jaapv Posted January 17, 2016 Share #141 Posted January 17, 2016 Advertisement (gone after registration) A planparallel surface shortly behind the lens, yes, but I doubt whether a cover glass near the plane of focus makes any difference to the design. As for the size, maybe, but modern Leica M lens designs are still pretty compact. Link to post Share on other sites More sharing options...
Advertisement Posted January 17, 2016 Posted January 17, 2016 Hi jaapv, Take a look here Rumor - Three new Leica M lenses tomorrow?. I'm sure you'll find what you were looking for!
CheshireCat Posted January 17, 2016 Share #142 Posted January 17, 2016 Optimized for digital means that the optical formula has been tweaked to neutralize the astigmatism in the image periphery caused by the cover glass. Note that my post about the cover glass was just speculation. Are you sure about this ? Source ? Link to post Share on other sites More sharing options...
edwardkaraa Posted January 17, 2016 Share #143 Posted January 17, 2016 Note that my post about the cover glass was just speculation. Are you sure about this ? Source ? Educated guess based on Leica statement and size changes. Anyhow I'm just explaining what optimized for digital means, no matter the manufacturer. The designer has to take the cover glass thickness into account. Link to post Share on other sites More sharing options...
Herr Barnack Posted January 17, 2016 Share #144 Posted January 17, 2016 I'll never, ever, buy another frigging Leica lens: - 28mm Summicon: the plastic bit at the front of the lens fell out. Not a big deal but tacky given the price. - 24mm Elmar: bought just before Xmas; wouldn't focus on infinity. Schmidt in Hong Kong said they needed to send it back to Germany for a few weeks. Instead, I found a local technician who fixed it for free in a few minutes - 21mm SEM: the aperture ring became so loose that I could almost blow it around. This is a lens thread so I won't mention the rangefinder issue with a brand new M9, another issue with my 2nd M9, or Leica dishonouring the warranty on my Q. Fuji beckons..... Since the three M lenses you speak of are of such slipshod quality and are so frustrating to use, I am willing to be of assistance in freeing you from these abominations. I am willing to offer you as much as $500 USD for the three, and I will cover shipping costs. This way, you will be shed of these infuriating pieces of junk and will be able to make the transition to the Fuji system unfettered by Leica's inferior M lenses. I will of course then be forced to bear the cost of shipping all three lenses to Wetzlar to have them made right; this will be an inconvenience on my part as well as a significant sacrifice financially, but it is a cross I am willing to bear in order to be of service to a fellow photographer. Link to post Share on other sites More sharing options...
wlaidlaw Posted January 17, 2016 Share #145 Posted January 17, 2016 Since the three M lenses you speak of are of such slipshod quality and are so frustrating to use, I am willing to be of assistance in freeing you from these abominations. I am willing to offer you as much as $500 USD for the three, and I will cover shipping costs. This way, you will be shed of these infuriating pieces of junk and will be able to make the transition to the Fuji system unfettered by Leica's inferior M lenses. I will of course then be forced to bear the cost of shipping all three lenses to Wetzlar to have them made right; this will be an inconvenience on my part as well as a significant sacrifice financially, but it is a cross I am willing to bear in order to be of service to a fellow photographer. That could be characterised as "rubbing salt into the wound" Link to post Share on other sites More sharing options...
Rick Posted January 17, 2016 Author Share #146 Posted January 17, 2016 So, does this presage a thicker cover glass for the new M? Is the release of these new wide lens designs in preparation for the next M with a thicker cover glass, in order to get better color? Maybe, in the end it is easier to redesign lenses than to continue down the micro-mirror, thin-edge cover glass road. It certainly would be more profitable to change the designs of the wides, especially the most offending ones (28 Summicron). The new 28 Summilux certainly was not designed for the sensor edges of the M240. It was probably designed for the new M? Rick Link to post Share on other sites More sharing options...
semi-ambivalent Posted January 17, 2016 Share #147 Posted January 17, 2016 Advertisement (gone after registration) Note that my post about the cover glass was just speculation. Are you sure about this ? Source ? I think it's a pretty good speculation. If a light ray strikes a glass surface at less than ninety degrees it is refracted by some amount and is refracted again by some amount when exiting the other side. This must surely affect the image at the pixel densities being bandied about these days. It would also be in addition to any aberrations or corrections in the image rays caused by the optical formula itself. I don't know if this is "astigmatism" because I have already exhausted my knowledge optics. s-a Link to post Share on other sites More sharing options...
