on the RF 600/4, but they are done with two different bodies, and that complicates interpretation. With the modified adapter in hand, I had the ability to test both sets of adapters with the same lens. Of course, being able to mount the EF TCs in front of the adapter and the RF TCs behind the adapter gave me the opportunity to test the various combinations of stacked TCs as well, which I did.
> 
> ...


Thanks Neuro. There was a lot of work there, and most useful - removed any temptation of my buying an EF telephoto and a Commlite. More importantly, it's telling R owners that it might be better to buy EF 600 and 400 f/4 IIIs rather than the RF versions, which are optically the same as they will perform better with TCs.


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## Nemorino (Jan 24, 2022)

AlanF said:


> which are optically the same


Didn't neuro use the 600 II ? The third version has the same glass as the RF 600 has.


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## neuroanatomist (Jan 24, 2022)

Nemorino said:


> Didn't neuro use the 600 II ? The third version has the same glass as the RF 600 has.


Correct, but that is consistent with what @AlanF is suggesting.

My results suggest that the 1.4x TCs are equivalent but the EF 2x is better than the RF 2x. Mounting the extenders behind the 600 III vs. 600 II should not affect the performance of the extender itself. Also, at least according to Bryan/TDP, the 600 II is actually slightly sharper than the 600 III (it seems the latter was primarily designed to reduce weight significantly compared to the MkII, although the MkIII also has less CA and gives an extra stop of IS benefit).

So, since the EF III and the RF are optically identical, if the EF 2x is better than the RF 2x, the EF III may be a better choice for someone who plans to use the 2x TC a lot. OTOH, the RF version is supposed to focus faster than the EF III on an integrated-grip body like the R3.

Personally, I only use the 2x TC for about 5% of my shooting, but that was on my 1D X where the f/8 combo means only the center AF point is available. The R3 will track across the whole frame at f/8 so I may use the 2x more.

If I were buying a 400/2.8 or 600/4 today, I’m pretty sure I’d get the RF version. But since I already have the EF 600/4 II, I was not planning to swap it for the RF version…and these results make me feel even more comfortable with that decision.


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## AlanF (Jan 24, 2022)

Based on my minimal experience of using the EF 2xTCIII in the EF 300mm f/2.8 II and the EF 400mm f/4 DO II and the RF 2x on the RF 100-500mm and RF 800mm f/11, the RF 2x gives less image degradation on the RF lenses than the EF 2x on the EF, but the EF 1.4x and RF 1.4x about the same. Unfortunately in that respect, the RF 600mm f/4 and 400mm f/2.8 are EF lenses and the RF extenders are not optimised towards them.


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## PCM-madison (Jan 24, 2022)

Thank you neuro! This is great information.


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## Click (Jan 24, 2022)

+1

Thank you Neuro.


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## Czardoom (Jan 26, 2022)

AlanF said:


> Based on my minimal experience of using the EF 2xTCIII in the EF 300mm f/2.8 II and the EF 400mm f/4 DO II and the RF 2x on the RF 100-500mm and RF 800mm f/11, the RF 2x gives less image degradation on the RF lenses than the EF 2x on the EF, but the EF 1.4x and RF 1.4x about the same. Unfortunately in that respect, the RF 600mm f/4 and 400mm f/2.8 are EF lenses and the RF extenders are not optimised towards them.


It seems to me, considering how many times this is mentioned on forums, and users have experienced it, that copy variation may be playing a part in Neuro's results, and that he may just have a better copy of the EF 2x than RF 2x. So, I wouldn't necessary assume that the EF 2x is better optically than the RF 2x. All we know is that Neuro's EF 2x is better than his RF 2x.


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## snappy604 (Jan 26, 2022)

fantastic work.. and damn if I'm not curious what you might get with it.. some real world samples with 4x would be neat... the chart results honestly seem pretty good


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## AlanF (Jan 26, 2022)

Czardoom said:


> It seems to me, considering how many times this is mentioned on forums, and users have experienced it, that copy variation may be playing a part in Neuro's results, and that he may just have a better copy of the EF 2x than RF 2x. So, I wouldn't necessary assume that the EF 2x is better optically than the RF 2x. All we know is that Neuro's EF 2x is better than his RF 2x.


