Purely Optical Solution

[Jack Davidson]

There's a long, very technical, and somewhat heated discussion about this today at cinematography.net. I'm still trying to understand it. Several lens designers as well as some DPs weigh in. It's also enlightening in the "Panavision's corporate culture doesn't get it, Angenieux's does" sort of way. (Or maybe they are right and smarter than everyone else.)

Here's the link http://www.cinematography.net/Pages%...%20cameras.htm

Good luck!

[Jack Davidson]

One thing Galt said that definitely did resonate with me was, "Unfortunately, in practice, a relay lens only works well when designed for a particular prime lens."

That may have something to do with the exit pupil size and why some Cine lenses in fact do not work well with the Ang-Zeiss CLA 35. It must also be why the Zacuto adapter has a different relay to go with each lens.

Good luck to anyone who tries to home-build one. I can barely get my oscillator to consistently work!

[Ryan Damm]

Matt et al -

So I read the discussion on CML. Very interesting, and quite technical. I think I side with Angenieux ('optical relay adapters do exist') for several technical and non-technical reasons.

In this post: nontechnical reasons.

Here's my take on the situation - John Galt is correct, but he's talking about the wrong things.

Some background: I had the pleasure of hearing Mr. Galt speak at CineQuest 2005; he was there representing Panavision at the large-chip section of the "Day of the Cinematographer." He was talking about the Panavision Genesis camera; there were reps from Dalsa (representing their S35-sized single-chip camera) and NHK Japan (showing off a UHD, 32 Mpixel tv system - 8k, 120fps madness). But that's neither here nor there.

Mr. Galt and the Dalsa rep (whose name escapes me) had a remarkable disconnect with the audience. We're talking San Jose, CA - not Hollywood by any means. Most of the questions after the talk were from the low-budget regime, and I imagine most of the filmmakers there were too. What I took away from the talk: if you're low-budget, don't bother with Panavision or Dalsa. Ever. Mr. Galt also refused to engage questions about 35mm adapters, and dismissed the P+S Technik entirely (briefly citing the same technical assertions as in the CML thread, when he bothered to offer an explanation at all). I actually asked about 'optically enlarging the target plane,' basically what the Angeneiux and JVC adapter do, and he more or less dismissed the question.

Mr. Galt can't be blamed too much - for one, it was clear that the audience wasn't all that technical (myself included, at the time). Also, Panavision as a company really isn't interested in the lower-ticket items. (A colossal mistake right now, if you ask me - as distribution channels open up, it's not the large-ticket companies that will own the market, but the huge, huge base at the bottom.)

The real issue, I believe, is one of corporate focus. Mr. Galt's message was handed down from Panavision up on high. They focus on super-high-quality optics. They measure this quality by MTF, by lp/mm, by very technical means. And it's true, by those measures Panavision lenses are very good. But that's really not the whole story. By the technial specifications he cited in the CML thread, you're probably best off using whatever lens shipped with your camera.

As anyone on this thread knows, there's a lot more to the story than that. (And I'll get into that in the next post.)

[Ryan Damm]

Okay, technical reasons -

Let me distill the argument, if I can. John Galt (Panavision) said the MTF would be superior with a lens designed specifically for a 3-chip camera, rather than a 35mm lens + adapter. Basically, he's using resolution as the foundation of his argument.

The other reps - I think Cooke, Angeneiux, etc - never said he was wrong about that point. They just claimed the 35mm + adapter would be good, whereas he seems to think they would be unbearably bad. His arguments about why they would be unbearably bad don't hold much water.

The technical reason was the 'multiplying MTF' argument, mostly. Basically, one of the main causes of reduced resolution in an optical system is aberrations. When you have an intermediate scattering plate, you keep aberrations from building up on either side of the plate, but you do multiply their effect on resolution at each phase (like John Galt was saying, MTF of taking lens x MTF of scattering medium x MTF of relay lens). With an optical setup, you can actually build some correction into the adapter itself - if the MTF of the taking lens is degraded somewhat by, say, undercorrected spherical aberration, you can build some overcorrected spherical aberration into the relay lens. (The situation is vastly more complex, but the general principle is the same.) Mr. Galt also made some points about sensor size which are correct but a bit nit-picky.

