Zeiss T2.1 Standard Speed with RED

rory hinds · October 13, 2007

anyone had experience with using Zeiss Standard Speed T2.1 lenses with the RED?

I'm looking at purchasing a set with 16mm, 24mm, 32mm, 50mm & 85mm and have read that the 16, 24 & 32 will have a porthole effect as the exit pupil is too small.

Would be great to hear from someone who is using Standards on the RED.

Dan Goulder · October 13, 2007

anyone had experience with using Zeiss Standard Speed T2.1 lenses with the RED?

I'm looking at purchasing a set with 16mm, 24mm, 32mm, 50mm & 85mm and have read that the 16, 24 & 32 will have a porthole effect as the exit pupil is too small.

I wasn't aware of that limitation. However, if it's true, then the RED will be limited to using lens sets that cost (used) even more than the camera body itself. (so much for the "low cost" alternative for the masses)

John Sprung · October 15, 2007

Do they vignette on Super 35? Red is supposed to be the same size.

-- J.S.

Stephen Williams · October 15, 2007

Do they vignette on Super 35? Red is supposed to be the same size.

-- J.S.

Hi John,

The problems I encountered was portholing not vignetting. Wide open there is a slight issue when you stop down it goes away. Similar issues occur with a P+S adapter, the main reason that SuperSpeeds are so expensive today is that they work with a P+S.

Remember a 16x9 S35 is not very different in size to 4x3 academy. Full gate S35 clearly requires a larger circle of coverage.

Stephen

John Sprung · October 16, 2007

The problems I encountered was portholing not vignetting. Wide open there is a slight issue when you stop down it goes away. ... Remember a 16x9 S35 is not very different in size to 4x3 academy. Full gate S35 clearly requires a larger circle of coverage.

Aren't portholing and vignetting the same thing, only with sharper or softer edges on the circle of coverage? I found some actual dimensions for the Red sensor: 0.961" x 0.539". That's a little bigger than 35/4 perf TV trans (0.945" wide), but narrower than the full silent aperture (0.980"). D-20, Genesis, and 35/3 perf are all smaller than 35/4, but not by a lot. The smallest is 3 perf, 0.910" wide.

Figuring diagonals/diameters, Red would be 1.102", the Academy camera aperture is just slightly smaller, 1.073", and 4 perf HDTV Trans is 1.084"

-- J.S.

Mitch Gross · October 16, 2007

It is a different issue. Vignetting is an issue of general lens coverage--how wide is the circle of light tranmitted out the rear of the lens to the image plane. But with digital sensors the problem comes with the angle at which this light is transmitted. Film is essentially a flat surface with it's imaging surface on the top (well, 11 or so layers of it start at the top), but a digital photosite is constructed like a little bucket. If the light is travelling at an acute angle then it may come in at the top of the bucket but some or all of the light may not make it down to the base of the bucket where the sensor material lies. For some older lenses with small exit pupils (small back elements) or some older zooms, this angled light can cause darkening along the outer parts of the frame in a circular shape -- the "portholing" effect described. This is why RED announced "digital ready" lenses, which means that their glass is designed to evenly cover their sensor.

George Lekovic · October 16, 2007

Hi John,

The problems I encountered was portholing not vignetting. Wide open there is a slight issue when you stop down it goes away. Similar issues occur with a P+S adapter, the main reason that SuperSpeeds are so expensive today is that they work with a P+S.

Remember a 16x9 S35 is not very different in size to 4x3 academy. Full gate S35 clearly requires a larger circle of coverage.

Stephen

I shot my last movie entirely on that Zeiss glass. A lot of it was wide open, shot on 3-perf, with what I believe was a S35 gate and I saw no problems in post. You can check the trailer out here, although you can't really tell much from this small of a file:

www.kinokamera.com/polycarp/polycarp.mov

Cheers

Stephen Williams · October 16, 2007

I shot my last movie entirely on that Zeiss glass. A lot of it was wide open, shot on 3-perf, with what I believe was a S35 gate and I saw no problems in post. You can check the trailer out here, although you can't really tell much from this small of a file:

www.kinokamera.com/polycarp/polycarp.mov

Cheers

Hi George,

There is no problem whatsoever using these lenses with a film camera. They were designed to be used on film.

