Latest activity

Michael Clark · Apr 15, 2026

Bob Howland said:
Update: My point is that the DOF of a lens is entirely independent of the size of the sensor which receives its image.

Except it's not unless you enlarge images from all sensors by the same factor and your FF images are thus 1.6X larger than your APS-C image. If you enlarge images from differently sized sensors to the same display size, you enlarge the smaller images by a greater factor, thus enlarging the blur in those images by a greater factor. Some blur that is not perceptible as blur at a smaller enlargement factor will be perceptible as blur at the higher enlargement factor.

If you take the same exact digital file and view it at two different display sizes from the same distance, the DoF changes! You can even view the same displayed image from two different distances and the DoF changes!

Two things determine Depth of Field: aperture and total magnification. The lens only fully controls one of those factors. Total magnification is determined by subject distance, focal length, the enlargement ratio from the image size projected onto the sensor to the image size as displayed when viewed, the viewing distance from the displayed image to the viewers eyes, and even the viewer's visual acuity which determines the smallest arcminute (under near ideal lighting conditions for a person with 20/20 vision the limit is right at 1 arcminute) or arcseconds of angle that is perceivable as blur.

Michael Clark · Apr 15, 2026

dwkdnvr said:
Thinking more about the 15-70/4, I find it somewhat interesting that it's not quite a direct head-to-head competitor to either of the Sigma normal zooms, but that the Tamron 17-70 IS which IS a bit more of a direct competitor never appeared for RF-S. Makes me wonder whether Canon did actively prevent Tamron from offering that lens in RF-S mount.

I still wish this would have L-grade construction, but it seems far more likely that it'll be on the level of the budget FF STM lenses.

InternalRevenue said:
The absence of the 17-70 does indeed make more sense now, that was Tamron’s only mirrorless APS-C lens that didn’t directly compete against a superior Sigma alternative on RF mount, and one that would’ve been popular with the RF-S bodies lacking IBIS (4/5 currently).

If the construction isn’t L caliber, I hope it’s at least along the lines of the RF 28-70 f/2.8.

Things that make you go, "Hmmmm?"

Michael Clark · Apr 15, 2026

zapper said:
Yes. For complex lenses, the entrance pupil may be very different than the front element size. I'm fuzzy on the relationship; this is what Google tells me: "The entrance pupil in a complex lens is determined by imaging the physical aperture stop through all preceding optical elements into object space. It is the virtual or real image of the diaphragm as seen from the front of the lens, defining the cone of light that enters the system."

Of course. And field of view depends on the focal length and the sensor size.

At narrow angles of view (i.e. telephoto lenses) the EP and the front element are pretty much the same size, give or take 10% or less. It's wider angle lenses where the EP is a virtual image often located well behind the physical aperture diaphragm.

Michael Clark · Apr 15, 2026

dwkdnvr said:
*IF* this lens has any degree of weather sealing it would solve the lens dilemma I've been struggling with and will be an insta-buy for me. But this is RF-S so I'm fully expecting that it will continue the budget build quality tradition. It will definitely cause me to wait and see whether it pans out before going with another option, though.

Coming from the M43 world I didn't entirely realize how spoiled they are for hiking/travel lenses. All sorts of 24-xx (equivalent) options many with robust build and weather sealing at a range of aperture/size/cost. I'm trying to find 'that lens' for my R7. Maybe I'm over-valuing weather resistance, but being in the dusty SW and having been caught in weather when traveling far too frequently I'm far more comfortable having it. (we got drenched several times on a trip to NZ and the E-M1.2/12-100 came through with aplomb)

The only RF-S lens with any advertisement of splash/dust resistance is the Sigma 17-40 which is probably the most logical choice, but I'm unreasonably annoyed that it's 17 rather than 15 on the wide end. And general hiking/travel really doesn't need F/1.8 so there's a size penalty. I find myself very seriously considering the RF 14-35/4 as it seems the best fit - 22-56 equivalent (maybe even a bit wider if you manually tweak the corrections), L build quality, reportedly great optically even with the corrections (and APS-C avoids the worst of the corrections in the first place); just evaluating whether paying the premium for an FF ultra-wide (albeit a fairly reasonably priced one) is worth it.

