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DocInfoSci · Apr 14, 2026

AJ said:
Thanks! I'll give DLO a try on some of my old files.

Sure thing! With my R6 and my general subjects I usually just keep in-camera DLO to max, and for serious editing on something special I run the image through DPP to get a DLO-ified TIFF that I then play with elsewhere.

Canon's DLO optimizes for the most interesting things, even with EF lenses. It will often correct lenses for fuzziness caused by weird stuff like field curvature. The primary reason the 20mm f.28 USM is "soft" is because its focal plane is very curved, and the likely reason people find f/8 or f/11 to be "sharp" is that at those settings on an UWA lens the DOF includes much of the area affected by the curve (the curve and DOF start to overlap relative to the focal point). You can actually test this for yourself by setting the lens to f/2.8 and shooting a scene with an arc of something — plastic cups, for an example — and adjust their relative arc until most are in focus; or alternatively place them in a line and keep bumping the f-stop. There are other factors, like how Canon struggled with corners for years, and so forth. Anyhow, Canon's DLO as of the R series knows of this fact and makes seemingly progressive sharpness adjustments to the image to better placate modern taste with a few tricks of illusion. DLO also deals with other shortcomings, such as the vignetting, coma to a degree, etc.

Playing in this manner also teaches one a lot about how Canon can / is using DLO as a sophisticated crutch for hybrid lenses like the VCM series, which by design make use of distortion correction as needed to keep barrels the same size across the series for consistent use with video equipment.

Again, this isn't a top-shelf L lens and never will be — DLO works with what it has — but with DLO I find it's a very pleasant personal interest lens for when the mood strikes.

Michael Clark · Apr 14, 2026

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.

The non-IS Super Telephotos had a flat plate. They were designed in the pre-digital era when reflection off the front of perfectly flat filters in front of digital sensors was not an issue since film was still used in all EOS cameras in 1996 and earlier.

The almost flat plates which were ever so slightly meniscus to avoid reflections from the front of a sensor stack bouncing off the back of the protective plate only appeared on the front of the original IS Super Telephotos introduced in 1999. On the spec sheets, Canon still called them a protection glass. In 2004 Chuck Westfall gave the following list of Canon lenses with the protective meniscus:

EF300mm f/2.8L IS USM
EF400mm f/2.8L IS USM
EF400mm f/4 DO IS USM
EF500mm f/4L IS USM
EF600mm f/4L IS USM

Two more were added in 2008: the EF 800mm f/5.6 L IS and EF 200mm f/2 L IS.

The IS II series introduced in 2011-12 lacked the almost flat plate.

The major shift of weight to the rear and the resulting advantage of smaller elements began with the EF 400mm f/2.8 L IS III and EF 600mm f/4 L IS III in 2018.

Note that the EF 300mm f/2.8 L IS II, EF 400mm f/2.8 L IS II, EF 500mm f/4 L IS II, and EF 600mm f/4 L IS II, introduced in 2011-2012, other than removing the almost flat cover plate while also using fluorite for the second element as well as keeping the fluorite fourth element (fifth element in the older lenses with a protective plate), did not shift much of their optical formulae rearward. Their weight savings, which did not approach anywhere near the same degree of reduction as with the 2018 EF 400/2.8 IS III and EF 600/4 IS III, were as much a result of reducing the weight of non-optical components throughout the lens as they were of changes made to the optical formulae.

The 2011 EF 400mm f/2.8 L IS II (The 2011 EF 300mm f/2.8 L IS II was very similar):

Blueberry is fluorite

The 2018 EF 400mm f/2.8 L IS III:

Green is UD, purple is fluorite

The 1988 EF 600mm f/4 L:

Green is UD, purple is fluorite

The 1999 EF 600mm f/4 L IS:

Blue is UD, pink is fluorite

The 2012 EF 600mm f/4 L IS II (The EF 500mm f/4 L IS II was very similar):

Purple is fluorite

The 2018 EF 600mm f/4 L IS III:

Green is UD, purple is fluorite

AJ · Apr 14, 2026

DocInfoSci said:
With DLO the situation improves by leaps and bounds! It was DLO that kept the lens in my bag

Thanks! I'll give DLO a try on some of my old files.