stevesurf Posted January 17, 2016 Share #148 Posted January 17, 2016 Optimized for digital means that the optical formula has been tweaked to neutralize the astigmatism in the image periphery caused by the cover glass. This also means the lens will not perform as well on film as it will have astigmatism in the periphery. That is basically what Zeiss did with the loxia line for the Sony A7. But Sony doesn't have film cameras so no issues there PS. Another example is the summilux 28, which is tweaked for the thicker cover glass of the SL and performs slightly worse on the M. I would expect its film performance to be proportionately degraded. Sounds logical and seems to be supported here: Two Reasons... ...Why the new Sony A7r might not be a good workhorse for your adapted Leica lenses. Reason 1: Mechanical slop is already a bit of a crapshoot with just one interface. As an adapter adds two more to the system, the chances for slop are multiplied. See Roger Cicala's article "There Is No Free Lunch, Episode 763: Lens Adapters" at LensRentals. And thanks to Nigel for providing the link! Reason 2: Bruno Masset wrote this next as a comment to the A7 post, not as a finished article, but I thought it was interesting enough that it deserved its own slot in the stack. What follows was... Written by Bruno Masset Methinks a lot of people who buy a full-frame mirrorless, hoping to use (for instance) old wide-angle rangefinder Leica lenses using mount adapters, are going to discover how mediocre the imaging performance of such lenses might be on a digital sensor. The Leica M9 sensor's cover glass thickness is 0.8mm; this is much thicker than the M8's 0.5mm, but presumably offers much better infrared filtering, avoiding the "black synthetic fabric being imaged as dark purple" syndrome that plagued the M8. There's little reason to expect that the optical stack (OLPF, IR filter etc.) in front of the Sony A7's sensor is thinner than the Leica M9's. In the film era, lenses were designed to be stigmatic in air. In other words, back in the days when digital sensors didn't exist, lens designers expected the medium present between the lens' last vertex (the rearmost glass surface) and the imaging plane (the film) to have a homogeneous refractive index (RI) of one. Leica's (and other manufacturers') wide-angle rangefinder lenses (those with a focal length shorter than approximately 35mm) tend to have a quite short exit-pupil-to-imaging-plane distance. The exit pupil is the apparent position of the diaphragm, looking at the lens from behind. Obviously, the exit pupil is where the light cone appears to emanate from, and thus determines the tilt of the light cone's principal ray—the cone's "axis," if you will. In the center of the image, the principal ray will be perpendicular to the imaging plane. In the corners of the image, if the distance of the exit pupil to the image plane is short, the light cone (and its principal ray) will be quite tilted. A slab of optical material—a sensor's cover glass, or an optical low-pass filter stack—has a refractive index higher than one, and will spatially shift the light rays impinging upon it—the amount of this spatial shift being dependent on the ray's incidence angle. As a light cone is composed of rays that have varying angles, each of these rays is going to be spatially shifted by a variable amount. The net result is that a light cone that was designed to converge to a single point—i.e., be stigmatic—in air, can have its light rays dispersed all over the place after it passes through a slab of material with refractive index larger than one. The cone's dispersion is negligible when the incidence angle is perpendicular, at the center of the image. With a sensor cover glass thickness of 0.8mm (800 microns) and a RI of 1.5, an exit-pupil-to-imaging-plane distance of about 30mm (a fairly typical value for wide-angle rangefinder lenses with focal lengths less than or equal to 35mm), and a cone aperture of ƒ/4 (that is, an exit pupil diameter of 30mm/4.0 = 7.5mm), one can easily calculate that in the image corners, the light cone's rays, instead of converging to a point, will be dispersed over an area of about 35 microns. On a Leica M9, 35 microns corresponds to about five pixels! So, what was imaged as a point when that film-era lens was used in air, could well become a fuzzy disk of a diameter of about five pixels when the lens is used with a digital sensor! The further from the image's center (where the principal ray is perpendicular, and the cover glass has thus essentially no influence), the worse the image quality will be. Link to post Share on other sites More sharing options...