Stephen

John Sprung · October 16, 2007

.... but a digital photosite is constructed like a little bucket. If the light is travelling at an acute angle then it may come in at the top of the bucket but some or all of the light may not make it down to the base of the bucket where the sensor material lies.

Very interesting -- thanks for that. It sounds like more of a pothole than a porthole. ;-)

-- J.S.

George Lekovic · October 18, 2007

Hi George,

There is no problem whatsoever using these lenses with a film camera. They were designed to be used on film.

Stephen

Thanks Steven,

I was unaware that digital sensors (as Mitch pointed out) are actually not an evenly flat surface... I thought that it had something to with the size of the recording surface, not the shape. But thanks - although it does not help much, since I did want to use my (eventual) RED with these lenses...

Cheers/george

Keith Walters · October 18, 2007

Thanks Steven,

I was unaware that digital sensors (as Mitch pointed out) are actually not an evenly flat surface... I thought that it had something to with the size of the recording surface, not the shape. But thanks - although it does not help much, since I did want to use my (eventual) RED with these lenses...

Cheers/george

Strictly speaking, none of the current sensors being used are "Digital". In both CMOS and CCD designs, the light gathering photocells are strictly analog devices.

The same silicon surface has to be used both for gathering photons and turning them into electrical charges, and transferring the resulting pattern of electric charges off the chip and into the processing electronics. The more silicon "real estate" that is used for making the readout electronics, the less there is available of light gathering, so the sensitivity of the chip suffers.

With CCD sensors, the photocells themselves can also double as the readout electronics, so more of the silicon surface can be devoted to light gathering. The design of frame transfer CCD used in the Dalsa origin actually dates back to the early 1970s. Because it has a mechanical shutter to prevent vertical smear during the readout time, a very simple design can be used for the chip where the entire readout operation is handled just by the photocells, with no need for any other on-chip electronics. Nearly all the silicon surface can be devoted to light gathering, which is one reason the Origin has such good low-light sensitivity.

Most CCDs these days are a compromise design where the photocells do some of the work of readout, with extra parts that allow relatively vertical-smear free readout without needing a mechanical shutter. With most of them, only about half the silicon surface ends up getting used for light gathering, which produces a one-stop loss of sensitivity. This has been overcome to a certain extent by so-called "Microlens" technology. During the chip manufacturing process tiny dabs of plastic powder are printed onto the photocells, and when this is heated it melts to form tiny clear droplets, (which look like microscopic dew drops). These act as tiny lenses, concentrating the incident light that falls on each photocell area onto the photosensitive area.

CMOS sensors need a complex network of connecting wires and switching transistors to do the same job as a CCD, which means that there is far less silicon available for actual light gathering. Whereas CCDs can still work OK without microlenses, CMOS sensors really can't work without them. Because the light has to be focussed onto a smaller area, the fabricating of the microlenses is much more difficult.

And, as has been mentioned, the efficiency of the microlenses varies somewhat with the angle the incident light falls on them, causing the "porthole" effect, although I don't think anybody has complained about this on any of the RED footage shown so far.

This effect can be minimized with careful lens design, but if you need a special lens, that does somewhat erode the benefit of having a 35mm-sized sensor in the first place.

John Sprung · October 18, 2007

And, as has been mentioned, the efficiency of the microlenses varies somewhat with the angle the incident light falls on them, causing the "porthole" effect, ...

Hmmm -- so they're actually more like speed bumps than potholes. ;-)

-- J.S.

Lance Flores · October 19, 2007

Hmmm -- so they're actually more like speed bumps than potholes. ;-)

-- J.S.

Oh so droll John

Keith Walters · October 21, 2007

Hmmm -- so they're actually more like speed bumps than potholes. ;-)

-- J.S.

