Canon explains RF lens technology and why bigger is better (sometimes)

mjg79

EOS T7i
Feb 19, 2016
89
17
How many of your DLSR lenses cost $3K and up? I tend to believe that the Zeiss Otus lenses offer excellent IQ, equal of better to lenses with short flange distances. But like Leica ASPH lenses, they aren't cheap. The evidence definitely supports that more expensive lenses can deliver better IQ. But shorter flange? Not so much.
A fair question and it is quite a complex subject. Much of the debate on this area is a bit like arguing whether a V8 supercar is "better" than a V12. There's no exact answer even if one limits the analysis to just one or two areas - and in reality cars like cameras are complex pieces of technology where there will be various criteria.

If I had to summaries it simply I would say that while the throat opening of a mount doesn't have a huge impact though a wider opening, inevitably, will offer some slight advantages to a lens designer if one is looking for peak corner performance with wide aperture lenses and are happy to see the camera be physically bigger. Leica's M mount as well as Sony's FE shows that one can have high quality glass with a tight throat. Of perhaps more interest is the flange distance. This is where the biggest difference tends to show. All else being equal (that's a big 'if") a shorter flange distance will allow higher quality and smaller wide angle lenses. And that's about it. The impact of this is diminished by the reality of modern digital sensors. With film the difference was more pronounced.

At the end of the day though, good lens design is good lens design. If one wishes for a fast aperture, good corner performance, autofocus, IS etc well the lens likely will be large.

Looking at Sony we see from their lenses as well as from third parties that for 24mm and wider lenses there appear to be advantages. I've often been critical of Sony, their quality control in particular is abysmal, but they have some excellent lens designers from Minolta and Nikon now. And lenses like the 16-35 GM, 24 GM, Laowa 15/2, Sony 12-24/4 - all of these are theoretically superior - both in quality and also compactness - to an SLR lens. The advantage disappears very quickly. The Sony 35mm 1.4 ZA, aside from being one of the most badly built lenses in terms of quality control, isn't much smaller than an SLR lens. By 50mm the advantage seems to have completely disappeared in terms of size though it perhaps still affords a lens designer some ability to create higher grade optics. Perhaps - it's hard to say. And beyond 50 the question is pointless.

It's also part of a package. Note I say those lenses are theoretically better. I would far rather trust a Canon lens to be working and serviceable in 10 years for example and also to be built properly however we must acknowledge that the Sony 16-35 GM is in certain respects, especially size, a superior design to the 16-35L III. And in terms of ergonomics I think that a lens like a 70-200 or a fast 300 or 400mm lens will almost always balance better on a mount like the EF one than the FE or even R. The centre of gravity will simply be in a different spot.

Long term I actually think Canon is serious about maintaining EF mount cameras, especially for longer lenses. I think they are smart, for example, to make the RF 70-200L be extending and thus much smaller. I've used an A9 with the 70-200GM - the tech is great but the handling is quite unbalanced and certainly it doesn't feel as good to hold as a 1DX or 5D model with the Canon 70-200L. And the size difference is negligible. Perhaps the clearest example is the Sony 24-70GM - it's actually bigger than the Canon 24-70L and is very unbalanced on the Sony cameras.

Looking back I think many people overhyped mirrorless when it came to size and quality. There was an assumption we would end up with Leica M size and quality lenses with autofocus at reasonable prices. That was aways fantasy. In many ways I think the company that has come out best from this is Leica - I find myself with newfound admiration for their ability to make such high quality but small lenses - however they are simply willing to compromise in other areas - notably autofocus and price - that Canon, Sony and Nikon never would or could.

The answer has to be to not worry and to concentrate on photography. There are clearly a handful of use cases where mirrorless might offer some advantages but I feel the differences between systems are still far greater. I have been tempted by the A7R III with Loxia lenses for landscape photography, especially the 21mm/2.8 which shows a clear advantage over the Zeiss equivalent SLR lens in both optical quality and size. But it would mean giving up so much else that I like from Canon that I am unwilling to go. In time I will buy an R mount camera with their wide angle zoom which will almost certainly be better than the current 16-35L III and I will probably then adapt over most of my EF mount glass as it should work perfectly. Hopefully Zeiss and Voigtlander will make some small manual focus options for the R mount and we will be set. There will not be a small and high quality 24-70/2.8L or 35/1.4L, at least not if one wants autofocus and to not pay Leica money. That's life.

So which is better - the V8 or V12? It's entirely a subjective decision - do you prefer Ferrari or Lamborghini? Do you prefer Canon or Sony?
 