Dragon · Apr 14, 2026

justaCanonuser said:
Due to a lack of time, I asked Perplexity (what I prefer since several years now over ChatGPT) why Nikon's Z system still offers AFMA and Canon's not, and explained in my prompt our specific AF problems with our Z8 & Z 600mm f/6.3 PF combo (with and w/o 1.4x TC). Perplexity's answer might be interesting for some nerds (like me) here:

Nikon Z cameras still offer AF fine-tuning because mirrorless autofocus is not automatically immune to optical tolerances. The camera can focus on the sensor plane very accurately, but a given camera/lens/teleconverter combination can still show small mechanical or optical offsets, especially when a teleconverter is added and the effective aperture gets smaller.[1][2]

Why the adjustment exists

The main reason is that focus accuracy is not just a software problem; it is also affected by lens design, manufacturing tolerances, adapter/teleconverter alignment, and how the camera interprets phase-detect data. Even in mirrorless, the system can be “close but not perfect” for a specific lens combination, so Nikon keeps fine-tune as a correction layer for edge cases and for users who need maximum precision.[3][2][1]

With long lenses, wide apertures, and teleconverters, the depth of field becomes very thin, so even a tiny offset looks like obvious backfocus or frontfocus. That is why a birding setup can seem fine in general use but still miss consistently on small distant subjects.[4][3]

Nikon vs Canon approach

Canon’s RF mirrorless system is generally more self-correcting in practice because Canon has leaned heavily on on-sensor phase detection and lens communication designed as a tightly integrated mirrorless platform. Nikon’s Z system also uses on-sensor phase detection, but Nikon still exposes AF fine-tune because it allows compensating for residual per-lens/per-body/per-converter variation rather than assuming every combination is perfect out of the box.[5][1]

The key difference is not simply “Canon has dual pixel, Nikon does not.” It is more about how each manufacturer implements lens-body calibration, predictive AF behavior, and tolerance management across the whole optical chain. Canon’s system tends to hide more of that from the user; Nikon gives the user a manual correction tool when the combination is off.[2][1]

Your specific setup

A Z8 plus Z 600mm f/6.3 PF plus TC 1.4x should normally focus well, so a “massive backfocus” points to an out-of-spec combination, a teleconverter/lens alignment issue, a body/lens calibration mismatch, or a focus-shift behavior that becomes visible only at the longer effective focal length and smaller maximum aperture. The fact that the issue appears both with and without the TC suggests the base lens/body calibration is already off, and the TC may be exaggerating it rather than causing it alone.[6][7][4]

Practical interpretation

So the short answer is: Nikon keeps micro-adjustment because mirrorless AF is not mathematically perfect for every optical combination, and Nikon chooses to let users compensate for residual system error. Canon’s RF system often feels more automatic because Canon’s implementation relies more on integrated on-sensor focusing and hides calibration differences better, but it is not because mirrorless AF fundamentally cannot need calibration.[1][5][2]

A useful rule of thumb is that if one Nikon Z lens or lens-plus-TC combo needs a large correction, that is usually a sign to test the lens, TC, and body separately, because the camera is compensating for a real mismatch rather than a normal tuning quirk.[8][6]

My personal conclusion: looks like we'd have to send this combo to Nikon's service because of too big production tolerances - typical Nikon's lousy quality, I have to say after many years of using Canon and Nikon gear side by side

The calibration for individual differences really doesn't make sense. Sensor PDAF is measuring at the point of focus so there should be no errors. If there is some residual error in the PD algorithm when concatenated with a particular lens, then fine tuning via CDAF on first use should clean that up and that may be what Canon is doing. An algorithm that starts from far OOF and tries to make it all the way in one shot clearly could have some issues, but with modern fast sensors, multiple focus checks as the lens motor is homing in seem logical. Contrary to the AI response, I would say Nikon has a software problem.

AlanF · Apr 14, 2026

Nemorino said:
The German names are more different: Common - Sandregenpfeifer and Little - Flußregenpfeifer.

Thank you, Alan! The R5m2 and the RF 200-800 is a good combo to catch them. And I had good luck as they have been close enough.
Some more!
R5m2 + Rf 200-800 + 1.4 TC
View attachment 228916 View attachment 228917 View attachment 228918 View attachment 228919

They are very sharp images considering their size and you were at 1120mm. Congratulations on excellent shots! Were you tracking them or could you use pre-capture?

Nemorino · Apr 14, 2026

ISv said:
In Germany you have two species of Ringed Plovers: the rare Common Ringed and the more often Little Ringed.

The German names are more different: Common - Sandregenpfeifer and Little - Flußregenpfeifer.

AlanF said:
Well done! Those Little Ringed Plovers move very fast.