Copy variation can indeed be important. Roger Cicala's optical measurements as reported in lensrentals blog show that there is less copy variation in extenders than lenses, but I found copy variation in the three 1.4xTCIIIs I had. I have written several times here that the only copy that counts for you is your own one. Neuro's measurements show that for his copies he should stick to his EF for his EF lens.


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## PCM-madison (Jan 27, 2022)

neuroanatomist said:


> I purchased a Commlite EF-RF adapter (which has a wider opening than the other 3rd party adapters or the OEM versions), and modified it with a Dremel until the opening was sufficiently wide to accept the TCs.


Neuro, can you post a photo that shows how much of the Commlite adapter was removed?


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## neuroanatomist (Jan 28, 2022)

PCM-madison said:


> Neuro, can you post a photo that shows how much of the Commlite adapter was removed?


Quite a bit. I cover that with tape, obviously.


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## AlanF (Jan 28, 2022)

neuroanatomist said:


> Quite a bit. I cover that with tape, obviously.
> 
> View attachment 202268


That's not a job for the fainthearted!


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## Jack Douglas (Jan 28, 2022)

neuroanatomist said:


> Quite a bit. I cover that with tape, obviously.
> 
> View attachment 202268


No reason to faint - it's not that many $$$.  I've contemplated buying one and carefully mounting it on the lathe. Neuro - does that strike you as doable?

Jack


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## neuroanatomist (Jan 28, 2022)

Jack Douglas said:


> No reason to faint - it's not that many $$$.  I've contemplated buying one and carefully mounting it on the lathe. Neuro - does that strike you as doable?


Sure! The adapter has a tripod foot, I just attached a RRS plate to it and put it on a tripod, then took a Dremel to it (with a coarse sanding bit).


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## AlanF (Jan 28, 2022)

neuroanatomist said:


> Sure! The adapter has a tripod foot, I just attached a RRS plate to it and put it on a tripod, then took a Dremel to it (with a coarse sanding bit).
> 
> View attachment 202271


Nikon didn't think into the future for its FTZ adapter. It has a tripod foot that works fine with the Z6 and Z7 series but with the Z9, the foot gets in the way of holding via the built in grip so Nikon has had to bring out a FTZ II without the foot.


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## neuroanatomist (Jan 28, 2022)

AlanF said:


> Nikon didn't think into the future for its FTZ adapter. It has a tripod foot that works fine with the Z6 and Z7 series but with the Z9, the foot gets in the way of holding via the built in grip so Nikon has had to bring out a FTZ II without the foot.


The Commlite foot is removable. Same design as the Canon EF-M mount adapter.


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## snappy604 (Feb 5, 2022)

that is awesome.. so any good results from having such a range? ;-)


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## tron (Feb 17, 2022)

Thanks for the info Neuro. Coincidentally yesterday I ordered Canon Extender EF25 II to put it between EF2XIII and EF1.4XIII to try to increase my 500mm 4L IS II lens focal length for static birds not at infinity of course where the lens will not be able to focus.

EF12 II would probably do the job (EF1.4XIII will be the addon behind the 500/2X/Extender combo) but I could not find it easily (and reasonably cheap) so I took the longer one in case it is being used for macro cases too.

I also have the RX teleconverters but going by the book for now....


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## Jack Douglas (Feb 17, 2022)

tron said:


> Thanks for the info Neuro. Coincidentally yesterday I ordered Canon Extender EF25 II to put it between EF2XIII and EF1.4XIII to try to increase my 500mm 4L IS II lens focal length for static birds not at infinity of course where the lens will not be able to focus.
> 
> EF12 II would probably do the job (EF1.4XIII will be the addon behind the 500/2X/Extender combo) but I could not find it easily (and reasonably cheap) so I took the longer one in case it is being used for macro cases too.
> 
> I also have the RX teleconverters but going by the book for now....


EF 2X ?? Do you actually think you'll gain much from this? There is an old thread, perhaps started by AlanF where some combinations were dealt with.

