2009 prime lenses

[Adrian Sierkowski]

I think Kubricks were just F0.7 I'm not sure, Sturrt and Karl, that they were T0.7, though that's not really all that important.

[K Borowski]

Well, to be fair, Kubrick had t0.7 primes then, but they were specially adapted by Nasa. It's not like they were readily available from any rental house.

 

Right, I know they were custom-made. But, at the same time, nearly four decades later, shouldn't we have even *faster* lenses? Seems like the opposite has taken place. Coatings had gotten better, but I think even this is at a stand-still now.

 

Howabout someone coming up with an iris diaphragm that doesn't reveal individual elements, more like the original Waterhouse (sp?) stop system.

[Stuart Brereton]

Right, I know they were custom-made. But, at the same time, nearly four decades later, shouldn't we have even *faster* lenses?

 

Kubrick's lenses, whether they were f0.7 or t0.7 were pretty close to the theoretical maximum aperture, so there's not much room for improvement there anyway. As to why there's not more of these lenses available, well, there's simply no demand. The current vogue for shallow DoF is comparatively recent, and even those DP's that like to shoot wide open at t2 or 1.4 probably have no desire to go wider. There comes a point when the difficulty in using such a lens (screwed up takes due to focus problems) outweigh the advantages.

[Stephen Williams]

Kubrick's lenses, whether they were f0.7 or t0.7 were pretty close to the theoretical maximum aperture, so there's not much room for improvement there anyway. As to why there's not more of these lenses available, well, there's simply no demand. The current vogue for shallow DoF is comparatively recent, and even those DP's that like to shoot wide open at t2 or 1.4 probably have no desire to go wider. There comes a point when the difficulty in using such a lens (screwed up takes due to focus problems) outweigh the advantages.

 

Hi Stuart,

 

I would much rather a lens that performed very well wide open @T2 than aT1.4 or T0.7 that needed to be stopped a couple of stops. I guess I am not alone

 

Stephen

[K Borowski]

Hi Stuart,

 

I would much rather a lens that performed very well wide open @T2 than aT1.4 or T0.7 that needed to be stopped a couple of stops. I guess I am not alone

 

Stephen

 

I agree.

[Arni Heimir]

From my figuring there are quite a few sets coming to the market. RED, IB/e, Jan's set, a new Zeiss set, and one more company that I can't remember the name (may actually be Jan's set.)

 

Pretty exciting time for new glass.

 

Matthew

 

I didn't know Zeiss had new lenses coming. Sounds exciting though. Any sources I could look at?

[K Borowski]

There comes a point when the difficulty in using such a lens (screwed up takes due to focus problems) outweigh the advantages.

 

I disagree.

 

I think misremembering lines, answering a call on a cell phone during a take, casually, unapologetically, or blaming the DOP for ruining your concentration during a take are equal disadvantages.

 

Adrian, please don't take this as hostility, but are you really going to argue an eighth of a stop? If you have a different T-stop, feel free to contribute it. . .

 

 

I'm not trying to pick fights with anyone here, or be a film geek, but I take real exception when salesmen try to con everyone into believing that a blatant rehousing of a lens-maker's glass is new glass, and not just an elaborate adapter.

 

I mean, at least do a good job. Christ I've taken apart "third-party lenses" for the purpose of cleaning off dust or to re-calibrate them to see Pentax, Nikon/Nikkor, Rodenstock, etc just blatantly encased in a shoddy plastic adapter ring.

 

Marketing and re-branding serve a valid purpose, but at least do a good job of it. Expect to be found out if you can't even take the original manufacturer's name off of the barrel.

Edited March 12, 2009 by Karl Borowski

[Stuart Brereton]

I would much rather a lens that performed very well wide open @T2 than aT1.4 or T0.7 that needed to be stopped a couple of stops.

 

Me too. t2 is wide enough, and even that can give focus pullers problems, particularly at night.

[K Borowski]

Me too. t2 is wide enough, and even that can give focus pullers problems, particularly at night.

 

There isn't a single lens that performs best wide-open made today. You're always best stopping down 2- to 2 1/2 stops for optimal sharpness, depending on lens.

 

So if you'd need a T-2 (t2 sounds like a certain Arnold Schwarzenegger movie) camera stop, the only way to get that would to have a lens with a maximum stop of T-1 or even faster!

 

This isn't a debatable subject, or a matter of opinion. The science of the matter dictates that slight stopping down minimizes the distortion you get from rays of light coming from the extreme edges of the lens, while not getting too much distortion due to fringing on the aperture blades.

 

But, at the same time, obviously very shallow or very heavy depth of field, used creatively, outweigh the technical limitations of shooting wide open or closed all the way down.