Rick Posted January 17, 2016 Author Share #149 Posted January 17, 2016 Stevesurf - This has been known from the days of the micro lenses and thin edge cover glass needed for the M9 (FF) sensor. The acute angle of light from the classic Leica RF lenses had to be overcome with design of the micro mirrors and the thin edge cover design. This required color correction for the periphery and it induced UV color problems across the image. We have been plagued to some degree with color issues because of this even on the M240. If, Leica did not have to deal with these ray angle problems from their legacy lenses, they would be able to use a thicker cover glass which in turn would provide better UV correction. The SL was designed from the start without out this handicap for the engineers. Which is probably why, as Edward has pointed out, the new 28 Summilux performs better in the edges on the SL than the M. It was designed for a thicker lens cover. The interesting part isn't so much the known reasons for the thin cover glass and the oblique ray angles from your quoted article, but rather, what is Leica doing here with their redesign of these legacy film lenses. And, what does this mean going forward for our legacy film lenses? Until, we get a chance to see how these new lenses perform on the M (thin cover glass) vs the SL (thicker cover glass), we won't know for sure if Leica is abandoning the thin cover glass design and hence to some degree the legacy film lenses. Rick Link to post Share on other sites More sharing options...
gpwhite Posted January 17, 2016 Share #150 Posted January 17, 2016 Stevesurf - This has been known from the days of the micro lenses and thin edge cover glass needed for the M9 (FF) sensor. The acute angle of light from the classic Leica RF lenses had to be overcome with design of the micro mirrors and the thin edge cover design. This required color correction for the periphery and it induced UV color problems across the image. We have been plagued to some degree with color issues because of this even on the M240. If, Leica did not have to deal with these ray angle problems from their legacy lenses, they would be able to use a thicker cover glass which in turn would provide better UV correction. The SL was designed from the start without out this handicap for the engineers. Which is probably why, as Edward has pointed out, the new 28 Summilux performs better in the edges on the SL than the M. It was designed for a thicker lens cover. The interesting part isn't so much the known reasons for the thin cover glass and the oblique ray angles from your quoted article, but rather, what is Leica doing here with their redesign of these legacy film lenses. And, what does this mean going forward for our legacy film lenses? Until, we get a chance to see how these new lenses perform on the M (thin cover glass) vs the SL (thicker cover glass), we won't know for sure if Leica is abandoning the thin cover glass design and hence to some degree the legacy film lenses. Rick Rick, what are the image quality factors that are being traded off in the M lens designs that are developed for thicker sensor cover glass? I have read on this thread that lenses characterized above as more "tele-centric" than M legacy glass may be larger and heavier. , but my curiosity is really about IQ... are there necessarily, or likely, IQ costs associated with the TCGL (thick cover glass lenses) design? The case of das neues Summicron 28 is intriguing because the estimated MTF suggests the rendering across the frame @ f/2.8 will be improved. This was already a strength of the original Summicron 28, IMHO, so an "improvement" would make for a truly remarkable lens. Where is this going? The newly released lens seems no larger or heavier than the original, and yet performance suggested by MTF figures suggests the TCGL redesign is a step up on both M and SL. So the TCGL design discussion is murky to me. Link to post Share on other sites More sharing options...
Rick Posted January 17, 2016 Author Share #151 Posted January 17, 2016 Hi George, I think you are coming at it a little backwards. The trade offs have been in sensor design to accommodate retrofocus legacy M lenses. These lenses are fantastic, but are hard to design sensors for. Sensors need enough cover glass to filter UV but the thickness and lack of offset micro lenses cause smearing in the edges of the image with retrofocus lens designs. I suspect Leica at some point will cease to utilize esoteric sensor designs and will have to shift M digital lens designs to work with thicker sensors and smaller more densely spaced pixels. I have the feeling these lenses, if they are truly redesigns, represent a direction Leica feels it needs to move in to produce better images with newer sensors. I guess we are seeing just a continuation of what actually started with the WATE, 50 APO, fixing the 35Lux's focus shift, the new 28 Summilux and now possibly redesigns (patches) of these older wides. We'll have to see if these lenses are actually resigned in this way... I still have my doubts how much has been changes. Let's see what happens. Rick Link to post Share on other sites More sharing options...