Jack


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## tron (Feb 17, 2022)

Jack Douglas said:


> EF 2X ?? Do you actually think you'll gain much from this? There is an old thread, perhaps started by AlanF where some combinations were dealt with.
> 
> Jack


My EF500mm f/4L IS II with EF2XIII + EOS-R adapter works admirably with EOS R5 delivering sharp images at 1000mm f/8 or f/9. I have used it many times. It is sharper than my EOS 400mm DO II with EF2XIII and EOS R5.

The only issue is how EF1.4XIII will work on top of that! (It will be a 1400mm f/11 experiment). And how far away it will be its focusing limit. Because it will not focus to infinity. I just hope it will be OK for static small birds...


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## Jack Douglas (Feb 17, 2022)

tron said:


> My EF500mm f/4L IS II with EF2XIII + EOS-R adapter works admirably with EOS R5 delivering sharp images at 1000mm f/8 or f/9. I have used it many times. It is sharper than my EOS 400mm DO II with EF2XIII and EOS R5.
> 
> The only issue is how EF1.4XIII will work on top of that! (It will be a 1400mm f/11 experiment). And how far away it will be its focusing limit. Because it will not focus to infinity. I just hope it will be OK for static small birds...


It's a long time now but some were stacking extenders, I just don't remember how one would find that thread. I think I did a shot with my old 300 2.8 II with 2X and 1.4X with an extension tube and it was fairly good but not up to our usual standard. There is a bit of confusion in your original post - maybe a typo?

Jack


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## tron (Feb 18, 2022)

Jack Douglas said:


> It's a long time now but some were stacking extenders, I just don't remember how one would find that thread. I think I did a shot with my old 300 2.8 II with 2X and 1.4X with an extension tube and it was fairly good but not up to our usual standard. There is a bit of confusion in your original post - maybe a typo?
> 
> Jack



I will try to stack 2 teleconverters (both Canon EF version III series). Not more.

My current biggest (in size and mm) combo is: EF500mm f/4L IS II + EF2XIII + EOS-R adapter + R5: A 1000mm f/8 combo with still L quality and good focusing thanks to R5 (although I had tried it with 5DsR in the past and I had some success)

My experiment: I will put Canon's macro extender tube after EF2XIII and then connect EF1.4XIII. Then I will put the adapter and the R5.
It will not focus at infinity but neither birds are 

Of course as with 1000mm at 1400mm it will be tested for still subjects only.

I do not know if I will have some lack but the cost of the experiment is the one of the macro tube extender (I have everything else).

I remember that you had quite the success with 2X first with your 300mm and then with your 400mm and your 1Dx.
Your superb woodpecker photos are a proof of this.

What combo are you currently using ?


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## neuroanatomist (Feb 18, 2022)

tron said:


> It will not focus at infinity but neither birds are


TCs affect magnification but not the min/max focus distance, so all of the effect is due to the 25mm tube. With that on the 500/4 II, your furthest focus distance will be 9.9 m / 32’. At a 1400mm focal length, that means the largest subject you can fit in the frame and still get in focus is 25 x 17 cm / 9.8 x 6.7”.

Unless the birds you shoot are small ones that aren’t all that far away, I predict a lot of bird headshots in your future. 

Using the EF 12 tube instead would put your far focus distance at 20.6 m / 67.5’, which is why that is the preferred tube for stacking extenders.


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## Jack Douglas (Feb 18, 2022)

tron said:


> I will try to stack 2 teleconverters (both Canon EF version III series). Not more.
> 
> My current biggest (in size and mm) combo is: EF500mm f/4L IS II + EF2XIII + EOS-R adapter + R5: A 1000mm f/8 combo with still L quality and good focusing thanks to R5 (although I had tried it with 5DsR in the past and I had some success)
> 
> ...


I'm shooting almost always with 400 DO II and 2xIII with R5 and my only slight negative is that I think I need somewhat higher shutter speed for good sharpness. I have not stacked the 1.4X in there recently because the need for that magnification is rare but when it warms up I'll make a point again to try it. I have a cheaper extension tube set and I'm a little leery of it breaking.

Jack


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## AlanF (Feb 18, 2022)

Jack Douglas said:


> I'm shooting almost always with 400 DO II and 2xIII with R5 and my only slight negative is that I think I need somewhat higher shutter speed for good sharpness. I have not stacked the 1.4X in there recently because the need for that magnification is rare but when it warms up I'll make a point again to try it. I have a cheaper extension tube set and I'm a little leery of it breaking.
> 
> Jack


I wouldn’t bother. What you gain in focal length is lost to a great extent by increased diffraction and lens aberration with the high resolution sensor. You would gain more on the R6.