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neuroanatomist

I post too Much on Here!!
Jul 21, 2010
24,378
1,726
I don’t believe that Canon could make EF versions matching the RF 50 or RF 28-70 without adding size and weight. I don’t believe Sony could either, with their narrow APS-C designed FE mount.
The RF 50/1.2 is substantially bigger and heavier than the EF 50/1.2. Granted, it’s a different design...but optically similar to the Sigma 50/1.4A and Zeiss 50/1.4, both of which are smaller and lighter than the RF 50. So I’m pretty confident that Canon could easily make an EF 50/1.2 of similar size/weight to the RF version.

Agree that an EF 28-70/2 would be larger/heavier...but would it be enough of a difference to really matter for an already large and heavy lens? The fact that it’s 28mm instead of 24mm at the wide end suggests they were bumping up design limits.
 

neuroanatomist

I post too Much on Here!!
Jul 21, 2010
24,378
1,726
A fair question and it is quite a complex subject. Much of the debate on this area is a bit like arguing whether a V8 supercar is "better" than a V12. There's no exact answer even if one limits the analysis to just one or two areas - and in reality cars like cameras are complex pieces of technology where there will be various criteria.

If I had to summaries it simply I would say that the throat opening of a mount doesn't have a huge impact though a wider opening, inevitably, will offer some slight advantages to a lens designer if one is looking for peak corner performance with wide aperture lenses and are happy to see the camera be physically bigger. Leica's M mount as well as Sony's FE shows that one can have high quality glass with a tight throat. Of perhaps more interest is the flange distance. This is where the biggest difference tends to show. All else being equal (that's a big 'if") a shorter flange distance will allow higher quality and smaller wide angle lenses. And that's about it. The impact of this is diminished by the reality of modern digital sensors. With film the difference was more pronounced.

At the end of the day though, good lens design is good lens design. If one wishes for a fast aperture, good corner performance, autofocus, IS etc well the lens likely will be large.

Looking at Sony we see from their lenses as well as from third parties that for 24mm and wider lenses there appear to be advantages. I've often been critical of Sony, their quality control in particular is abysmal, but they have some excellent lens designers from Minolta and Nikon now. And lenses like the 16-35 GM, 24 GM, Laowa 15/2, Sony 12-24/4 - all of these are theoretically superior - both in quality and also compactness - to an SLR lens. The advantage disappears very quickly. The Sony 35mm 1.4 ZA, aside from being one of the most badly built lenses in terms of quality control, isn't much smaller than an SLR lens. By 50mm the advantage seems to have completely disappeared in terms of size though it perhaps still affords a lens designer some ability to create higher grade optics. Perhaps - it's hard to say. And beyond 50 the question is pointless.

It's also part of a package. Note I say those lenses are theoretically better. I would far rather trust a Canon lens to be working and serviceable in 10 years for example and also to be built properly however we must acknowledge that the Sony 16-35 GM is in certain respects, especially size, a superior design to the 16-35L III. And in terms of ergonomics I think that a lens like a 70-200 or a fast 300 or 400mm lens will almost always balance better on a mount like the EF one than the FE or even R. The centre of gravity will simply be in a different spot.

Long term I actually think Canon is serious about maintaining EF mount cameras, especially for longer lenses. I think they are smart, for example, to make the RF 70-200L be extending and thus much smaller. I've used an A9 with the 70-200GM - the tech is great but the handling is quite unbalanced and certainly it doesn't feel as good to hold as a 1DX or 5D model with the Canon 70-200L. And the size difference is negligible. Perhaps the clearest example is the Sony 24-70GM - it's actually bigger than the Canon 24-70L and is very unbalanced on the Sony cameras.

Looking back I think many people overhyped mirrorless when it came to size and quality. There was an assumption we would end up with Leica M size and quality lenses with autofocus at reasonable prices. That was aways fantasy. In many ways I think the company that has come out best from this is Leica - I find myself with newfound admiration for their ability to make such high quality but small lenses - however they are simply willing to compromise in other areas - notably autofocus and price - that Canon, Sony and Nikon never would or could.