So you may see some better performance with certain 35mm lenses - if the corrections that are built in are lens specific, then you may see increased aberrations (decreased MTF, lower contrast and lower resolution) with other taking lenses.

But we're actually splitting hairs here. If you're going to rent or buy lenses, you should do tests first. If real-world tests work for you, get the lens and forget MTF calculations; debates between lens techs are interesting but really far from relevant. When you go to a movie theater, the biggest impact on MTF etc isn't even the lens. It's the fact that the print you're watching is an nth-generation analog reproduction. You're seeing 2-3 or more layers of film grain superimposed on each other. You're seeing misregistered film, you're seeing aberrations in the printing optics, you're seeing flutter in the projector. You're seeing the resolution and color reproduction of print stocks.

In fact, I wonder to what extent this focus on lens quality is a holdover from the analog days, when you had to wring every last drop of resolution out of every step of the way, because the final product would be watered down by a dozen steps of analog reproduction? The fact is, even consumer-grade lenses on consumer HD cameras produce pretty sharp results. Not that it couldn't be better, but to the average viewer, it matters not at all.

But the real reason adapters are of interest to me is the possibility of getting something more than resolution out of lens choice. Things like bokeh, diffraction patters. Working advantages to certain lenses (like focus pulling or even cost).

And in that regard, Panavision's solution isn't for everyone anyway. I'm not interested in renting lenses from them, not if I own a bunch of still lenses that I want to use (or even if I want to build some myself). And I'm not interested in what they're interested in - resolution at any cost. I think there's some interesting things about old lenses that I miss in new ones.

For example: ever look at the focus blur in modern movies (or CSI, for example)? Ultra sharp, dinner-plate blurs. Sharp edged and crisp and totally artificial. Neon-green lens flares in mile-long cascades.

Then look at street lights out-of-focus in your own eye, through scratched glasses or in the rain. Totally different. Interesting in its own right. The blur pattern in most people's eyes couldn't be more different than the perfect-disc blurs of Panavision.

And with a world of lenses already out there, why would I want to restrict myself to the five or six, or even ten that Panavision chooses to release? I could really care less about the ultimate MTF. I want the freedom to choose lenses that fit my needs, even if my needs are a little retro, or funky, or just different. Motivated partly by cost, but even more by aesthetic concerns.

I mean, how boring would it be if every digital production used the same lenses just because they had the highest lab resolution?

So I have to disagree with John Galt's main point (not any of his specific arguments): relay lenses aren't pointless. And as the CML thread more or less concludes, we'll see at NAB.

[Ryan Damm]

Before we get too excited about these adapters:

The Angenieux adapter is an f/1.4 system. It does get the DOF characteristics of a 35mm lens, but not at f/1.4. The maximum working aperture of the taking lens is restricted to f/3.5 (the image side - the 2/3" chip - is working at f/1.4). If you open the taking lens up beyond f/3.5, you're just adding light to the lens system that won't get picked up in the final image (and won't contribute size to the individual defocus blurs).

And with regards to the JVC adapter, the same holds true. There's a limiting aperture in the adapter that will affect the largest aperture you can work at. This will be true of all optical adapters (no scattering plate) due to the optical invariant. In fact, you get basically the same depth of field that you'd get with a really large-aperture lens designed for a 2/3" (or 1/3" chip).

So with the JVC adapter, you're probably limited to the DOF of a 16mm lens at a medium aperture. Not crazy-narrow. But at least you get the optical characteristics of a wide selection of professional lenses. And you get other (non-DOF) advantages, like diffraction patterns, flare properties, and the ability to play nice with focus pullers, matte boxes and other toys.

If you really wanted the full aperture of the taking lens, the relay lens would have to satisfy the condition:

1/magnification=(f/# taking lens)/(f/# relay lens);

In other words, if you shrink the image by, say, 2.5 (35mm to 2/3" chip), your working f/number must increase by the same amount (f/2.0 becomes the impossibly small f/0.8). Note that if you merely had a taking lens with the same f/number as the relay optics, you'd have the same small DOF as if you were shooting on a larger format at a more reasonable f/number.

