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ISv · Apr 1, 2026

I don't know if @foda has success with the Orange-cheeked Waxbill but today I didn't (~40 min. searching). Took just few photos of House finch (two different males separable not only by the color: different amounts of dirt on the bill

! They did choose the same broken branch for posing. I still have no photo of House finch with yellow instead of orange/red colors on the head, despite seen few!

neuroanatomist · Apr 1, 2026

This is what shows up on my R1 with lens that forces distortion correction attached (not as obvious in the iPhone pic, but the Distortion correction option is grayed out):

ISv · Apr 1, 2026

AlanF said:
A Little Grebe was trying to swallow a fish that was too large. It bit off its head, a gull swooped to steal the fish, and the Grebe dived faster than a U-boat (R5ii + RF 200-800mm).

View attachment 228683 View attachment 228684 View attachment 228685

Nice photos/story with happy ending

. I don't like the gulls when they behave like kleptoparasites! On other hand I have a lot of fun watching videos of them stilling from people on the beech

jeff89 · Apr 1, 2026

I like many would buy the Sigma 300-600 f4 and personally, the Sigma 135 f1.4 Art (I have the EF 135, RF 135 and Sigma EF 135 Art) and would pair it with my Sigma EF 105.

I wouldn't pay Canon's price for the RF 100-300 f2.8 before the tariff increase, as I have the Sigma EF 120-300 2.8 and I won't pay for the Canon RF 300-600 f???, as is would be a want and not a need. I have 2 of the EF 200-400 f4 1.4x, the EF 300 f2.8 and the EF 400 f4 DO and I refuse to pay over $11,000 for a lens, but at $6599 for the Sigma, I would buy that, provided it integrates well. Sony limits the AF speed on it, so I won't buy the Sony version. In fact, I was seriously considering the Lumix S1 II, or maybe the S1R II given the alliance and the fact that it is optimized for the Lumix.

I will hold off for now, to see if they release it for the RF mount, if it doesn't happen, then I will buy a Lumix down the line and begrudge Canon for it.

Oh, and I know a retired Canon USA exec, I never asked for any scoops, I didn't think it was appropriate, but was told, "Pay attention to Canon Rumors." So you might have more pull than you know

ISv · Apr 1, 2026

P-visie said:
When I visited the Isle of May with a small group of photographers, a tern shat on the front of the lens and the inside of the lenshood of one of the groups members. He had a hard time cleaning the lens and the black velvet of the lenshood. It was a Nikon, the terns did not dare shizzle on a Canon.

Do not challenge the terns...

InternalRevenue · Apr 1, 2026

zapper said:
My Sigma RF-S 10-18 f2.8 and 18-50 f2.8, when mounted on my R7, show "Not available with the attached lens" for distortion correction, and "Cannot correct - no data" for Digital Lens Optimizer, in the Lens aberration correction menu. This doesn't bother me much, as I shoot raw and process in Lightroom, which does apply the corrections.

My Sigma 17-40 also shows "not available" for distortion correction, however if you compare the RAW with an OOC JPEG you'll see massive distortion at 17mm being straightened, so this seems to be more of an “always on" situation, as with the RF-S 18-45.

DocInfoSci · Apr 1, 2026

Out of curiosity, is it known whether “Canon allows…” means official support such that the lenses will be forward compatible like Canon’s EF or RF lenses or does it mean Sigma & co. need to guess and Canon simply won’t sue them?

AJ · Apr 1, 2026

I'm still scratching my head.
1) Sigma already has spent the R&D money to develop full-frame lenses like 300-600/4
2) Sigma already has spent the R&D money to figure out the RF mount, as evidenced with their RF-S lenses.

So why aren't they putting 1 and 2 together? I don't see this being a Sigma issue. It seems logical the issue lies elsewhere.

mclaren777 · Apr 1, 2026

I would gladly buy the Sigma 300-600mm if they released it in either EF or RF mounts.

Dragon · Apr 1, 2026

Ron888 said:
Has no one noticed what day it is? lol

True, but the relevant conversation with the Canon exec was reported well before April 1, so the article is legit.

Dragon · Apr 1, 2026

zapper said:
My Sigma RF-S 10-18 f2.8 and 18-50 f2.8, when mounted on my R7, show "Not available with the attached lens" for distortion correction, and "Cannot correct - no data" for Digital Lens Optimizer, in the Lens aberration correction menu. This doesn't bother me much, as I shoot raw and process in Lightroom, which does apply the corrections.