 

Obviously, T-0.7 will give pullers trouble. But, then again, anything over 2.8 gives me trouble personally. Sometimes it's part luck part lens being that in-tune with the lens.

 

Just a slight nitpick, not that it really matters, but when you talk about depth of field, isn't it always supposed to be referred to as F/stops, as T-stops only have to do with light transmission, not depth of field?

Edited March 12, 2009 by Karl Borowski

[Stuart Brereton]

There isn't a single lens that performs best wide-open made today.

 

Just a slight nitpick, not that it really matters, but when you talk about depth of field, isn't it always supposed to be referred to as F/stops, as T-stops only have to do with light transmission, not depth of field?

 

Master Primes and I believe, Cooke S4's are designed to perform equally well wide open as at deeper stops.

 

As far as F-stop vs T-stops go, I have never heard anyone refer to F-stops on set. I regard them as interchangeable, at least as far as DoF calculations go.

[Leo Anthony Vale]

You could always find a bar that offers free WiFi Web access, and get the best of both worlds :D

 

Or better yet, a bar next to a Scientology outlet and use the Scientologist's WiFi access.

 

Unfortunately, I don't have WiFi on my ancient, big and heavy laptop.

[K Borowski]

Master Primes and I believe, Cooke S4's are designed to perform equally well wide open as at deeper stops.

 

As far as F-stop vs T-stops go, I have never heard anyone refer to F-stops on set. I regard them as interchangeable, at least as far as DoF calculations go.

 

I HAVE heard of lenses designed to work "at their best wide open" but just like "95% fat free" this is misleading. I can say with 99.99% certainty that no lens that is tack-sharp wide-open won't be all the more tack sharp two stops down.

 

Whether F/- and T-stops are used casually on film sets is more in your realm of knowledge than mine, but T-stops are absolute, calibrated light transimission values taking in mind the degree of random scatter and dispersion due to lens optics (the more elements, the more potential there is for light loss as in a zoom). F/stops are a mathematical measurement of the ratio of the lens focal length iin comparison to the diameter of the diaphragm opening of the lens's aperture.

 

So, regardless of terminology, if you want to talk about DOF, ro do DOF calulations, you should be using the F/# you're at, not the T-#.

 

But again, this may be nitpicking. What's the biggest F/ to T- differential you've ever seen, a half a stop? Light meters are usually only reliable to within +/- 1/4 stop (and that's if you are using them right!)

[Stuart Brereton]

So, regardless of terminology, if you want to talk about DOF, ro do DOF calulations, you should be using the F/# you're at, not the T-#.

 

 

Lenses are compensated for the loss of light transmission from a theoretical F-stop to a T-stop by opening the iris slightly. As you point out in your post, DoF is a function of the "mathematical measurement of the ratio of the lens focal length in comparison to the diameter of the diaphragm opening of the lens's aperture"

 

As a t-stop is actually wider than an f-stop we should really be using t-stops to calculate DoF....

[K Borowski]

As a t-stop is actually wider than an f-stop we should really be using t-stops to calculate DoF....

 

IDK what you mean by "wider" but T-stops are always "slower" than F/stops. How you compensate from one to the other is really a matter of personal preference, but the size of the diaphragm and the focal-length of the lens are the only two things that matter for circle of confusion calculations. DOF is where you use F/stops and T-stops are what you use for adjusting the lens to what your light meter tells you.

[Matthew Rogers]

I didn't know Zeiss had new lenses coming. Sounds exciting though. Any sources I could look at?

For a while now on Reduser Mitch Gross who works at Abel Cine Tech in NYC said they were going to be showing a new set of primes at NAB. Someone the other day mentioned that Band Pro was going to be showing new lower cost Zeiss lenses and Mitch jumped on board saying that Band Pro would not be the only vendor showing these lenses. So until NAB, there's not much news except that they are Zeiss lenses. Not sure if Arri has their hand in them, or if someone else is just using the Zeiss glass.

 

Matthew

[Stuart Brereton]

IDK what you mean by "wider" but T-stops are always "slower" than F/stops. How you compensate from one to the other is really a matter of personal preference, but the size of the diaphragm and the focal-length of the lens are the only two things that matter for circle of confusion calculations. DOF is where you use F/stops and T-stops are what you use for adjusting the lens to what your light meter tells you.

 

Karl,

 

Lens manufacturers compensate for the loss of light transmission by marking the aperture ring in t-stops. The way they do this is by measuring the mathematical f-stop, then opening the iris by a measured amount and then marking that as a t-stop. Therefore t-stops are wider than f-stops, and have less DoF at any given focal length.