Thank you, Alan! The R5m2 and the RF 200-800 is a good combo to catch them. And I had good luck as they have been close enough.
Some more!

R5m2 + Rf 200-800 + 1.4 TC

HeavyPiper · Apr 14, 2026

One from my old files with the EF 100-400mm L. Cropped.

neuroanatomist · Apr 14, 2026

justaCanonuser said:
...but my wife and I witnessed the murder of a mole (trigger warning: if you are too sensitive to the more brutal facts of life, don't scroll down).

Oh, that just looks like they're playing. This is also not with the EF 100-400L, but with its grandchild the RF 100-500L. Mr. Cooper doesn't play with his food.

"Hawk’s Prey"

EOS R3, RF 100-500mm f/4.5-7.1L IS USM @ 500mm, 1/250 s, f/7.1, ISO 12800

...and neither does his cousin, Red.

EOS 1D X, EF 70-200mm f/2.8L IS II USM @ 200mm, 1/80 s, f/2.8, ISO 320

Both of those were taken at my house.

justaCanonuser · Apr 14, 2026

I can't add here another tele zoom shot from the past days because I used always my 600 mm f/4.0 prime for birds, but my wife and I witnessed the murder of a mole (trigger warning: if you are too sensitive to the more brutal facts of life, don't scroll down). Unfortunately, the sun was already down behind the local trees, so there is no bright reflection spot in the killer's eye, but you can't order settings like this one for optimum conditions...

Storch mit Maulwurf Alte Fasanerie 04_06_2026.jpg

justaCanonuser · Apr 14, 2026

john1970 said:
A lightweight RF 500 mm f4 would be great as well and a nice surprise.

I bet that we never see again any new 500 mm f/4.0 prime from Canon! It wouldn't make sense since the 600mm f/4.0 lenses are so light now, and keeping two production lines that would cannibalize each other of such prime lenses wouldn't make sense economically.

Looking at Canon's recent strategy it is more probable that may see a new tele zoom covering the 500mm range in future what is faster than f/7.1 at the long end...

Michael Clark · Apr 14, 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

It was the only 300mm lens in Canon's catalog short enough to make it past security screening enforcing the "non-professional gear only" rules applied to ticket buying patrons (as opposed to someone with a media pass) at many major sports venues.

Michael Clark · Apr 14, 2026

AlanF said:
The Canon EF 600mm f/4 DO IS BR USM was first announced as a working prototype in September 2015 during the Canon Expo in New York. 11 years later still not here. That is genuine vaporware, announced and never marketed.

Did Chuck Westfall ever comment on the proposed EF 600mm f/4 DO IS BR USM?

justaCanonuser · Apr 14, 2026

AlanF said:
I used Reiken Focal for may years to AFMA DSLRs. They still produce their software for mirrorless, which is basically a waste of time for Canon as it just gives some limited information, but it does work with Nikon AFMA, and they explain why and the improvements. https://www.reikanfocal.com/why-nikon-mirrorless.html

It was very good indeed for DSLRs and I found it invaluable and the quickest and most accurate AFMA tool.

Thanks for this valuable tip, Alan. I called today the local Nikon service, they will check the combo, I have just to find a time slot to visit them. They promised they can do this service while I am waiting. Let's see what Nikon's experts tell us.

Michael Clark · Apr 14, 2026

Bob Howland said:
Often, the best way to end the conversation is to let the other party have the last word.

No it isn't!

Michael Clark · Apr 14, 2026

Del Paso said:
Friends!
When will we understand that it doesn't make sense to keep arguing with sect members, political fanatics, trolls or Sony fanboyz?
They never listen, convinced to be the beholders of Truth.
Let them keep their cute little tinfoil hats on and enjoy spreading their drivel !
If they have time to waste, let's not waste our time answering them.

But it has been so dead and boring in here for so long. Now there are posts and interactions and engagements. I'm sure that helps the bottom line of the site owners. If I had a site with not much in the way of new news to post, I might even be tempted to create a troll account in order to get things hopping for a while to pull up my engagement numbers and sell more ads...

Click · Apr 14, 2026

Nemorino said:
Somewhere I read Ringed Plover.

I really like the steep turn angle on the last one.

Click · Apr 14, 2026

I really like your shots. Beautiful pictures, ISv.

Marc73 · Apr 14, 2026

John D P said:
Since, the current 400 & 600 primes are EF lenses adapted to the RF mount; their due for a refresh. Before the world cup would make sense, but that doesn't mean they will do it.

