Sony PL 35mm 50mm 85mm Glass DOF Compared on PMW-F3 Camera

[timbook2]

^ Yup! Hunter got it.

Since all digital cameras don't have spinning shutters (unless we ever see an optical-reflex Alexa) the lens designers can take advantage of the 52mm flange depth in the PL mount. For reasons Steve Castle explained to me in an earlier post in this thread, this extra room can be taken advantage of. The people at Angeniuex did take advantage of this, and by doing so, were able to make a quality set of optimo zooms for almost half the price (and size!) of their big brothers.

If you can find photos of the lenses, you'll see the angeniuex DP's have a lot longer rear element.

Thanks for the explanations.

 

[Steve Castle]

I would like to argue that the lenses above the photosites still have a flat plane which needs to be focused upon... In other words if you are planing to balance say a peice of hard flat glass on top of a basket ball, sure the ball is round, but the glass sits at the top most plane. Same as would be the lighting aiming for the sensors top layer. Those lenses are focusing the light into the photosite for just that reason, to make sure light is passing directly through and not being curved. The photons travailing are hitting the very top of those lenses first. Thats the same image plane you'd then have just like film. And again film is layers. Probably closer to measurements equal to that of those lenses over the photosites. Remember we are talking in the microscopic world.

I would have to say that even if there is a difference between the two, we are talking so minimal... Plus I've never heard of a lens being made for a cmos sensor vs. a film plane. They make different lenses designed for cmos vs. 3chip but Ive never heard of a PL lens being made with a Cmos sensor in mind over a film plane.

Think about how light entering the lens would microlens in the center of the sensor compare that with how light will hit at the very edges of the sensor. At the very edges light is approaching these mircolenses are at a very oblique angle.

For this reason there is a very big difference between film and sensor lenses in terms of design. If you think about it two-dimensionally than the focal plane of lens is uniform throughout the entire surface of the sensor, but it isn't. There needs to be consideration that througout surface area of the sensor filled with microlenses that light will be hitting it differently.

So modern digital lenses try to keep angle of the projecting rectilinear image as even as possible at the fringes of the sensor, this is built into the design of the lens elements themselves. Also to reduce internal reflection an additional low-dispersion element is added to reduce ghosting. Look at the modifications that Zeiss to the Contax lenses that share the same overall design as the ZF/CP2.

For cameras that are primarily using film-lenses and have a short FFD, like the Leica M-bodies, we have the fringes of the sensor has off-set microlenses so that on the sensor side it can correct lateral CA that film lenses will ultimately have. Offset microlesnses won't work with the F3 however because the camera will be using lenses with different FFD (PLs & F3 mounts),

 

[Steve Castle]

I think pictures are easier to understand (restated my previous post in pictures).

So as we know, a lens projects an image circle onto a light sensitive medium. At the center of the lens light is hitting the medium at a perfectly perpendicular straight, as we get to further away from that central radius light is hitting the surface at an angle.

This is how light hits the flat surface of film compared with microlenses on a sensor:

What happens as we get further away from the center of the lens is that the angle hitting the surface gets steeper. This becomes a bigger issue for microlenses as the surface structure is three-dimensional and the light is hitting the side of the lens. Since the pixel is positioned within a well below the microlens, the depth of the well will lead not only offset projection but also shadow off of the well walls (this is a bigger issue as the pixel gets smaller).

This becomes a bigger issue for lenses that are projecting larger image circles and have a shorter FFD (such as the Leica Ms) as the angle becomes steeper as light radiates towards the edge of a larger area. So this is not much of an issue for 16mm and 2/3" lenses, compared to a S35, compared to a FF35.

But all lenses are designed to have a "sweet-spot", where optical image performance is designed to achieved relative to a certain image circle. Digital lenses are designed from the beginning with the digital sensor in mind relative to their target crop. Keep in mind that film also have lateral CA issues as well at the edges, but they are nowhere near as pronounced as a sensor. Furthermore, the design of the lens needs to be adjusted with the microlens in mind. Modern digital lenses have adapted to meet these needs.

Another issue is that since the surface area has optical peaks and valleys, these lenses will reflect light off each other produce ghosting. For instance, some modern lenses, such as the Nikkor 200-400mm, no longer have a flat front lens element, they are curved meniscus and specially-coated to inhibit internal re-reflection of sensor elements.