But... you'd only have to correct the relay optics for one specific conjugate, so it's not as impossible as it seems.



Okay... time for lunch.




*I think these are the figures, but feel free to double check or second-guess*

2/3" = 11mm diagonal
1/3" = 6.5 mm diagonal
35mm cinema = approx 28mm diagonal
16mm cinema = approx 13mm image diagonal

[Jack Davidson]

Thanks Ryan,
you just made me feel even dumber-er.

[Ryan Damm]

I dunno, Jack - which is dumber-er: reading posts on DVinfo to get to the bottom line, or spending countless hours reading optics textbooks in your spare time? (I have yet to get paid for a smidgen of optics knowledge, and it doesn't exactly make for good cocktail party conversation.)

[Tim Dashwood]

I just posted some footage from my HZ-CA13U test at Sundance.

http://www.dvinfo.net/conf/showthread.php?t=85007

[Ben Winter]

Thanks Tim.

It could just be me, but the DOF doesn't seem that strong in that footage. Like the out of focus areas aren't defocused nearly as much. That's probably the 16mm speaking and I'm just used to 35mm...

[Tim Dashwood]

Originally Posted by Ben Winter

Thanks Tim.

It could just be me, but the DOF doesn't seem that strong in that footage. Like the out of focus areas aren't defocused nearly as much. That's probably the 16mm speaking and I'm just used to 35mm...

I've been told that the equivalent frame size is somewhere around 16mm/Super-16, so the short DOF won't be as pronounced as you may find in 35mm.

However, the 16mm focal length lens did feel a bit wider than I would have expected if the same lens were mounted to a 16mm or even a super-16 camera.
As you can see from the still photos, I was very close to the subjects and still getting "head and shoulder" framing.
There is no official literature on this device yet, so I'm just going by the bits and pieces I can get out of the JVC guys at these events.

The big surprise for me was the almost complete lack of chromatic aberration. If figured there would be some sort of distortion with whatever optical elements they have in there, but the footage seemed sharp edge to edge with no color separation.

[Ben Winter]

Originally Posted by Tim Dashwood

I've been told that the equivalent frame size was somewhere around 16mm/Super-16, so the short DOF won't be as pronounced as you may find in 35mm.

However, the 16mm focal length lens did feel a bit wider than I would have expected if the same lens were mounted to a 16mm or even a super-16 camera.
As you can see from the still photos, I was very close to the subjects (within 2 feet) and still getting "head and shoulder" framing.
There is no official literature on this device yet, so I'm just going by the bits and pieces I can get out of the JVC guys at these events.

The big surprise for me was the almost complete lack of chromatic aberration. If figured there would be some sort of distortion with whatever optical elements they have in there, but the footage seemed sharp edge to edge with no color separation.

Actually I noticed vertical red/green chroma aberration on a lot of the out-of-focus highlights. Take the first shot for example. The white bar on top of the car has a green edge on top, red on bottom. Looks like it pops up a lot in a couple other places too.

I must say the in-focus areas are extremely sharp though.

[Jack Davidson]

Ben's got better eyes than I do. Nice job, Tim & JVC!!

[Ben Winter]

Haha. I guess every imaging system has its flaws. Overall it's great image, don't get me wrong :)

[Tim Dashwood]

Originally Posted by Ben Winter

Actually I noticed vertical red/green chroma aberration on a lot of the out-of-focus highlights. Take the first shot for example. The white bar on top of the car has a green edge on top, red on bottom. Looks like it pops up a lot in a couple other places too.

I must say the in-focus areas are extremely sharp though.

Yes, as with any optical system there is always going to be some amount of CA. However, compared to what we have become accustomed to with 1/3" 3-CCD imagers paired with low-cost zoom lenses, this new system is amazing.

The new HD200 and HD250 also have lens shading capabilities, so this may also be a factor. I have no idea if the prime was programmed into the lens shading memory before I tested it.

[Carlos Serrano]

http://www.distantfocus.com/projects/montage/