Weather resistance is pretty easy to do fairly cheaply. I've used the same two OP/TECH rain covers dozens of times over the past 15+ years. I can't believe they've held up so well. I figured they would be more or less disposable. I think I have another bag or two of them socked away somewhere in the house, but I've not yet needed to replace the two in my camera bag. I have used a cheaper no-name brand with room for a flash and they do tend to tear sometimes.

I've shot field sports in all kinds of weather, and community parades in downpours. I have yet to have any issues with any of my gear due to water or dust.

Michael Clark · Apr 15, 2026

Tom R5R7 said:
Yeah, even on in the 10D says, 17 was tight. But the standard "kit" lens 18 was even tighter. And for all the concerns about deficiencies, its f/4 aperture was pretty useful. F/2.8 would have been better, but the 16-35 f/2.8 at the time was really not quite as good a lens. it had some really crazy flare issues.

I've had an EF 17-40mm f/4 L since around 2011. It also likes to flare and ghost if there are bright specular highlights, such as stadium light towers, in the frame. I've never used it on APS-C, though, only on FF. If I was using an APS-C body at the same time the APS-C always had the EF 70-200mm f/2.8 L IS II on it.

In my experience the EF 17-40mm f/4 L was sharper at f/4 than the EF 16-35mm f/2.8 L and the EF 16-35mm f/2.8 L II at f/4, but nowhere near as sharp at f/4 as the later EF 16-35mm f/4 L IS. As camera resolutions have increased and newer lenses with better acutance have emerged, such as the (admittedly considerably more expensive) EF 16-35mm f/2.8 L III, it's not quite the useful lens it once was.

Michael Clark · Apr 15, 2026

Aldherrian said:
The lack of such a lens made me upgrade to FF format but I'm glad some stuff is finally happening to the APSC side

Perhaps that's why Canon quit making f/2.8 APS-C zoom lenses?

Michael Clark · Apr 15, 2026

neuroanatomist said:
It doesn’t scale like that, as @AlanF stated. For example, my RF 100-400mm f/8 has a front element of ~50 mm in diameter. 400 mm / 8 = 50 mm. So far so good.

If that relationship scaled across all focal lengths, my RF 10-20mm f/4 would have a front element of ~5 mm in diameter. In fact, its front element is ~60 mm in diameter, larger than that of the 100-400/8.

That's because the entrance pupil for wide angle lenses is not at the front, it's generally behind the aperture diaphragm. If a 20mm f/4 lens only had a 5mm diameter, it would SEVERELY vignette. A subject on the edge of the field of view must be able to "see" the edge of the entrance pupil.

When the edge of the FoV is blocked from seeing the entire EP, we get "cat's eye" bokeh and vignetting. At smaller apertures the angles are not as severe and the entire EP can be seen from the same point on the edge of the FoV.

Michael Clark · Apr 15, 2026

neuroanatomist said:
Regardless, having a battle of wits with an unarmed opponent is pointless. I'm out.

Promises, promises...

Michael Clark · Apr 15, 2026

Bob Howland said:
It's not f/6.3. It's a 15-70 f/4 lens with the DOF of a 15-70 f/4 lens, regardless of the size of sensor. The only reason the DOF changes is when people move forward or back or change the focal length to maintain the same FOV. I'm rather interested in this lens but I already own the 18-50 Sigma and I highly value small size and especially light weight.

Differences in magnification ratio to get the same viewing size from disparately sized sensors also affect Depth of Field, but not in the direction most people think. When you have to magnify more to get the same display size from a smaller sensor, you magnify everything, including blur more. Magnifying blur by a greater amount decreases depth of field.