In regards to video. The resolving needs of video are very low for 1080p/2k camera, so a lot of these optical imperfections have gone by unnoticed. These optical differences are more strikingly apparent in still-photography as resolving needs of modern sensors have started to expose these optical deficiencies.

Moreover we are moving to 4K+ sensors and PL lenses are getting cheaper and more mass-produced compared to traditionally expensive, and optically extravagant PL lenses. Which is why having these Sony primes specifically designed for digital-sensors and a S35 sweet-spot is so crucial.

 

[Andrew Stone]

That is remarkable Steve. Thanks for taking the time to spell it out and provide the illustrations. Quite staggering the complexity of what is involved with these digital sensors.

 

[G.P.]

To steve... I understand all of the physics involved and have seen/read/and attended more things about CMOS sensors than I care to mention... But my point is this... I have never heard of a PL lens manufacturer making lenses specifically for CMOS sensors.

Also those lenses above the photosite is made to correct for the distortion, not cause it. They are there to direct as much light directly into the photosite, so there isn't a lot of unused photons missing the center.

Other than maybe implementing an anti-reflective coating on the rear element of the lens or bringing the depth further in due to not having a mirror in the way, there is no information anywhere backing up a statement of mass PL lenses being specific to a sensor. If anything PL manufactures are NOT building lenses for the digital world, they are making for the mass use which is still film.

Besides that CCD sensors are what rule the major motion picture side of things, not CMOS. F35, F23... list goes on, but those cameras are all made with CCD sensors, not CMOS.

 

[Steve Castle]

To steve... I understand all of the physics involved and have seen/read/and attended more things about CMOS sensors than I care to mention... But my point is this... I have never heard of a PL lens manufacturer making lenses specifically for CMOS sensors.

Also those lenses above the photosite is made to correct for the distortion, not cause it. They are there to direct as much light directly into the photosite, so there isn't a lot of unused photons missing the center.

Other than maybe implementing an anti-reflective coating on the rear element of the lens, there is no information anywhere backing up a statement of PL lenses being specific to a sensor. If anything PL manufactures are NOT building lenses for the digital world, they are making for the mass use which is still film.

S35 CMOS sensors cameras with PL mounts have only started appearing with the Red One, and very recently the Alexa. This still is a fairly new market, which doesn't have the speed or flexibility of product development of larger volume markets.

A lot of older PL lenses are in fact designed for film, however I would wager newer PL lenses such as the Red lenses (which is rumored to be using Sigma as a supplier) are using modern slr-based lenses designed for digital sensors. Same goes with these new Sony Primes.

If you want to look at a lens that has evolved from film to digital, look at the Zeiss CP2 lenses. They were originally based on optics found on Contax C/Y mounts licensed by Kyocera and targeted for film. As the agreement ended in 2006, those film lens designs were adapted by Zeiss to ZE/ZF/CP2 lenses for modern CMOS sensors. These modifications weren't just new lens coatings but completely new elements within the lens and more subtle changes (21mm F2.8 Distagon to CP2 21mm T2.9 is a good example). The newly expanded Zeiss CP2/LWZ.2 line-up goes further in this direction (in fact, Zeiss advertises how well these lenses handle internal reflection which is a CMOS specific problem).

Also, microlenses doesn't exist to correct lens distortion; it has nothing to with lens distortion. They are designed to focus the light onto the active detector regions and are generally agnostic to what lens is on the camera (with the exception of the aforementioned Leica using Kodak's offset microlens sensor). They are a fundamental characteristic of a modern sensor that must be considered when designing a lens.

The reason why I originally brought this topic up is because the PL mount are one of the few bastions where lenses are still transitioning from film to digital. All the stuff I mentioned hitherto is a given, and just plain basic common sense on the still photography side. And as more S35 CMOS cameras are released we'll see the PL market evolve along with it.

 

[Ryan Patrick O'Hara]

Hmmmm... Edited, until I figure out what 'digital' optimized really is.