As for a switchable teleconverter; I would prefer a completely separate unit. That way it can be used on other lenses and when it's needed. A built in teleconverter adds weight, length, and cost to the lens. I only need 1.4, not a fan of a 2.0 teleconverters ( my personal opinion). They have a working switchable teleconverter from the EF 200-400mm, that has shown reliability for years. Why haven't they adapted this into a separate teleconverter; there is no doubt in my mind it would sell. I would buy it. SEE DISCUSSION BELOW. I've learned you can't make a generic separate switchable teleconverter.

In my opinion, since the introduction of the RF mount Canon has put the long glass needs on the back burner. During this time, Sony & Nikon have developed better options and it's time for Canon to step up. The classic example is the gap between the 100-500mm and 400/600mm primes in the "L" series lenses. If you want upgrade to 600mm or faster glass from your 100-500, your ONLY option is a $13 to 14k prime. Then there is the mythical 300-600mm that has been teased for years. This would be a great wildlife lens, if their smart enough to make it a variable aperture of f4 to 5.6. For those of us that shoot in low light and want better bokeh; a fixed f5.6 aperture is unacceptable at the 300 to 400mm range for the anticipated price of at least 7K.

What about the 200-800mm?

Michael Clark · Apr 14, 2026

mimbu said:
Which is why Canon has blocked all 3rd party native glass from FF RF, and probably will do so in perpetuity.

Sigma's newer mirrorless native 150-600 is better optically than the EF glass while being less expensive, smaller, and lighter. Tamron's 150-500 is also excellent, and has extremely fast magnetic linear drive focus motors. (Sigma's 150-600 predates their magnetic linear AF, I expect their v2 will have that update.)

With no native RF competition, Canon can charge whatever they want for the 100-300/2.8 and 300-600/5.6. And they do/will.

Edit: For reference and comparison, the Sigma 150-600/5-6.3 DG DN OS Sports is US$875+tax here in Japan at the current exchange rate of USDJPY=159.

View attachment 228504

The Tamron 150-500/5-6.7 Di III VC VXD is US$737+tax:

View attachment 228505

These are the types of options that RF users miss out on because Canon does not believe in competition.

You're not taking the tariffs into consideration in addition to the exchange rates for anyone wanting to purchase them in the U.S.

Michael Clark · Apr 14, 2026

Del Paso said:
And I paid just a little more for the RF100-500 and it is definitely better than The Sigma 150-600...

Those 150-600mm Sigma lenses get noticeably progressively softer past around 300-350mm. At least in my limited experience and what I've seen my friends do with them.

Michael Clark · Apr 14, 2026

AlanF said:
Yeah, people think that a TC should have minimal copy variation because they are relatively simple and have no moving parts. But, I've tested a few in the past and found variation. My RF 2xTC seems good. I was worried about my RF 1.4x but it's the same as two others I've tried.

Yeah, you an take an EF 2X III that will be better on EF Super Telephoto Prime A than EF Super Telephoto Prime B with a different FL than Prime A, then take another copy of an EF 2X III that will be better on the same exact Prime B than the same exact Prime A. That's why the crying about "welding" a 2X onto a shorter lens and selling it as a 2X longer lens 2 stops slower is a bit of a red herring. In those cases they're designed to be optimized for that focal length and factory adjusted to the rest of that specific lens. Back in the early 2010s, the generally accepted wisdom was that the EF 2X was optimized for the EF 300/2.8 and wouldn't do quite as well on the 400/2.8, 500/2.8, etc. But you still had variation because of individual tolerance variation of both pieces when using them together.

AlanF · Apr 14, 2026

Ian K said:
It is yet to arrive, however I do agree, I couldn’t say no at that price. That said you do see grey imports on eBay for less, so I suspect they’re still making money.

Wex are as pukka a company as B&H in New York. They’re likely the largest camera retailer in the uk. They always have the stall right next to Canon every year. This year they had two stalls at the show. One next to Canon and another next to Nikon and Sony.

WEX is my favourite company - 100% reliable and never causes problems. You have got me thinking, and I'm going another route which is better for me and what I do. Most of my shots when birding are with the RF 200-800mm at 800mm, with occasional zooming out. I found it outresolves the 100-300 + 2xTC when set to 800mm and is at least as sharp at 600mm f/8. So, I will stick with that and to complement it I think I will definitely get an RF 70-200mm f2.8L IS USM Z as it much smaller than the 100-300 and a covers a more useful range at f/2.8 for me. For urban and indoor use, I prefer black, but for nature with the extender white. What a dilemma!