The answer has to be to not worry and to concentrate on photography. There are clearly a handful of use cases where mirrorless might offer some advantages but I feel the differences between systems are still far greater. I have been tempted by the A7R III with Loxia lenses for landscape photography, especially the 21mm/2.8 which shows a clear advantage over the Zeiss equivalent SLR lens in both optical quality and size. But it would mean giving up so much else that I like from Canon that I am unwilling to go. In time I will buy an R mount camera with their wide angle zoom which will almost certainly be better than the current 16-35L III and I will probably then adapt over most of my EF mount glass as it should work perfectly. Hopefully Zeiss and Voigtlander will make some small manual focus options for the R mount and we will be set. There will not be a small and high quality 24-70/2.8L or 35/1.4L, at least not if one wants autofocus and to not pay Leica money. That's life.

So which is better - the V8 or V12? It's entirely a subjective decision - do you prefer Ferrari or Lamborghini? Do you prefer Canon or Sony?
To your point about corner performance, it’s interesting that the RF 50/1.2 is much larger and heavier than the EF version, but has stronger corner vignetting.

Totally agree with the basic premise that all of these modern camera systems are excellent and the real limiting factor, if there is one, is the person pressing the shutter release.
 

CanonFanBoy

EOS 5D MK IV
Jan 28, 2015
3,498
1,098
Irving, Texas
The contact area seems to protrude about the same distance into the mount on my R and 1D X. The no-mirror box on the R definitely looks spacious, though.
I've had to think that when Canon states "larger mount" they are speaking of a comparison between the Canon vs Sony vs Nikon mounts. That's the only way I can reconcile it myself. Right now, I am simply living vicariously through the rest of you who have already entered the world of R/RF. Exciting. As usual, I enjoy your input into the discussions. :)
 
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Normalnorm

EOS 7D MK II
Dec 25, 2012
502
105
I strongly disagree!
The old M lenses suffer, this is true, but the new ones are tack-sharp right into the edges. I do use them on Leica digital bodies, and I guarantee you, they are really sharp!
I noted that on ANY OTHER body than a Leica M.
Leica has engineered their microlenses for their lenses and thus have superb performance edge to edge on digital M bodies. On Other FF MILCs they suffer from edge smearing unless one modifies the body with a thinner cover glass. While getting better M lens performance one has now sacrificed native lens performance.
 

Larsskv

EOS 7D MK II
Jun 12, 2015
759
178
The RF 50/1.2 is substantially bigger and heavier than the EF 50/1.2. Granted, it’s a different design...but optically similar to the Sigma 50/1.4A and Zeiss 50/1.4, both of which are smaller and lighter than the RF 50. So I’m pretty confident that Canon could easily make an EF 50/1.2 of similar size/weight to the RF version.
The computer generated mtf charts of the Canon RF 50 (which unfortunately is my best source of information) indicates that it is better at f1.2 than either the Sigma 50 ART or the Zeiss 50 Milvus are at f1.4 (as measured by lens rentals).

The comparison tool at the digital picture shows they are close, but the difference in resolution in the comparison tool makes it hard to tell.

Roger Cicala states at the RF 50 L product page;

“Take a Zeiss Otus, make it accurately autofocus, and improve its optics a little. That’s how good it is.”

In my opinion the size/weight increase of the RF compared the ART and the Milvus is very small considering the half stop faster lens, indicating advantages to the RF mount.

Having owned the 50ART and owning the RF50, my opinion is that the RF 50 plays in a league of it’s own. Not necessarily in terms of sharpness, but especially in terms of bokeh and subject rendering. The RF 50 L gives me images that is razor sharp, with a look and feel to them that I would compare to the EF 50 L and EF 85 LII (which I love.)

The Sigma 50 ART images has a “sticker look to them. The subject that is in focus will often look like a sticker that has been added on a soft background. I couldn’t stand it and sold the Sigma after a couple of weeks after getting it.
 
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neuroanatomist

I post too Much on Here!!
Jul 21, 2010
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The computer generated mtf charts of the Canon RF 50 (which unfortunately is my best source of information) indicates that it is better at f1.2 than either the Sigma 50 ART or the Zeiss 50 Milvus are at f1.4 (as measured by lens rentals).

The comparison tool at the digital picture shows they are close, but the difference in resolution in the comparison tool makes it hard to tell.

Roger Cicala states at the RF 50 L product page;

“Take a Zeiss Otus, make it accurately autofocus, and improve its optics a little. That’s how good it is.”

In my opinion the size/weight increase of the RF compared the ART and the Milvus is very small considering the half stop faster lens, indicating advantages to the RF mount.

Having owned the 50ART and owning the RF50, my opinion is that the RF 50 plays in a league of it’s own. Not necessarily in terms of sharpness, but especially in terms of bokeh and subject rendering. The RF 50 L gives me images that is razor sharp, with a look and feel to them that I would compare to the EF 50 L and EF 85 LII (which I love.)