I don't think it's that big a problem. To my knowledge, nobody has complained about it with the D-20, and that just uses ordinary film lenses. It might be one of those things that you'll see if you're actually looking for it, but nobody else will notice. Certainly, you'd have good reason to complain if a top-dollar camera like the Genesis did something like that; but what do you want for $17,500?

Hal Smith · October 21, 2007

The technical term for a lens that has light rays hitting its target "straight on" is Telecentric.

From Wikipedia:

Image space telecentric lenses

An image-space telecentric lens produces images of the same size regardless of the distance between the lens and the film or image sensor. This allows the lens to be focused to different distances without changing the size of the image.

At the film or image sensor, all of the chief rays hit "straight on", or at zero angle of incidence. This property minimizes any angle-of-incidence dependence of the sensor, or of any beam-splitter prism assembly, such as a color separation prism in a three-CCD camera, behind the lens.

Image space telecentric lenses have an exit pupil infinitely far in front of the lens; this is, if you look in the back, the apparent aperture is very far away.

The Olympus Four Thirds System specifies a very distant exit pupil (nearly image side telecentric lenses), to avoid the vignetting and color crosstalk that occur in Bayer pattern image sensors with oblique incident rays. Many lenses that have been specially optimized for digital SLR cameras are nearly telecentric on the image side, and consequently have very small angles of chief ray angles of incidence.

http://en.wikipedia.org/wiki/Telecentric

Keith Walters · October 23, 2007

Somebody has already shot a commercial with a RED, just using ordinary Zeiss Cine lenses. I can't see anything wrong with the pictures they have available for download, and the alleged portholing doesn't seem to happen with other super-35 CMOS cameras, so I don't think this is a real issue.

What is interesting is the number of people who seem surprised to discover that, apart from the extra resolution, it behaves pretty much like a video camera.

Edited October 23, 2007 by Keith Walters

Mitch Gross · October 23, 2007

Only certain focal lengths have that problem and it varies acording to T-stop. That plus the black background could mean that they had no issues.

Stephen Williams · October 23, 2007

Somebody has already shot a commercial with a RED, just using ordinary Zeiss Cine lenses. I can't see anything wrong with the pictures they have available for download, and the alleged portholing doesn't seem to happen with other super-35 CMOS cameras, so I don't think this is a real issue.

What is interesting is the number of people who seem surprised to discover that, apart from the extra resolution, it behaves pretty much like a video camera.

Hi Keith,

3 months ago I tested some Zeiss Standards on a Phantom HD, the wider ones did indeed porthole when wide open. By T4 they were fine.

Stephen

Keith Walters · October 24, 2007

Hi Keith,

3 months ago I tested some Zeiss Standards on a Phantom HD, the wider ones did indeed porthole when wide open. By T4 they were fine.

Stephen

Good to know.

I wonder if there is some way they could modify the shape of the microlenses to reduce this effect.

If the chip was spun (like an LP record) and the lenses were heated to partially melt them again, in theory they should be distorted more towards the outer perimeter because their angular momentum would be greater there.

However I'm not sure whether that would make the problem better, or worse :rolleyes:

In theory, the rays coming in at an angle at the outer edges could be made to strike the lens surface more perpendicularly, but I'm not sure what would happen to them after that....

Stephen Williams · October 24, 2007

Hi Keith,

With my test I was specifically looking for the problem using a white background. Those lenses also have a problem with a P+S adapter. Moody scenes I am sure would work fine.

Stephen

Good to know.

I wonder if there is some way they could modify the shape of the microlenses to reduce this effect.

If the chip was spun (like an LP record) and the lenses were heated to partially melt them again, in theory they should be distorted more towards the outer perimeter because their angular momentum would be greater there.

However I'm not sure whether that would make the problem better, or worse :rolleyes:

In theory, the rays coming in at an angle at the outer edges could be made to strike the lens surface more perpendicularly, but I'm not sure what would happen to them after that....