Michael Clark · Apr 15, 2026

Salamander said:
I currently have the R6ii with the RF 24-105 f4-7.1 lens. I’m considering getting the RF 24-70 f2.8. I know the 2.8 will be better in low light. I’m curious if there is much difference in the quality of pictures taken outside in daylight, particularly as you zoom towards 70mm.

The constant aperture f/2.8 obviously also gives you the option to shoot at wider apertures in brighter light if your camera can shorten exposure times enough to compensate or if you use Neutral Density filters. The minimum exposure time of the R6 Mark II is 1/8,000 with mechanical shutter and 1/16,000 with electronic shutter. "Sunny 16" gives you ISO 100, f/2.8 at 1/6,400.

Michael Clark · Apr 14, 2026

Dragon said:
That all makes perfect sense but doesn't address the idea that the system should be able to tweak the goal on the fly since it has access to many samples as the lens is focusing. I see no reason why mirrorless PDAF can't work similarly to CDAF with the exception that it should be able to avoid overshoot and hunting because it inherently knows whether the instant focus is front or back and CDAF does not. If the lens motor does overshoot, the system should still be able to back it up in no more than one extra try. I still think Nikon has some software optimization to do if the previous comments are correct. That said, I have a Tamron 18-400 that won't focus precisely at the long end on any body (SLR or Mirrorless). The Tap-In console has no effect when uses on a DPAF mirrorless body, and manual focus notably better than AF. Interestingly it comes very close to correct focus when used on a 5DSR in live view mode. That camera uses CDAF in live view, which would suggest that even Canon does not iterate focus attempts as much with DPAF as is does with the CDAF in the 5DSR. It also suggests that Tamron didn't get even the EF focus algorithm quite right. Their response when questioned was a request to send the lens and the camera body to them for fine tuning (but ironically, the Tap In fine tuning has no effect) but that doesn't make the lens universal as it would only match it to one body if successful. Since I don't have that much use for the lens in RF land, I demurred. As an aside, you would think if the problem is overshoot, hitting the half press on the shutter button a second time would improve the focus, but it does not. So maybe the Nikon tweak will be more compatible with 3rd party lenses that don't quite follow the instructions they are given. It would be an interesting test if someone has a copy of that lens in Nikon format.

Except while all of this focusing and refocusing is going on the subject is often moving erratically and changing the distance between subject and camera. There aren't many use cases for still life photography with Super Telephoto lenses. And the camera's processor(s) needs significantly more processing cycles to predict where that moving subject will be when the shutter actuates than it needs to perform a focus measurement.

With DSLRs Canon placed a higher priority on speed when using the optical VF with dedicated PDAF array, and a higher priority on accuracy when using Live View with main sensor based DPAF.

Michael Clark · 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

It seems to me that with MILCs the issue is usually how accurately the lens can move compared to how much the camera told the lens to move, and how well the camera can know how much the lens actually moved without continuing to focus during the movement when processing cycles might be better spent for predictive analysis of where the target will be when the shutter (mechanical or electronic) is actuated. Move and refocus is much slower than measure focus, tell the lens which way to move and how far, then confirm the lens has moved that far without measuring focus again, and take the picture.

As others have also pointed out above, not all lenses hold an exact focus position once the AF motor stops moving it, either. Wear and tear leaves room for "play", just like an older car has more steering wheel play than when it was new. If you stop turning the wheel to the right and start turning it back to the left, you have to move it an inch or a few before the movement of the steering wheel starts turning the tires in the opposite direction.

Doing AFMA calibration for friends, I've seen cases where the correction need to be slightly different depending on if the lens started out towards MFD or towards infinity before AF was actuated.

Dragon · Apr 14, 2026

AlanF said:
Here is what a another AI engine writes:

Why the Feature Still Exists
If the path error is gone, why did Nikon keep the menu option in the Z6, Z7, Z8, and Z9? It comes down to Phase Detection (PDAF) vs. Contrast Detection (CDAF).