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## Jack Douglas (Feb 18, 2022)

AlanF said:


> I wouldn’t bother. What you gain in focal length is lost to a great extent by increased diffraction and lens aberration with the high resolution sensor. You would gain more on the R6.


You are right, it's going to be marginal at best. I'm quite sure I did it long ago and came to the same conclusion although not so firmly because I had the 6D and the 300.

Jack


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## tron (Feb 18, 2022)

neuroanatomist said:


> TCs affect magnification but not the min/max focus distance, so all of the effect is due to the 25mm tube. With that on the 500/4 II, your furthest focus distance will be 9.9 m / 32’. At a 1400mm focal length, that means the largest subject you can fit in the frame and still get in focus is 25 x 17 cm / 9.8 x 6.7”.
> 
> Unless the birds you shoot are small ones that aren’t all that far away, I predict a lot of bird headshots in your future.
> 
> Using the EF 12 tube instead would put your far focus distance at 20.6 m / 67.5’, which is why that is the preferred tube for stacking extenders.


Thank you very much for telling me. Maybe there is time to cancel my order (or keep it for macro but this happens very rarely if not never) and try to get the smaller one. I thought I had read somewhere that the minimum distance was an order of magnitude bigger.


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## Jack Douglas (Feb 18, 2022)

Maybe a dumb question but here goes. Has anyone used the short extension tube to alleviate the restriction regarding the 100-500 with extenders? I suppose there is nothing to gain in that scenario?? I'm still waiting to purchase a 100-500 for my daughter since they are either overpriced or not available.

Jack


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## AlanF (Feb 18, 2022)

Jack Douglas said:


> Maybe a dumb question but here goes. Has anyone used the short extension tube to alleviate the restriction regarding the 100-500 with extenders? I suppose there is nothing to gain in that scenario?? I'm still waiting to purchase a 100-500 for my daughter since they are either overpriced or not available.
> 
> Jack


Jack, have you considered the RF 100-400mm for her - dirt cheap, very light and really sharp? I now have 2 - one for my wife and one for me when I want to walk out really light. By the way, onthe R5, the 100-500mm gives enough reach most of the time without an extender.


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## Jack Douglas (Feb 18, 2022)

AlanF said:


> Jack, have you considered the RF 100-400mm for her - dirt cheap, very light and really sharp? I now have 2 - one for my wife and one for me when I want to walk out really light.


I have and am but so far I don't see any dirt cheap where I live but I'll keep my eye more tuned.

Jack


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## AlanF (Feb 18, 2022)

Jack Douglas said:


> I have and am but so far I don't see any dirt cheap where I live but I'll keep my eye more tuned.
> 
> Jack


They sell between £620-700 here And are readily available.


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## Jack Douglas (Feb 18, 2022)

AlanF said:


> They sell between £620-700 here And are readily available.


Found one only on Kijiji for all of Alberta - $2200 CAD asking, so over 1200 pounds. Hopefully that will begin to change.

Jack


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## neuroanatomist (Feb 19, 2022)

Jack Douglas said:


> Found one only on Kijiji for all of Alberta - $2200 CAD asking, so over 1200 pounds. Hopefully that will begin to change.


Sounds like there’s a misunderstanding. I think you’re looking for an EF 100-400 L lens, @AlanF is suggesting the new(ish) *RF* 100-400mm, a ‘consumer’ type lens that has very good IQ. It’s in stock at Henry’s for $879 CAD. 









Canon RF 100-400mm F5.6-8 IS USM Lens







www.henrys.com


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## Jack Douglas (Feb 19, 2022)

neuroanatomist said:


> Sounds like there’s a misunderstanding. I think you’re looking for an EF 100-400 L lens, @AlanF is suggesting the new(ish) *RF* 100-400mm, a ‘consumer’ type lens that has very good IQ. It’s in stock at Henry’s for $879 CAD.
> 
> 
> 
> ...


Thanks, I can now at my age claim a senior moment. Yes the RF is available and is an option but it starts to become dicey with TCs and she likes to shoot birds like me. I guess X1.4 wouldn't be too bad.