The Sigma 50 ART images has a “sticker look to them. The subject that is in focus will often look like a sticker that has been added on a soft background. I couldn’t stand it and sold the Sigma after a couple of weeks after getting it.
I think you’re reaching. Theoretical MTFs can’t be compared across manufacturers. The RF is a bit heavier, a bit better (although the vignetting is a bit worse), but it’s also a bit newer with newer coatings, etc. If the RF 50 is a good example of ‘benefit’ over lenses for the EF mount (and I’m not saying it is), that's a pretty weak argument.
 

3kramd5

EOS 5D MK IV
Mar 2, 2012
3,041
375
I think you’re reaching. Theoretical MTFs can’t be compared across manufacturers.
Agreed. Also Note that while Zeiss measures some sample of lenses for its published MTF, they do 10, 20, and 40 lp/mm; canon models 10 and 30, so there is only overlap in their contrast not resolution.

Lensrentals will likely measure the RF, and has measured the 11 copies of the Zeiss (at 10, 20, 30, 40, and 50 lp/mm).

185179
 
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MadisonMike

I'm New Here
May 30, 2019
10
8
I would also add this to the marketing idea. Consider the EF mount to Nikon way back in the day. Manufacturers know they’re going to be married to this mount for possibly 30 years. Do you think Canon is going to make the same mistake Nikon did or have the future in mind the same way they did when they developed the EF mount?

Nikon sure learned from their mistake and went with a drastically different mount for mirrorless. You can only get so far with creative marketing before you’re faced with the problem of physics.

The 28-70 f2 I would argue is made a practical lens because of the new mount. I’m not sure what’s not obvious about that.

I see that Sony plays on the ability to interchange lenses on crop and FF. That’s one way to market, but the reality is, their choice to use the same mount has crippled their ability to compete with Canon and Nikons mirrorless lenses. Especially as the market continues to shrink leaving pros and serious hobbyists who are going to expect faster zooms in a smaller package as we all strive to do more with less gear.
I don't see Sony crippled at all. The GM lenses are really nice. Having shot both formats I don't see that anyone is losing anything by using Sony glass. The sharing of mount configuration was a compromise for sure, but crippling no way. It may make it more difficult to design a lens but it can and is being done.
 

caffetin

EOS M50
Apr 20, 2019
35
12
Everything is OK with those lenses. I want to go with Canon r mount. But Thay are simply too expensive. I mean 3 basic lenses are close to new car.
 

FramerMCB

Canon 40D & 7D
Sep 9, 2014
376
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I don’t believe that Canon could make EF versions matching the RF 50 or RF 28-70 without adding size and weight. I don’t believe Sony could either, with their narrow APS-C designed FE mount.
I didn't address in any way how big and/or heavy EF versions of the 2 lenses I mentioned might have been. Only that Canon's Engineers probably could have designed them...
 

Larsskv

EOS 7D MK II
Jun 12, 2015
759
178
I didn't address in any way how big and/or heavy EF versions of the 2 lenses I mentioned might have been. Only that Canon's Engineers probably could have designed them...
The debate here, as I understand it, is whether or not the RF mount has advantages over the EF mount when it comes to lens design. In my opinion, all the RF lenses that has been released so far indicates similar or better optical quality in a smaller package, than the most comparable (aperture and quality wise) EF mount lens available.
 

mjg79

EOS T7i
Feb 19, 2016
89
17
To your point about corner performance, it’s interesting that the RF 50/1.2 is much larger and heavier than the EF version, but has stronger corner vignetting.

Totally agree with the basic premise that all of these modern camera systems are excellent and the real limiting factor, if there is one, is the person pressing the shutter release.
Indeed. Also re-reading what I wrote sounded like I was lecturing you, sorry if it came across like that, I was really using the way you had phrased that question as a springboard to a wider discussion.

The RF 50/1.2L is an interesting example really. In almost every respect it's optically "superior" to the EF 50/1.2L of course but much bigger. But the corner vignetting you point out really does suggest that factors beyond mount specification have a far bigger impact on a lens' performance. (The RF 35/1.8 suffers from a lot of vignetting too.) While I am sure certain aspects of mount specification do have some impact, the way people write about it recently has blown it out of all proportion. I am fairly sure that other factors such as how large the lens can be and the price point have far more impact - the Otus performance, even on Nikon's F-mount, shows what can be achieved.