I think that answers my question. Unless the lens is relatively distortion free, that missing bit, while not much of an issue for a RAW still shooter, is a big deal for video. Simply due to lens size implications, this would be a bigger issue for FF lenses than for APS-c. A number of Sigma's EF lenses were quite good, and relatively distortion free, they were also big and heavy. Given that Canon is taking full advantage of electronic correction, that gives them both a size and cost advantage over a third party that is obliged to do all correction optically due to lack of access to the electronic correction capabilities of the camera. As an aside, I have a fair number of 3rd party EF lenses that will not work correctly on either RF or EOS-M mount cameras and all my Canon EF lenses work normally on both mounts, so even the EF protocol had some undiscovered features that the 3rd parties didn't catch and now have no interest in fixing. DPAF definitely messed with the AF algorithms that both Sigma and Tamron were using. FD lenses work fine on RF

.

Ron888 · Apr 1, 2026

Has no one noticed what day it is? lol

zapper · Apr 1, 2026

Dragon said:
So a question. The RF mount clearly provides for extensive geometric correction (and I believe even includes correction for focus shift) in-camera and the data to support that correction clearly resides in the lens, since I don't have to upgrade my camera firmware every time Canon comes out with a new lens. The question is, do the Sigma and Tamron APS-c lenses supply that correction info the camera or just depend on being good enough optically to not perceivably need in-camera correction.? Lack of that tech would be a much bigger deal for FF than for APS-c. It is pretty clear that Even Canon has not yet exercised all the features of RF mount, so until there is a very large body of Canon bodies and lenses to evaluate, it would be very risky for 3rd parties to release lenses that could be rendered obsolete with the next camera release.

My Sigma RF-S 10-18 f2.8 and 18-50 f2.8, when mounted on my R7, show "Not available with the attached lens" for distortion correction, and "Cannot correct - no data" for Digital Lens Optimizer, in the Lens aberration correction menu. This doesn't bother me much, as I shoot raw and process in Lightroom, which does apply the corrections.

Martin0815 · Apr 1, 2026

Canon Rumors said:
"Ported" and being able to actually make enough are different things. A lens like the 135 f/1.4 would be a very difficult lens to make within tight tolerances. Sigma made nothing worth owning for most of the EF days. When they did start making things that were sort of nice there were already 100+ million EF lenses. Having worked directly with Gentec, I know how few lenses they sold in the grand scheme in at least one market (maybe 2). It was peanuts.

Demand increasing 30% is great, now you have to scale everything else 30%. There's a point in lots of businesses where the next step costs exponentially more than the previous one.

Take a company like Leica (yes, they do it different). They make 40 cameras a day. Major products usually take about a year to meet the demand. How much would it cost them to increase production to 60 a day? A boatload. Sigma is closer to Leica than they are to Canon. Leica's revenue is actually higher than Sigma's.

Sorry, I have the completely opposite opinion.
Why should Sigma (or any other 3rd party lens manufacturer) be 'required' to make enough RF lenses to fulfill a very high demand in short time?
Sigma would simply sell as many lenses as they can make, be very happy with the revenue, and later they can decide to increase production capacity if the demand justifies it.

In a free market, any supplier can offer as many product units as he wants, while there is no obligation to produce a very large quantity, even if an initial short supply might disappoint some prospective buyers. After a while production capacities will adjust to the demand.

Additionally, all RF and RF-S cameras use the same RF mount, only the image circle of an RF-S (APS-C) lens is smaller than FF.
Consequently, there is no additional 'technical difficulty' to overcome or any 'reverse engineering' needed for FF RF compared to APS-C RF-S. Note that there are already several 3rd party autofocus RF-S lenses available, e.g. Sigma 15mm f/1.4 DC, so 3rd party manufacturers have already solved the 'technical difficulty'.

zapper · Apr 1, 2026

I did some searching for lens sales numbers. An estimate for Sigma is ~1 million/year, across all mounts, including legacy DSLR. For Canon, ~7 million/year. So your hypothesis that Sigma's production capacity is a limiting factor seems plausible. In that scenario, the Sigma RF-S lenses make sense, as Sigma stands to sell many without competition from Canon. I've two of their RF-S lens, including the 18-50mm f/2.8, but I wouldn't have bought it if Canon had an APS-C 16-50mm f/2.8 as Nikon does.