graphlex Posted January 17, 2016 Share #152 Posted January 17, 2016 If and when such a transition were to be effected, it would certainly be a delicate matter for Leica to explain to its customer base! Link to post Share on other sites More sharing options...
semi-ambivalent Posted January 18, 2016 Share #153 Posted January 18, 2016 If and when such a transition were to be effected, it would certainly be a delicate matter for Leica to explain to its customer base! Higher pixel counts would allow software correction to be applied to smaller sections of the image, allowing better looking image edges right out-of-camera. I imagine this would stave off some worry by those who own perhaps large numbers of vintage Leica lenses. Personally, if the 'digital' lenses actually showed visibly lesser performance on a film camera I'd be quite pleased to know which lenses these are so I could avoid them until such a time that I owned a digital Leica. I would fault them not one bit for doing what they feel they had to do to stay alive in the game. Worst case, my film might not even show the problems with new lenses, and if it did I still get to use those tiny old ones, which is a very big reason I bought into Leica to begin with. s-a Link to post Share on other sites More sharing options...
CheshireCat Posted January 18, 2016 Share #154 Posted January 18, 2016 The trade offs have been in sensor design to accommodate retrofocus legacy M lenses. You mean non-retrofocus. Link to post Share on other sites More sharing options...
pico Posted January 18, 2016 Share #155 Posted January 18, 2016 I guess alternatively they could turn 6 bits into 12 bits or more by adding a couple shade of grey. I'm not smart enough to know what turning a bit to grey would do, but 64 lenses is not enough? Link to post Share on other sites More sharing options...
edwardkaraa Posted January 18, 2016 Share #156 Posted January 18, 2016 Just to clarify my point, I think that no matter what lens design, the glass cover induces additional astigmatism and field curvature. If a new lens is designed from scratch, the designer can easily take the cover glass into account in the optical formula. But as Zeiss did with the ZM based 35 and 50 loxia, Leica can easily tweak existing film designs, with almost no perceptible differences in the lens diagram, in order to create some negative astigmatism and field curvature that counteract the effects of the cover glass. I guess that this is what Leica did with the 28 at least. Since the cover glass of the SL is still considered very thin compared to other cameras, it is not too difficult and actually a much easier task than what Zeiss had to do with the loxia as the cover glass of the Sony is supposedly 2mm thick. Link to post Share on other sites More sharing options...
jaapv Posted January 18, 2016 Share #157 Posted January 18, 2016 All this explains why designs should take digital sensors into account, nothing new, but there is still no explanation that such a design would perform worse on film. Link to post Share on other sites More sharing options...
Guest Posted January 18, 2016 Share #158 Posted January 18, 2016 I wish they would make some more screw mount lenses in the general lens lineup and not as some special editions. As to the new lenses I always thought that the 35mm Summicron ASPH was about as good as it gets and I have never found any fault with it but hey I've seen some brilliant pictures taken with an old 35mm Summaron F3.5!! You of all people on this forum should be aware that it is nothing " or very little " to do with taking picture. Leica will sell thousands of them ,the dealers will have lots of stock of the old model taken in px ,and so the cycle continues. (Grin ) brianp Link to post Share on other sites More sharing options...
edwardkaraa Posted January 18, 2016 Share #159 Posted January 18, 2016 All this explains why designs should take digital sensors into account, nothing new, but there is still no explanation that such a design would perform worse on film. Let me ask you a question: if lenses designed for film don't work well with a cover glass, why should lenses designed for a cover glass work well on film? Don't believe everything Karbe says. He works for Leica after all and Leica wants you to believe that their new M lenses work equally as well on film and digital bodies, and you're free to believe whom ever you want Link to post Share on other sites More sharing options...
jaapv Posted January 18, 2016 Share #160 Posted January 18, 2016 Because the difference will be the reduction of the incidence angle and that is not a factor that is of influence on film. It is not as if there will be deliberate aberrations introduced. Compare (albeit on another level) to optimizing the focusing of lenses for digital The need that emerged for more accurate focus because of digital sensors resulted in lenses that are more precise on film as well. Link to post Share on other sites More sharing options...
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