 

[ken37]

Thanks for this, and for your other posts. Very informative. If I could put you on the spot for a moment, Steve, -- since some of the recently released PL Primes are designed for digital sensors as you've pointed out, do you have a line from a certain manufacturer that you would recommend? Personally, I'm interested in purchasing a w/a cine zoom, with an assortment of mid to telephoto primes. I'm willing to pay for quality, but I don't need the highest-level stuff. If you don't feel comfortable naming names, I totally understand.

 

[Mitch Gross]

This has little to do with CMOS v. CCD. It is all about designing lenses to be telecentric, meaning that the light project from them to the sensor in as acute an angle as possible. Pnavision lenses are naturally telecentric since the mount throat is so deep. Most Optimos are as well. There have been machine vision lenses designed this way for years.

PL Lenses promoted as being designed specifically with electronic sensors in mind include:
Fuji Premier PL zooms
RED Pro Primes
Schneider Cine-Xenars
UniQoptics Signature Series

 

[Steve Castle]

Hmmmm... Edited, until I figure out what 'digital' optimized really is.

"Digitally Optimized" means that lenses are designed to have light hit the sensor parallel to the optical axis as possible. As I've explained above, mircolenses handle light hitting it at an angle very poorly. Explained another way, sensors lose half their sensitivity when the light diverges just 15-20 degrees from the optical axis.

So optically there are a LOT of design changes that have been made to modern digital lenses.

As Mitch Gross has already explained, it means that all modern lenses designed for sensors are telecentric or 'near telecentric'. What this has meant for lens design is that exit pupil has to be taken further out away from the sensor plane. Compared to film days, modern lenses have their exit pupil near the optical center of the lens.

For dSLR lenses most are what's called 'near telecentric". To be fully telecentric the exit pupil needs to be at infinity, and light diverges zero degrees from the optical axis. This is cost prohibitive in many cases, especially when you are trying to sell a $200 lens. So the exit pupil isn't at infinity but near it as cost will allow, so if the 'virtual' exit pupil is around 80mm from sensor surface then light is hitting the corners at around ~9% angle of incidence for a Super 35mm surface area.

For high-end cinema lenses you have these very large rear lens elements for the sake of telecentricity (think about your Optimo DP post and short FFD conversation earlier in this thread), a great thing about a telecentric lens is that it compensates for lens breathing. So there is still this gap in telecentric performance that is very relevant to video, as it impacts focus breathing, and this gap is what separates a 'good' from an 'excellent' cinema lens.

Thanks for this, and for your other posts. Very informative. If I could put you on the spot for a moment, Steve, -- since some of the recently released PL Primes are designed for digital sensors as you've pointed out, do you have a line from a certain manufacturer that you would recommend? Personally, I'm interested in purchasing a w/a cine zoom, with an assortment of mid to telephoto primes. I'm willing to pay for quality, but I don't need the highest-level stuff. If you don't feel comfortable naming names, I totally understand.

Ryan has an excellent post earlier in this thread that breaks down different lenses. Its a great resource:

http://www.dvxuser.com/V6/showthrea...MW-F3-Camera&p=2196002&viewfull=1#post2196002

 

[Ryan Patrick O'Hara]

1) What are the negative optical effects of a very "non-close to telecentric' lens?


2) How does one measure the telecentricity of lenses?



I'm asking because I'd like to know what to look for and how to measure lenses that don't advertise as being 'made for digital' but that I suspect perform just as well.

 

[Mitch Gross]

Darkening of the image as you get closer to the edges.

 

[G.P.]

See my thing is this, everything I've used lens wise, has been lenses made for the Film world. Arri's and Cooke lenses and even some old Nikons. I've never seen any of those lenses perform bad on a digital cinema camera...

I've never seen a set of Arri's look bad on a RED one in comparison to RED Pro primes... in fact I've seen the Arri's look and feel better... I don't understand how someone could say that just because the lens is supposedly made for a digital sensor actually out perform the best Film lenses ever made.

I still think a set of s/4 Cooke's could look better than some new RED Pro primes even though according to what you're saying RED Pro primes are specifically made for that sensor. It's one thing to say "yes this lens is made for digital" and its another to say "this lens looks great on digital".