Kiton · Apr 1, 2026

I am onboard for a
200-400 f4 no built in converter
2nd place a 100-500 5.6 constant aperture.
3rd place their 300-600 f4, a bit overkill for NHL but would be good for football and soccer!

neuroanatomist · Apr 1, 2026

justaCanonuser said:
nice frog in the green, but it looks like sharpness isn't exactly on the frog's eye, so the camera's AF struggled a bit

Yes, that was subsequently corrected with AFMA.

Dragon · Apr 1, 2026

So a question. The RF mount clearly provides for extensive geometric correction (and I believe even includes correction for focus shift) in-camera and the data to support that correction clearly resides in the lens, since I don't have to upgrade my camera firmware every time Canon comes out with a new lens. The question is, do the Sigma and Tamron APS-c lenses supply that correction info the camera or just depend on being good enough optically to not perceivably need in-camera correction.? Lack of that tech would be a much bigger deal for FF than for APS-c. It is pretty clear that Even Canon has not yet exercised all the features of RF mount, so until there is a very large body of Canon bodies and lenses to evaluate, it would be very risky for 3rd parties to release lenses that could be rendered obsolete with the next camera release.

I think most of the folks complaining have been assuming that a licensing deal includes access to the technology and the comments you refer to clearly refute that. That said, figuring out the protocol may be much harder that some think, since the communications could well be encrypted. That pin that switches back to EF protocol may be more complex than many think. It is notable that the folks who got shut down (Samyang, et al) were simply using EF protocol with an RF mount and Canon would have been perfectly justified in zapping them for misrepresentation.

neuroanatomist · Apr 1, 2026

Kingsix88 said:
If I remember correctly, when Canon first came out with the RF mount, these was something strange with the image on third party lens. Unexpectedly strong vignetting and purple hue. I believe it has something to do with canon sensor technology and mirrorless cameras having much shorter distance between rear element and sensor. So light rays hit the sensor at much sharper angle, compared to dslr. Sony didn’t have that issue. It is possible canon mount requires different lens design in certain focal lengths for adequate performance. This is not worth it for a third party lens manufacturer to do. Maybe crop doesn’t have the same issue.

I don’t think so. When the RF mount first came out, there were no third-party lenses for it. That is a recent development, and only for crop lenses.

What you are referring to are issues with peripheral image correction on third-party EF lenses, those were caused by the camera incorrectly identifying the lens. Such lenses spoof Canon lens ID numbers, and the RF mount made that problematic.

Since those were EF lenses, they required the mount adapter, and thus the distance from the lens to the sensor was the same as that on a DSLR. Optics was not the problem, electronics/software was the issue.

justaCanonuser · Apr 1, 2026

neuroanatomist said:
I had one for a while. Bought it used and sold it a couple of years later for the same price that I had paid, essentially a free long-term rental.

I liked that it was the same size as my EF 24-105/4L IS. I was not a fan of the very busy bokeh, evident in the foreground here.

“Ribbit”
View attachment 228688
EOS 7D, EF 70-300mm f/4.5-5.6 DO IS USM @ 300mm, 1/500, f/6.3, ISO 640

nice frog in the green, but it looks like sharpness isn't exactly on the frog's eye, so the camera's AF struggled a bit

justaCanonuser · Apr 1, 2026

Celts88 said:
The RF 600 f/4 would be the ideal lens for bird photography but it's super expensive and out of my price range (it's USD$14k here in Australia). I appreciate the EF 600 f/4 mkIII is essentially the same lense with built in adaptor but don't see any of the mkIII here in Oz, only mkII.

According to CIPA, the RF version has a tad better IS, but in real life it shouldn't make any noticeable difference. I have the EF 600mm f/4.0 III, and I love this lens, its IS is quite impressive. Btw the mk II lens, which still was based on the conventional tele lens design with many big lens elements on the lens' front, is said to be a bit sharper. But it is heavier and on top more front heavy than the mk III lens, so shooting it hand-held is harder.

Celts88 said:
I don't see any issue with fogging but I live in Perth Australia and we very seldom have humidity here, unlike up North or over East. I've got an R1 so dim light doesn't affect me the same way with your R6

The RF 200-800mm is a fantastic lens for the price and I'd highly recommend it, as long as you appreciate it won't have the same pin sharpness or butter smooth Bokeh of the big white primes but you wouldn't expect that from a USD$2k lens. It's so easy to hand carry all day, and being able to go from 200mm to 800mm in a couple of turns is super useful.