One thought that strikes me through all of this is the long term importance of getting certain basic decisions right rather than agonising over a fraction of an inch here or there on the mount - and Canon really got it right that with the EF mount by going fully electronic. Which means I'l keep using my EF 50/1.2L on future R bodies seamlessly as for the things I use it for, almost exclusively portraits, it is perfect.
 
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mjg79

EOS T7i
Feb 19, 2016
89
17
I don't see Sony crippled at all. The GM lenses are really nice. Having shot both formats I don't see that anyone is losing anything by using Sony glass. The sharing of mount configuration was a compromise for sure, but crippling no way. It may make it more difficult to design a lens but it can and is being done.
I agree that it's silly to think Sony are crippled by this. The Leica M-mount is even narrower - whatever one thinks of Leica nobody would deny they have produced some amazing lenses.

And when people say it makes it easier to design lenses, well I am sure that's true for wide aperture lenses, though not that essential given things like the Leica Noctilux, but we must remember cameras and lenses form a package. I have often been highly critical of Sony but if one looks at an A7R with a Loxia 21, well it's hard to imagine a better small landscape set up. That wouldn't have been helped, indeed the body probably would have been made larger, by a wider diameter mount.
 

Architect1776

Defining the poetics of space through Architecture
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The RP gives hope that some less expensive lenses may show up, as does the RF 35 f1.8. However these lenses are likely to be larger than an EFS 10-18. A lens equivalent to an EFS 10-18 that would cover a FF sensor would be 16-29. Even with variable maximum aperture this would be a larger and likely more expensive lens than the 10-18. For EF-S and EF-M size and prices, APS-C sized sensor coverage is part of the deal.
I guess I look at the manual Olympus lenses of yore. They had the same parameters of distance, mirror box and FF format, yet for some reason were able to be made relatively small. They were all metal and well built with superb optics too. Just wondering what the problem is today? Yes adding AF does increase the size but that much?
 
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BillB

EOS 6D MK II
May 11, 2017
1,056
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I guess I look at the manual Olympus lenses of yore. They had the same parameters of distance, mirror box and FF format, yet for some reason were able to be made relatively small. They were all metal and well built with superb optics too. Just wondering what the problem is today? Yes adding AF does increase the size but that much?
AF does increase the size of the lenses, as do faster apertures. There are a lot more electronics and moving parts in a modern lens. Also, you did not see a lot of 24-105, 16-35 or 70-200 zooms back in the day, so people had to make do with manual primes. Because people can choose modern good quality zooms, the market for primes has been a shrinking part of a shrinking market for a while now.

One of the first RF lenses that Canon released was the 35mm f1.8, which is probably as small as you are going to get these days. The cost of the 35mm is nearly half that of the 24-105, and it weighs a little less than half as much. So, if you buy a second prime (say an EF 85 f1.8 that you will adapt), your will be spending about the same as for the 24-105, and the two primes together will weigh nearly as much as the zoom. For a lot of people, the value proposition for a zoom looks pretty good.

The RF 35 makes a lot sense to me, and apparently it made sense to Canon as well. However, as far as small, reasonably priced primes are concerned, I am not sure where it goes from here. An 85mm? Something in the low 20's? We shall see.
 

mjg79

EOS T7i
Feb 19, 2016
89
17
I guess I look at the manual Olympus lenses of yore. They had the same parameters of distance, mirror box and FF format, yet for some reason were able to be made relatively small. They were all metal and well built with superb optics too. Just wondering what the problem is today? Yes adding AF does increase the size but that much?
I have had little experience with those old Olympus lenses though have sometimes examined them in second hand shops and they always felt like very nice, high quality lenses. I have a lot of respect for Olympus and have a friend who has been around the world with various m4/3 cameras from them - he's the type who goes trekking through rainforests and across deserts and he swears by Olympus. The thought has often occurred to me that Canon and Nikon were lucky that it was Sony - with all their problems with quality control and sometimes strange (and sometimes brilliant) approaches - who challenged them in the full frame market - imagine had Olympus had the funds to have built the A7 series, how polished, how functional, how much better frankly it would have been. So I have no desire to run down Olympus but were those OM lenses really on a par optically with modern lenses?

I personally think it's all gone a bit mad in recent years with everyone obsessing over how sharp every f/1.4 lens is in the corners wide open. It seems pretty clear to me that this has driven lenses getting ever larger. The 35L for example was a very high quality lens but a desire for it to be better corrected and sharper in the corners made the Mark II bigger. It's an approach Sigma took with their Art lenses and Zeiss with their Otus lenses. From what I have read the latter work quite well on some medium format sensors - they took that, one might almost say, crude approach to getting good corners.