I would never rent a set of RED Pro primes or CP.2 primes if they were the same exact set and price as say a set of Arri Masters or Cooke's. The others just look/feel better. I believe the organic feel of the lens is way more important to some very minimal effects cause by the sensor... I've seen Arri Alexa footage shown on the big screen, as well as the F3, and of corse most people have seen the F35 on the big screen by now either digitally projected or print. All of those I've seen, I never sat there looking at the beautiful footage from classic lenses that were used on digital cameras and said... "hmm that doesn't look as good as my RED Pro primes on the RED one." I still think classic lenses look better and feel better, and create a more organic look than some of these newer lenses that have a more sterile feel to them.

I know the tech talk behind it all, and I know there is a difference. But in the argument brought up originally I don't think its the right place to say that the Sony Primes should be made for the digital use... I mean heck thats kind of a give in that they are. They are specifically made FOR the F3, you can't even buy them if you wanted to for anything else. But that shouldn't be an end all to if you like the lens or not. It should be how it looks, not what sensor it was made for. I care about how it looks, I'm a cinematographer, thats my job. If it looks good, and works right, then I dont care what its made of.

 

[Steve Castle]

1) What are the negative optical effects of a very "non-close to telecentric' lens?


2) How does one measure the telecentricity of lenses?



I'm asking because I'd like to know what to look for and how to measure lenses that don't advertise as being 'made for digital' but that I suspect perform just as well.

There are some applications, such as geospatial analysis, which true telecentricity is an absolute necessity. When you're looking at a satellite photo of Kim Jong Il's missiles and trying to determine the size based on the shadow it projects on the ground, you better be using a true telecentric lens to insure that there aren't any optical distortions. Less extreme is theodolites, telescopes, and microscopes. And for these lenses that really do require telecentric lenses they'll tell you by what degree they are telecentric.

But in cinema terms, that level of accuracy isn't important as long as it 'looks' good. For cinema, telecentric lenses means less focus breathing, better close focus performance, and evenness of illumination of the frame.

At the same time, being telecentric doesn't necessarily mean a camera has better image quality. The image quality is impacted by so many other design elements of the lens. The MTF charts should be one of the main things to study not marketing speak or slogans.

But practically speaking, the simplest way to generalize how telecentric a lens is by looking at it. Compare a CP.2 to a Master Prime. Look at the relative diameter of the rear element, its a good indicator.

 

[Steve Castle]

See my thing is this, everything I've used lens wise, has been lenses made for the Film world. Arri's and Cooke lenses and even some old Nikons. I've never seen any of those lenses perform bad on a digital cinema camera...

I've never seen a set of Arri's look bad on a RED one in comparison to RED Pro primes... in fact I've seen the Arri's look and feel better... I don't understand how someone could say that just because the lens is supposedly made for a digital sensor actually out perform the best Film lenses ever made.

I still think a set of s/4 Cooke's could look better than some new RED Pro primes even though according to what you're saying RED Pro primes are specifically made for that sensor. It's one thing to say "yes this lens is made for digital" and its another to say "this lens looks great on digital".

I would never rent a set of RED Pro primes or CP.2 primes if they were the same exact set and price as say a set of Arri Masters or Cooke's. The others just look/feel better. I believe the organic feel of the lens is way more important to some very minimal effects cause by the sensor... I've seen Arri Alexa footage shown on the big screen, as well as the F3, and of corse most people have seen the F35 on the big screen by now either digitally projected or print. All of those I've seen, I never sat there looking at the beautiful footage from classic lenses that were used on digital cameras and said... "hmm that doesn't look as good as my RED Pro primes on the RED one." I still think classic lenses look better and feel better, and create a more organic look than some of these newer lenses that have a more sterile feel to them.

I know the tech talk behind it all, and I know there is a difference. But in the argument brought up originally I don't think its the right place to say that the Sony Primes should be made for the digital use... I mean heck thats kind of a give in that they are. They are specifically made FOR the F3, you can't even buy them if you wanted to for anything else. But that shouldn't be an end all to if you like the lens or not. It should be how it looks, not what sensor it was made for. I care about how it looks, I'm a cinematographer, thats my job. If it looks good, and works right, then I dont care what its made of.