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## Jethro (Feb 19, 2022)

Jack Douglas said:


> Thanks, I can now at my age claim a senior moment. Yes the RF is available and is an option but it starts to become dicey with TCs and she likes to shoot birds like me. I guess X1.4 wouldn't be too bad.


Some of us starting having senior moments long before reaching an extended age!

Pretty sure AlanF has done some detailed analysis on another thread about the RF 100-400 with extenders - he's very positive about the combination.


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## AlanF (Feb 19, 2022)

Jack Douglas said:


> Thanks, I can now at my age claim a senior moment. Yes the RF is available and is an option but it starts to become dicey with TCs and she likes to shoot birds like me. I guess X1.4 wouldn't be too bad.


i wouldn‘t bother with TCs on the RF 100-400mm on the R5, but the 1.4 is useful with that lens on the R6. The larger pixels of the R6 are more tolerant of diffraction.


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## Jack Douglas (Feb 20, 2022)

AlanF said:


> i wouldn‘t bother with TCs on the RF 100-400mm on the R5, but the 1.4 is useful with that lens on the R6. The larger pixels of the R6 are more tolerant of diffraction.


Thanks Alan. I should have mentioned she presently shoots with the R. She is particular about the quality of her shots, probably from seeing so many of mine, so I'm certain based on my own experience that 400 is not enough. Bare 500 would probably be the minimum and 500 X 1.4 much better so we must wait for the 100-500.

Jack


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## jeffa4444 (Feb 28, 2022)

AlanF said:


> Jack, have you considered the RF 100-400mm for her - dirt cheap, very light and really sharp? I now have 2 - one for my wife and one for me when I want to walk out really light. By the way, onthe R5, the 100-500mm gives enough reach most of the time without an extender.


I got the RF 100-400mm f5.5-8 IS USM for hiking as it’s so light & compact. Was extremely surprised at the IQ given the price. Obviously not at the same level as the EF 100-400mm f4.5-5.5L IS USM II or the RF 100-500mm f5.6-7.1L IS USM but completely acceptable.
Duade Paton an Australian bird blogger on YouTube has done a really comprehensive test and he was completely surprised at the results.


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## TexPhoto (Apr 14, 2022)

Thanks for this! have just acquired a 600mm F4 IS II and want to get as much out of it as I can. Right now I have the EF 1.4 and 2X converters and am shooting with an R5. 

I really appreciate the "real world" test where you can see the effects of the magnification. 

Post some photos in the field when you have a chance.


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## Johnw (Apr 17, 2022)

Nice writeup, I'm a fan of TCs when they can save you money. I can't afford any big white lenses at present so I'm using the Sigma EF TCs with the Samyang EF 135/2 adapted to the R bodies when I want larger apertures than the RF 100-400 has.

This is a relatively cheap setup that allows the following fast telephoto options.

135 2.0 - FF
189 2.8 - FF
216 2.0 - Crop
270 4.0 - FF
302 2.8 - Crop
432 4.0 - Crop


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## mandog (Apr 23, 2022)

Thanks for putting this together. I have all but the RF 2x, and I don't think I'll be in any hurry to get one now. It's interesting how the EF2x+RF1.4x preserves the line width of the text, while the EF1.4x+RF2x slims it down, so the former wins for me. I don't see any real benefit to going with the EF2x+RF2x over that (maybe a little less color aliasing, but I'll take double the shutter speed at that FL).

I have tested the RF 1.4x against the EF 1.4x III on the EF 600/4 II using MTF Mapper. I could not see any difference, except in the extreme corners the RF 1.4x was less sharp in my test. Across the rest of the frame, my 1200 dpi test chart was probably limiting. 

BTW, I use the CommLite CM-EF-EOSR ARC adapter (with the control ring, but without the foot) because it only needs relatively minor surgery to fit the RF extender:


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## Johnw (Apr 26, 2022)

I just ordered an RF 2x and one of the Commlite adapters to try this mod myself. This definitely increases the appeal of certain EF lenses, since EF are the only ones you can effectively double stack TCs without extension tubes using this method. For example, if this works for me I will probably pick up the Sigma 150-600 again. Having a 600-2400 lens sounds pretty good.