I actually think there will be some market for lenses that are not exactly perfect. Voigtlander seems to have spotted this - their 40/1.2, 50/1.2 and 21/3.5 are all lacking the amazing MTFs of lenses like Otuses but they are small and full of character. Leica has started to make lenses a bit bigger than in the past though they are still tiny compared to most but even they can't change the laws of physics. The Summilux-M 35, for example, is in most measurable senses, inferior to the larger (by rangefinder standards) Zeiss 35/1.4 ZM. However I've used both and can say though the Summilux has to my eyes a nicer rendering and the fact it is smaller appeals to me over the extreme corner sharpness at f/1.4 of the ZM.

So "imperfect" lenses can represent a nice trade off with size and weight if one accepts corners at f/1.4 might not be perfect. Furthermore it often seems the case that less corrected lenses have a nicer rendering - I don't think I am alone in being unmoved by the RF 50/1.2L - it's a technical marvel, no doubt, but for photographing people, holds no appeal over the EF 50/1.2L for me.

So I'm really not saying the classic lenses are rubbish but I think we often have some rose tinted spectacles in assuming the smaller and jewel-like, built of metal, lenses of the 70s and 80s were as good optically as today's monster lenses. Nicer to hold? Definitely. A nicer rendering? Sometimes. But able to survive a hundred review websites screaming that the corner isn't perfectly sharp wide open? I think Voigtlander, Leica and Zeiss can get away with that but for the big manufacturers it is something they fear.
 
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Architect1776

Defining the poetics of space through Architecture
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I have had little experience with those old Olympus lenses though have sometimes examined them in second hand shops and they always felt like very nice, high quality lenses. I have a lot of respect for Olympus and have a friend who has been around the world with various m4/3 cameras from them - he's the type who goes trekking through rainforests and across deserts and he swears by Olympus. The thought has often occurred to me that Canon and Nikon were lucky that it was Sony - with all their problems with quality control and sometimes strange (and sometimes brilliant) approaches - who challenged them in the full frame market - imagine had Olympus had the funds to have built the A7 series, how polished, how functional, how much better frankly it would have been. So I have no desire to run down Olympus but were those OM lenses really on a par optically with modern lenses?

I personally think it's all gone a bit mad in recent years with everyone obsessing over how sharp every f/1.4 lens is in the corners wide open. It seems pretty clear to me that this has driven lenses getting ever larger. The 35L for example was a very high quality lens but a desire for it to be better corrected and sharper in the corners made the Mark II bigger. It's an approach Sigma took with their Art lenses and Zeiss with their Otus lenses. From what I have read the latter work quite well on some medium format sensors - they took that, one might almost say, crude approach to getting good corners.

I actually think there will be some market for lenses that are not exactly perfect. Voigtlander seems to have spotted this - their 40/1.2, 50/1.2 and 21/3.5 are all lacking the amazing MTFs of lenses like Otuses but they are small and full of character. Leica has started to make lenses a bit bigger than in the past though they are still tiny compared to most but even they can't change the laws of physics. The Summilux-M 35, for example, is in most measurable senses, inferior to the larger (by rangefinder standards) Zeiss 35/1.4 ZM. However I've used both and can say though the Summilux has to my eyes a nicer rendering and the fact it is smaller appeals to me over the extreme corner sharpness at f/1.4 of the ZM.

So "imperfect" lenses can represent a nice trade off with size and weight if one accepts corners at f/1.4 might not be perfect. Furthermore it often seems the case that less corrected lenses have a nicer rendering - I don't think I am alone in being unmoved by the RF 50/1.2L - it's a technical marvel, no doubt, but for photographing people, holds no appeal over the EF 50/1.2L for me.

So I'm really not saying the classic lenses are rubbish but I think we often have some rose tinted spectacles in assuming the smaller and jewel-like, built of metal, lenses of the 70s and 80s were as good optically as today's monster lenses. Nicer to hold? Definitely. A nicer rendering? Sometimes. But able to survive a hundred review websites screaming that the corner isn't perfectly sharp wide open? I think Voigtlander, Leica and Zeiss can get away with that but for the big manufacturers it is something they fear.
Digital created the pixel peeping clowns at 100% + that we photographers have to suffer with. At realistic viewing distances no one can tell the difference between a cheap or a most expensive lens, unless there is actually something wrong with the cheap lens.