I have an RF 200-800, too, for occasions when I want a lighter lens and the flexibility of such a zoom. It is a real fun lens and sharper @ 800mm than I expected, but of course my 600mm prime is much sharper, even with 1.4x TC my EF 600mm f/4.0 III delivers noticeably sharper images @ 840mm. That said, in real life photography, what is more important than lab tests, the 200-800 performs very well, much better than its specs promise. There is only one drawback: from comments I learned that obviously lenses with different quality are out in the wild - I was lucky to get a really good copy that is quite sharp @ 800mm.

Celts88 said:
Primes are fantastic for what they do, but the zooms are so versatile in giving more options within the one lens. It's getting to the stage that the new zooms are only just a fraction less in image quality and if not a professional and making money from your shots then are the way to go, in my opinion.

One advantage of zooms is when you shoot birds in flight, you can catch it using a shorter focal length and then zoom to longer focal lenghts. With a about 800mm prime it is a real challenge to find the bird in the viewfinder.

Kingsix88 · Apr 1, 2026

If I remember correctly, when Canon first came out with the RF mount, these was something strange with the image on third party lens. Unexpectedly strong vignetting and purple hue. I believe it has something to do with canon sensor technology and mirrorless cameras having much shorter distance between rear element and sensor. So light rays hit the sensor at much sharper angle, compared to dslr. Sony didn’t have that issue. It is possible canon mount requires different lens design in certain focal lengths for adequate performance. This is not worth it for a third party lens manufacturer to do. Maybe crop doesn’t have the same issue.

Raptors · Apr 1, 2026

neuroanatomist said:
A camera body will show F00 and manual focus (MF) when it cannot communicate with a lens, which could be because there is no lens attached, because the lens is fully manual, or because there's a problem with the lens itself.

I went out birding over the weekend, mounted my usual combination of 600/4 II, 1.4xIII and the vanilla EF-EOS R Mount Adapter to my R1 and headed out. When I turned on the camera, it showed F00 and MF. I thought, "Oh, sh!t," and swapped on the 2xIII. That worked...but then it also changed to F00 and MF. So I mounted just the bare lens...and that was perfectly fine so I spent the day shooting like that.

When I got home, I cleaned all the contacts and tested various combinations again, including changing out the vanilla mount adapter for the drop-in version and my 3rd party adapter modified for an RF extender to fit behind it.

The upshot was this, and the situation is seemingly stable (through many trials over a couple of days, no changes). Happens on both the R1 and the R8, and with all three of the mount adapters.

Bare 600/4 II – functions normally

600/4 II + 1.4xIII – F00 and MF

600/4 II + 2xIII – varies between:

Normal function

Showing an aperture value that can be adjusted, but still only MF

F00 and MF

The variation is caused by physical manipulation – twisting the lens in the mount or moving the lens, e.g., lifting it from pointing down into shooting position, affects the functionality

600/4 II + RF 1.4x (with Commlite adapter) – functions normally

The fact that I see this behavior with two bodies and three adapters suggests the problem is the TCs or the lens.

I haven't used the 2xIII TC quite some time, not since Comet C:2023 A3 Tsuchinshan-ATLAS in October 2024. So maybe the 2xIII failed sometime over the past 18 months (while sitting mostly undisturbed in a Pelican case with a dehumidifier unit), and the 1.4xIII failed sometime in the past 3.5 weeks since I last used it.

If it's the lens and not the TCs, the problem is specific to use with EF TCs and yet the problem exhibits different symptoms with the two TCs, and I don't know why that would be the case. Admittedly, I would prefer it to not be the lens, because the service life for the 600/4 II ended last year, so sending it to Canon is not an option. I could replace it with the RF 600/4, but I suspect we'll see a version of that lens with the 1.4x TC and hopefully fairly soon. I would love to have the latter and would not love buying twice.

One other idea occurred to me, literally as I was typing this post. I started to write that I don't have any other TC-compatible EF lenses with which to test the extenders...and realized that while that is true, I do have three other EF mount lenses that are physically compatible with the extenders, but don't report them to the camera body (TS-E 17, TS-E 24 and MP-E 65). So I tried the 1.4xIII and the 2xIII with the TS-E 24, and I found that the 1.4xIII shows F00, and the 2xIII shows an aperture value that can be adjusted.

It seems rather unlikely that both TCs independently failed, but I am thinking that's exactly what has happened. Sort of a Sherlock Holmes, "When you have eliminated the impossible, whatever remains, however improbable, must be the truth," sort of thing.