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## AlanF (Apr 27, 2022)

Johnw said:


> I just ordered an RF 2x and one of the Commlite adapters to try this mod myself. This definitely increases the appeal of certain EF lenses, since EF are the only ones you can effectively double stack TCs without extension tubes using this method. For example, if this works for me I will probably pick up the Sigma 150-600 again. Having a 600-2400 lens sounds pretty good.


2400mm f/25 isn’t going to resolve significantly more than 1200mm f/12.6 by the time increased optical aberration and diffraction have kicked in, and will be horrible to handle. You would do just as well by buying Topaz Gigipixel and upresolving 2x.


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## mandog (Apr 27, 2022)

AlanF said:


> 2400mm f/25 isn’t going to resolve significantly more than 1200mm f/12.6 by the time increased optical aberration and diffraction have kicked in, and will be horrible to handle. You would do just as well by buying Topaz Gigipixel and upresolving 2x.


Agree that 2400mm f/25 is not useful on a modern high-resolution body. You should consider that the 150-600mm zooms essentially have a 1.4x TC built-in to get from 400mm to 600mm, so just putting a TC on it is essentially stacking TCs (not exactly, but close enough to practical reality).

But I disagree that AI upscale with Topaz Gigipixel (or equivalent), is a panacea. Aside from the technical problems it can create, there are ethical issues as well. Unless the viewer expects the image to be artistically interpreted, then using AI in a photo that could reasonably be expected to be in documentary form is not kosher. But I don't mean to send this thread off in another direction, so I won't say more on that here.

Also, I didn't mention that the R5 can see both the EF & RF TC when stacked, and calls them both out in the EXIF, but it doesn't multiply the TC factors to get the total extension factor and effective focal length right. So that could affect AF and IBIS.


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## AlanF (Apr 27, 2022)

mandog said:


> Agree that 2400mm f/25 is not useful on a modern high-resolution body. You should consider that the 150-600mm zooms essentially have a 1.4x TC built-in to get from 400mm to 600mm, so just putting a TC on it is essentially stacking TCs (not exactly, but close enough to practical reality).
> 
> But I disagree that AI upscale with Topaz Gigipixel (or equivalent), is a panacea. Aside from the technical problems it can create, there are ethical issues as well. Unless the viewer expects the image to be artistically interpreted, then using AI in a photo that could reasonably be expected to be in documentary form is not kosher. But I don't mean to send this thread off in another direction, so I won't say more on that here.
> 
> Also, I didn't mention that the R5 can see both the EF & RF TC when stacked, and calls them both out in the EXIF, but it doesn't multiply the TC factors to get the total extension factor and effective focal length right. So that could affect AF and IBIS.


What I was getting at was that if you double up again the focal length of 150-600mm f/6.3 with a 2x TC on it already at 1200mm f/12.6, you increase the number of pixels by a factor of 4 but you hardly improve the resolution with a high resolution sensor and may even make it worse as TCs do degrade images to greater or lesser extents. So, you might just as well increase the number of pixels in post processing by using decent software like Topaz Gigapixel. I don't understand what you mean about ethical issues. Topaz Gigapixel doesn't do anything to alter the image artistically. All it does is to upresolve the image without making it softer. How is that unethical - it's no different from downresolving an image or sharpening it using software, and AI software does it better?


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## mandog (Apr 27, 2022)

AlanF said:


> What I was getting at was that if you double up again the focal length of 150-600mm f/6.3 with a 2x TC on it already at 1200mm f/12.6, you increase the number of pixels by a factor of 4 but you hardly improve the resolution with a high resolution sensor and may even make it worse as TCs do degrade images to greater or lesser extents. So, you might just as well increase the number of pixels in post processing by using decent software like Topaz Gigapixel. I don't understand what you mean about ethical issues. Topaz Gigapixel doesn't do anything to alter the image artistically. All it does is to upresolve the image without making it softer. How is that unethical - it's no different from downresolving an image or sharpening it using software, and AI software does it better?