PDAF is a "Predictor": Most Nikon Z cameras use on-sensor Phase Detection. PDAF works by looking at two different views of the subject and calculating exactly how far the lens needs to move. It’s incredibly fast, but it is technically an open-loop calculation.

Manufacturing Tolerances: Even with on-sensor PDAF, slight variances in how a specific lens's motor reacts to a command can exist. While the camera should see that it's in focus, the PDAF algorithm might consistently stop the lens a tiny bit short or long due to the lens's specific mechanical behavior.

Spherical Aberration (Focus Shift): Some lenses shift their focus point slightly as you close the aperture (stop down). Since cameras usually focus with the lens wide open, the "perfect" focus point at f/1.8 might be slightly different than at f/2.8. AF Fine-Tune allows a pro to "offset" this shift for their most-used aperture.

3. Using Adapted F-Mount Lenses
The most practical reason Nikon kept AF Fine-Tune is the FTZ Adapter. Many photographers use older DSLR (F-mount) lenses on their mirrorless bodies.

These older lenses were designed for the mechanical "tug-of-war" of DSLR systems.

While the mirrorless sensor is more accurate, some older lens motors may not "settle" perfectly on the target when driven by the new mirrorless algorithms.

If you find your favorite 85mm f/1.4 G lens is always just a hair soft on your Z8, the AF Fine-Tune lets you bridge that gap.

That all makes perfect sense but doesn't address the idea that the system should be able to tweak the goal on the fly since it has access to many samples as the lens is focusing. I see no reason why mirrorless PDAF can't work similarly to CDAF with the exception that it should be able to avoid overshoot and hunting because it inherently knows whether the instant focus is front or back and CDAF does not. If the lens motor does overshoot, the system should still be able to back it up in no more than one extra try. I still think Nikon has some software optimization to do if the previous comments are correct. That said, I have a Tamron 18-400 that won't focus precisely at the long end on any body (SLR or Mirrorless). The Tap-In console has no effect when uses on a DPAF mirrorless body, and manual focus notably better than AF. Interestingly it comes very close to correct focus when used on a 5DSR in live view mode. That camera uses CDAF in live view, which would suggest that even Canon does not iterate focus attempts as much with DPAF as is does with the CDAF in the 5DSR. It also suggests that Tamron didn't get even the EF focus algorithm quite right. Their response when questioned was a request to send the lens and the camera body to them for fine tuning (but ironically, the Tap In fine tuning has no effect) but that doesn't make the lens universal as it would only match it to one body if successful. Since I don't have that much use for the lens in RF land, I demurred. As an aside, you would think if the problem is overshoot, hitting the half press on the shutter button a second time would improve the focus, but it does not. So maybe the Nikon tweak will be more compatible with 3rd party lenses that don't quite follow the instructions they are given. It would be an interesting test if someone has a copy of that lens in Nikon format.

Michael Clark · Apr 14, 2026

justaCanonuser said:
The symptoms with the Z8 and the Z 600/6.3 are: the camera focuses fast (with no TC attached) and gets in particular very close to in-focus images with the first frame(s), but then starts to struggle with following frames, and the AF sort of micro-pumps around the precise focus position.

That sounds like the original 7D in AI Servo mode.

ISv · Apr 14, 2026

AlanF said:
By coincidence I've been studying these for the past week. There's a new fenced off area with a flood close by, and 2 pairs of Little Ringed Plovers have been scurrying around, usually about 80-100m away. On Friday, a pair was on the near side, only some 80m away, and I got an adequate shot of one - in which the bird is only 330 px long with the RF 200-800mm on the R5ii. It does show clearly the eye ring.
and the beak. I posted it on one of the gear threads so here it is again. Yesterday, as they were far away again I had to use the 1.4x on the lens to get to 1120mm, and actually got one flying off from the other. They are ridiculously small but good enough for my records.