The reality is that if you aren't looking for specific optical flaws the chances are you aren't going to notice it, this is even more so with video compared to pixel-peeping an ultra high-res still photograph. The image quality of modern lenses is extraordinarily good and its very difficult to differentiate between lenses that are already high caliber. While there are some tells to lenses, in general the optical deficiencies aren't striking or aren't obvious except in set of circumstances.

Also, for high-end cine lenses such as the Master Primes they are near telecentric, which means that they are well suited for digital sensors as the angle of light hitting the sensor is almost parallel. I've explained in the other post that the originally this is designed to reduce breathing since telecentric systems can create an image that maintains constant size at varying object distance, but also has the benefit of being well suited for image sensors.

This should illustrate that having light hit the sensor as parallel as possible is even more crucial with the modern cinema lenses because it has such a large impact in multiple factors.

The issue at hand then is that there are degrees of telecentricity, not all lenses can have the luxury of costing five-figures, and not all lenses are created the same. These Sony primes are a little over $2k each when purchased in a kit, we should expect that the optical elements may be sourced from other higher-volume SLR lenses that may not be designed for this camera. My original post wasn't just about lenses and digital sensors, but rather that these lenses need to be designed to best fit this camera.

 

[Duke M.]

My original post wasn't just about lenses and digital sensors, but rather that these lenses need to be designed to best fit this camera.

Playing the devils advocate, and acknowledging that Sony's engineers know something about combining lenses with cameras, do you have any evidence that they weren't designed or selected for suitability with this camera?

The images I've seen so far have certainly looked great, without ghosting, light loss, etc. that I'd expect for the issues you've mentioned. In all probability they are 'nearly' telecentric since those issues don't appear to have arisen and I don't see a slight vignette type of effect.

 

[Steve Castle]

Playing the devils advocate, and acknowledging that Sony's engineers know something about combining lenses with cameras, do you have any evidence that they weren't designed or selected for suitability with this camera?

The images I've seen so far have certainly looked great, without ghosting, light loss, etc. that I'd expect for the issues you've mentioned. In all probability they are 'nearly' telecentric since those issues don't appear to have arisen and I don't see a slight vignette type of effect.

I'd agree that the early images from the Sony primes look great. And we can only speculate as to if this lens is designed in-house, or outsourced to the many lens suppliers in Japan. While I'm discussing however is what differentiates a good lens from a great lens.

But there are some indications that these lenses may be supplied by slr optical components (keep in mind this is also true for Red's lenses and Zeiss CP.2 as well). Complicated lens elements, such as the aspherical elements, are very expensive to bespoke manufacture in low-volumes. Its much more cost efficient to use these components from other lenses and design around them; you can actually increase telecentricity by adding specific elements near the rear of the lens. The announced zooms seem to be suspiciously close to some dslr lenses (11-16mm f/2.8, 18-270mm F/3.5-6.3) Also we have a lack of proper witness marks, telecentricity improves distance accuracy (though Sony could have probably just gone ahead and labeled the lenses like some other manufacturers).

But the fact is that an APS-C dSLR lens is going to look pretty good on a S35 sensor. The problem has never been an issue of image quality as the resolving needs of a modern dslr surpass any S35 digital camera (though APSC lenses have tended to steer towards the lower-end of the market). The real issue of dSLR lenses for cinema has been an issue of usability. This is addressed with the Sony primes.

Obviously these lenses will focus the right way and the aperture will be click-less, and the early complaints of the pre-production lenses of the focusing mechanism seeming tight indicates to me that Sony has made the tolerance of the focusing mechanism very small to reduce image shift issues. Which is a good thing. Newer reports have it as much smoother, and problem with dSLR lenses is that the focus mechanism is made very loose and light for quick AF so focusing can be very wobbly. So even if certain components may be supplied from other cameras it doesn't mean it can't be a great lens with the right modifications, though they may have had some compromises in design and these lenses could have been even better if they are completely bespoke.

The fact is these lenses are very affordable, and I'm sure once supply allows they'll eventually sell them individually. From just a noticeable image quality perspective there won't huge chasm between these lenses and more expensive mid-range PLs. So the economics of out-right owning a PL lens versus renting comes into play. While this calculation will change individually, I think a lot of folks will start to more closely ask exactly what they are getting out of their lenses.