SteelLynx · Apr 14, 2026

Ah, thank you for that! I'll be on Vancouver Island in early June, and this makes me looking forward to it even more. If you happen to know some good spots, feel free to share

Del Paso · Apr 14, 2026

Chig said:
Yes from what I've seen in reviews, Jan Wegener (who's highly regarded in the bird photography world and one of my favourite You Tubers) has tested it and said it's very good with 2x https://youtu.be/DYBNX16zIhw?si=yTqtOfKQ3DbILnkC

Jan Wegener is one of the few reviewers I can take seriously.

AlanF · Apr 14, 2026

justaCanonuser said:
Due to a lack of time, I asked Perplexity (what I prefer since several years now over ChatGPT) why Nikon's Z system still offers AFMA and Canon's not, and explained in my prompt our specific AF problems with our Z8 & Z 600mm f/6.3 PF combo (with and w/o 1.4x TC). Perplexity's answer might be interesting for some nerds (like me) here:

Nikon Z cameras still offer AF fine-tuning because mirrorless autofocus is not automatically immune to optical tolerances. The camera can focus on the sensor plane very accurately, but a given camera/lens/teleconverter combination can still show small mechanical or optical offsets, especially when a teleconverter is added and the effective aperture gets smaller.[1][2]

Why the adjustment exists

The main reason is that focus accuracy is not just a software problem; it is also affected by lens design, manufacturing tolerances, adapter/teleconverter alignment, and how the camera interprets phase-detect data. Even in mirrorless, the system can be “close but not perfect” for a specific lens combination, so Nikon keeps fine-tune as a correction layer for edge cases and for users who need maximum precision.[3][2][1]

With long lenses, wide apertures, and teleconverters, the depth of field becomes very thin, so even a tiny offset looks like obvious backfocus or frontfocus. That is why a birding setup can seem fine in general use but still miss consistently on small distant subjects.[4][3]

Nikon vs Canon approach

Canon’s RF mirrorless system is generally more self-correcting in practice because Canon has leaned heavily on on-sensor phase detection and lens communication designed as a tightly integrated mirrorless platform. Nikon’s Z system also uses on-sensor phase detection, but Nikon still exposes AF fine-tune because it allows compensating for residual per-lens/per-body/per-converter variation rather than assuming every combination is perfect out of the box.[5][1]

The key difference is not simply “Canon has dual pixel, Nikon does not.” It is more about how each manufacturer implements lens-body calibration, predictive AF behavior, and tolerance management across the whole optical chain. Canon’s system tends to hide more of that from the user; Nikon gives the user a manual correction tool when the combination is off.[2][1]

Your specific setup

A Z8 plus Z 600mm f/6.3 PF plus TC 1.4x should normally focus well, so a “massive backfocus” points to an out-of-spec combination, a teleconverter/lens alignment issue, a body/lens calibration mismatch, or a focus-shift behavior that becomes visible only at the longer effective focal length and smaller maximum aperture. The fact that the issue appears both with and without the TC suggests the base lens/body calibration is already off, and the TC may be exaggerating it rather than causing it alone.[6][7][4]

Practical interpretation

So the short answer is: Nikon keeps micro-adjustment because mirrorless AF is not mathematically perfect for every optical combination, and Nikon chooses to let users compensate for residual system error. Canon’s RF system often feels more automatic because Canon’s implementation relies more on integrated on-sensor focusing and hides calibration differences better, but it is not because mirrorless AF fundamentally cannot need calibration.[1][5][2]

A useful rule of thumb is that if one Nikon Z lens or lens-plus-TC combo needs a large correction, that is usually a sign to test the lens, TC, and body separately, because the camera is compensating for a real mismatch rather than a normal tuning quirk.[8][6]

My personal conclusion: looks like we'd have to send this combo to Nikon's service because of too big production tolerances - typical Nikon's lousy quality, I have to say after many years of using Canon and Nikon gear side by side

I used Reiken Focal for may years to AFMA DSLRs. They still produce their software for mirrorless, which is basically a waste of time for Canon as it just gives some limited information, but it does work with Nikon AFMA, and they explain why and the improvements. https://www.reikanfocal.com/why-nikon-mirrorless.html

It was very good indeed for DSLRs and I found it invaluable and the quickest and most accurate AFMA tool.

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