AI doesn't up-resolve the image--that's not possible. The original scene micro-detail is irretrievably lost when it is down-sampled through the Bayer matrix filter on the sensor. AI takes cues from images in a training set, and applies them to the image to simulate a higher resolution, creating false (but believable) detail. It effectively creates a photo-composite, only at the pixel level. So if you use it on a photo with a bird as the primary subject, it will use feather detail from birds in its training set to produce feather detail that "looks" good. If your bird photo is presented as abstract art, that's fine. But if you are presenting the photo as an accurate representation of that bird in the wild, it's not. If that's too abstract, consider whether it would be ethical to use AI to up-resolve a crime scene photo used in court.


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## AlanF (Apr 27, 2022)

mandog said:


> AI doesn't up-resolve the image--that's not possible. The original scene micro-detail is irretrievably lost when it is down-sampled through the Bayer matrix filter on the sensor. AI takes cues from images in a training set, and applies them to the image to simulate a higher resolution, creating false (but believable) detail. It effectively creates a photo-composite, only at the pixel level. So if you use it on a photo with a bird as the primary subject, it will use feather detail from birds in its training set to produce feather detail that "looks" good. If your bird photo is presented as abstract art, that's fine. But if you are presenting the photo as an accurate representation of that bird in the wild, it's not. If that's too abstract, consider whether it would be ethical to use AI to up-resolve a crime scene photo used in court.


What is your evidence that it is using training on a set of birds to create detail? Do you know what the neural networks are trained on? Are they just working from local general patterns? I can see in the patterns from the Topaz AI sharpening that they are doing a local geometric based sharpening and not reconstructing real feather detail.


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## mandog (Apr 28, 2022)

AlanF said:


> What is your evidence that it is using training on a set of birds to create detail? Do you know what the neural networks are trained on? Are they just working from local general patterns? I can see in the patterns from the Topaz AI sharpening that they are doing a local geometric based sharpening and not reconstructing real feather detail.


From the Topaz web site: "Gigapixel AI’s neural networks are continuously trained on a wide variety of sample images to understand how photorealistic detail looks. After learning from millions of images, our AI image upscaler can now believably increase resolution on a wide variety of different subjects..." There probably are some feathers in those millions of images. Also note that they say it's "believably" increasing resolution. That's telling.


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## AlanF (Apr 28, 2022)

mandog said:


> From the Topaz web site: "Gigapixel AI’s neural networks are continuously trained on a wide variety of sample images to understand how photorealistic detail looks. After learning from millions of images, our AI image upscaler can now believably increase resolution on a wide variety of different subjects..." There probably are some feathers in those millions of images. Also note that they say it's "believably" increasing resolution. That's telling.


What AI is particularly good at is seeing patterns. If there are hidden patterns in interpolating pixels that it detects from say comparing low resolution images with high resolution then it can predict with some credence the best interpolation in various circumstances and not necessary using a database of say feathers. I think that Topaz doesn’t use accurate preset libraries of details as it makes a real mess of introducing artefacts when the settings are too high.


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## Johnw (Apr 29, 2022)

AlanF said:


> That's not a job for the fainthearted!



I used a manual file on mine but the job was pretty easy, took less than an hour. I also had to take off enough to expose the lower electronics so I covered that with a piece of tape to finish it off. I love this mod because now I can use the RF TCs with any EF lens, even ones that did not support TCs originally. With the ones that did, they can be double stacked.



AlanF said:


> 2400mm f/25 isn’t going to resolve significantly more than 1200mm f/12.6 by the time increased optical aberration and diffraction have kicked in, and will be horrible to handle. You would do just as well by buying Topaz Gigipixel and upresolving 2x.



The utility would be limited of course. I'm mainly thinking of brightly lit astro targets like the moon or Venus, and using a tripod or equatorial mount. No hand holding at 2400. There is actually some decent close up footage of the moon at f/25 on youtube, mainly just lacking adequate stabilization to make it better.


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## neuroanatomist (Apr 29, 2022)

Johnw said:


> I love this mod because now I can use the RF TCs with any EF lens, even ones that did not support TCs originally. With the ones that did, they can be double stacked.


On my list of things to try is the RF 1.4x behind the EF 85/1.4L IS for a 120mm f/2. That's really about the only non TC-compatible EF lens I still have worth putting a TC behind. Double-stacking might be fun with the MP-E 65, I don't see a need for it with the TS-E 17 or 24.


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