From a practical standpoint, assuming that I'm correct and both extenders have failed, I see no need to replace the 2xIII. One option would be to replace the 1.4xIII ($480 new or $280 used), but I can also just use the RF 1.4x behind my modified Commlite mount adapter, and just remember that I'm doing that since it's not reported in the EXIF. The downside to the latter is that I would not benefit from the DxO lens profile for the combo (though I could batch edit the EXIF and I suspect that DxO would use the 600 II + EF 1.4xIII profile, it still won't be the right profile).

Thoughts, suggestions, and sharing prior experience welcome!

Edit: the RF 1.4x itself does show up in the EXIF, but the exposure information doesn't reflect it, remaining 600mm f/4.
View attachment 228668

I do not own a 600mm lens but recently traveled to South Africa in July 2025 and used the RF 100-300mm 2.8 (CPS trial run) lens. I mounted it with the RF 1.4x on my R1 and the RF 70-200mm 2.8 Z on my R52.

On the second day of shooting, I started experiencing multiple errors, including Err60, Err70, Err 80, and FOO. The R1 would give me an error, shut down, and wouldn’t turn back on. Of course, this happened during a cheetah kill! I swapped cameras to the R52, hoping the contacts on the R1 needed cleaning.

I returned to camp, cleaned the contacts on the R1 and 1.4x, and went out the next day. Unfortunately, the same errors occurred. This time, I also swapped cameras, but this time, I also got errors on the R52.

I contacted Canon South Africa, but since they couldn’t see the lens, they couldn’t really help me. However, they did mention that a new firmware was coming next week that might potentially fix the problem.

Interestingly, when I mounted just the bare lens (100-300 2.8), no errors occurred on either the R1 or R52.

When I returned to Canada, I sent my R1, R52, 1.4x, and their 100-300mm 2.8 to Canon Canada. Their findings were that, since they couldn’t replicate the errors I was getting, it had to be the 1.4x.

The fact that I have no problems with the 1.4x, I still believe the problem was with the 100-300mm 2.8. As I don’t own this lens, I cannot do any further testing.

Hope you get this sorted out!

justaCanonuser · Apr 1, 2026

AlanF said:
The R5ii has the reputation of having the fastest AF to lock on to a target of the A1ii/Z9/Z8 class. I saw this myself recently:

It is fast, no question, but as I said the difference isn't noticeably big when we shot w/o TC side by side. But with TC, the difference is massive. Well, the Z8 is an older model, and Nikon struggled with the AF system in their first Z cameras anyway.

AlanF said:
So, maybe the difference in inherent camera AF is the answer, so you have more control experiments to do.

We'll do

AlanF said:
By the way, Canon has produced a tele zoom with a DO optic, the EF 70-300mm f/4.5-5.6 DO IS USM in 2004.

Ah, thanks, I missed that one.

justaCanonuser · Apr 1, 2026

neuroanatomist said:
One thing that would set it apart is the ability to extend the focal length further with TCs. For the target audience, that may be sufficient.

that's true, I agree

neuroanatomist said:
Consider the Canon 600/4L IS that went from 5.4 kg (MkI) to 3.9 kg (MkII) to 3.1 kg (MkIII, RF) without DO. The 600/4 DO prototype from 2015 (between II and III) was much shorter but reportedly just under 3 kg.

I know, Canon revolutionized the common tele lens design with the EF 600/4 III by moving main parts of the front lens elements (for corrections) back to the middle of the lens, what allowed for much smaller and lighter lens elements (and a much better balance). Sony and Nikon copied that idea with their latest 600/4 lenses, of course in a way they could work around Canon's patents. Nikon upped it by adding a built-in 1.4x TC, what made their Z 600/4 a bit heavier - but this is a smart move, no question, like Canon did it when they brought out their EF 200-400/4 zoom.

neuroanatomist said:
The supertele lenses all used to have a meniscus lens in front (essentially a flat piece of glass to protect the first refractive element, a permanent clear front filter). Dropping those from the design was a significant part of the weight saving for both Canon and Nikon lenses.

Yepp, my old battered EF 500/4.5 still has one.

neuroanatomist said:
So, a 300-600/5.6 DO would probably weigh in somewhere close to the existing 100-300/2.8, but could be shorter. Personally, though a conventional 300-600/5.6 would not really interest me, a DO version that was shorter than my 100-300/2.8 (or even the same length) would tempt me.

Well, I guess we'll have to wait and see with what Canon comes up (if), but it is always fun to speculate with all of you here in these threads.