View attachment 228900 View attachment 228901

To make the things little bit more complicated

: Semipalmated plover (Charadrius semipalmatus). Non breeding plumage.

ISv · 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

So it's "Regen river Plover"

. I suspect you are not chasing them around Regen river...

neuroanatomist · Apr 14, 2026

Depends on what you mean by supported. CFe v4 work fine, but Canon bodies only support v2 speeds. I have a set of Prograde v4 cards (3 x 256 GB, 2 x 1 TB) that I use with my R1. The faster speed means copying files to my Mac is fast, but slower cards would not be a bottleneck for the camera.

ronbyram · Apr 14, 2026

Hello Gang,
I am a R6 Mark II owner but I am thinking about moving up to either the Mark III and or R5 or a used R1 for my sport photography.
Does anyone recomend a brand and or size.

Does anyone know if the 4.0 format is supported? I know Memory is high $ but wanted to ask.

I currently use Prograde 256 cards on my Mark II

justaCanonuser · Apr 14, 2026

neuroanatomist said:
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"
View attachment 228907
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.

View attachment 228908
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.

great images! You have nice neighbors (as long as you aren't commenting from a prey's viewpoint).

In fact, the stork finally swallowed the mole, after he stabbed the poor guy several times with and afterwards flattened him with his beak.

justaCanonuser · Apr 14, 2026

AlanF said:
Here is what a another AI engine writes:

Manufacturing Tolerances: Even with on-sensor PDAF, slight variances in how a specific lens's motor reacts to a command can exist. While the camera should see that it's in focus, the PDAF algorithm might consistently stop the lens a tiny bit short or long due to the lens's specific mechanical behavior.

This describes what we observe so far most exactly. We did not yet adapt any older F mount lens, and I could not yet find any reliable information about a possible focus shift of this Z 600mm f/6.3 PF lens. Thanks for your kind help, Alan!

justaCanonuser · Apr 14, 2026

Dragon said:
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.

We'll hopefully find out via Nikon service what's the problem. But, based on our experience with a Nikon gear side by side by a comparable Canon gear I can only wrap up: Nikon has severe quality problems in the past 15 years anyway. Based on all the various failures that happened with our Nikon gear I wouldn't recommend to change from Canon to Nikon.

AlanF · Apr 14, 2026

Dragon said:
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.

Here is what a another AI engine writes:

Why the Feature Still Exists

If the path error is gone, why did Nikon keep the menu option in the Z6, Z7, Z8, and Z9? It comes down to Phase Detection (PDAF) vs. Contrast Detection (CDAF).

PDAF is a "Predictor": Most Nikon Z cameras use on-sensor Phase Detection. PDAF works by looking at two different views of the subject and calculating exactly how far the lens needs to move. It’s incredibly fast, but it is technically an open-loop calculation.
Manufacturing Tolerances: Even with on-sensor PDAF, slight variances in how a specific lens's motor reacts to a command can exist. While the camera should see that it's in focus, the PDAF algorithm might consistently stop the lens a tiny bit short or long due to the lens's specific mechanical behavior.
Spherical Aberration (Focus Shift): Some lenses shift their focus point slightly as you close the aperture (stop down). Since cameras usually focus with the lens wide open, the "perfect" focus point at f/1.8 might be slightly different than at f/2.8. AF Fine-Tune allows a pro to "offset" this shift for their most-used aperture.

3. Using Adapted F-Mount Lenses

The most practical reason Nikon kept AF Fine-Tune is the FTZ Adapter. Many photographers use older DSLR (F-mount) lenses on their mirrorless bodies.

These older lenses were designed for the mechanical "tug-of-war" of DSLR systems.
While the mirrorless sensor is more accurate, some older lens motors may not "settle" perfectly on the target when driven by the new mirrorless algorithms.
If you find your favorite 85mm f/1.4 G lens is always just a hair soft on your Z8, the AF Fine-Tune lets you bridge that gap.

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):