 

It may be that DoF tables are calculated from f-stops, but all that means is that they are ever so slightly wrong. That's fine though, because just about every focus puller realizes that they are slightly wrong and consequently doesn't stake their whole career on them... :-)

 

Circles of Confusion have nothing to do with lenses. They are dependent on your capture and display medium.

[John Sprung]

As a t-stop is actually wider than an f-stop we should really be using t-stops to calculate DoF....

 

No, use f/stops for DOF and T/stops for exposure. That's why some lenses have both f/ and T/ scales (and some cleverly use one scale with two witness marks).

 

f/stops are purely geometrical optics, and so is DOF. That's why they belong together.

 

If light loss in the glass is insignificant, then f = T. That's why simple little primes often have only an f/stop scale.

 

The T/stop is merely what the f/stop would be on a theoretically lossless lens that passes as much light as the real lens you're using. That's why T/stops are just for exposure. They're just f/stops with a light loss correction.

 

The T/stop is always deeper than or equal to the f/stop, like T/3.2 and f/2.8. So, using them for DOF can give you the illusion that you have more DOF than you really do.

 

 

 

 

-- J.S.

[Stephen Williams]

If you are that worried about DOF use the lens specific charts provided by Cooke & Zeiss. They take into account the thickness of the lens & the difference between T & F stops. With a little experience looking through an optical eyepiece will give you the information you need!

 

Stephen

[Dan Goulder]

If you are that worried about DOF use the lens specific charts provided by Cooke & Zeiss. They take into account the thickness of the lens & the difference between T & F stops. With a little experience looking through an optical eyepiece will give you the information you need!

 

Stephen

Do you find that the Cooke DOF charts are consistent enough to use for any spherical lens, or are there other factors which will vary the DOF depending on the lens? (I know that differences in lens construction will affect the minimum focus distance, and just wondered if such differences might also have any effect on DOF, or if those measurements are virtually identical for focal length/T-stop regardless of manufacturer.)

Thanks.

[Stephen Williams]

Do you find that the Cooke DOF charts are consistent enough to use for any spherical lens, or are there other factors which will vary the DOF depending on the lens? (I know that differences in lens construction will affect the minimum focus distance, and just wondered if such differences might also have any effect on DOF, or if those measurements are virtually identical for focal length/T-stop regardless of manufacturer.)

Thanks.

 

Hi,

 

They are close enough for other primes too, however for a big zoom I would use the correct tables.

 

Stephen

[John Sprung]

Theoretically, DOF is purely a geometrical calculation, which is why it can be computed and published in tables. The ASC manual has had voluminous DOF tables for many years.

 

When Zeiss and Cooke publish tables specific to their lenses, they compensate for whatever slight differences there are between their real lenses and theory. For instance, the actual focal lengths of real lenses aren't exactly the nominal focal lengths. What's marked as a 50 mm might actually measure as 52.11 mm or 48.23 mm. So, the generic ASC manual tables are a safer bet than using one that's specific to a different lens than the one you're actually using. And DOF doesn't suddenly fall off a cliff. It rolls off gradually, so this stuff is rarely all that critical and precise numbers really aren't so important.

 

BTW, f/stops for DOF, T/stops for exposure..... That's really the main thing to remember.

 

 

 

 

 

-- J.S.

[Stuart Brereton]

some lenses have both f/ and T/ scales (and some cleverly use one scale with two witness marks).

 

I own a very nice zoom marked in both f-stops and t-stops. Watching the iris as you change from f.5.6 to t 5.6, you can quite clearly see the aperture getting wider.

 

 

The T/stop is always deeper than or equal to the f/stop, like T/3.2 and f/2.8. So, using them for DOF can give you the illusion that you have more DOF than you really do.

 

This isn't true. It is actually the reverse. The t-stop is wider than the f-stop in order to compensate for the loss in transmission. Therefore T-stops have less DoF.

 

From the Cooke DoF Tables for 25mm lens Focus at 5' .

 

t2.8 3'10 1/2" - 7'1 1/3"

f2.8 3'9 1/4" - 7'5 1/4"

 

The difference is small, but the fact remains that although it is necessary to use f-stops for DoF calculations, the actual DoF resulting from your t-stop will be slightly less

[John Sprung]

I think the confusion here is the meaning of "using them for DOF".

 

Suppose we look at that lens that has both scales, and find that at indentically the same position of the iris blades, we get f/2.8 and T/3.5. Generic DOF tables are given in terms of f/stops, so looking up 2.8 will get you the right numbers. Looking up or computing with 3.5 will get you wrong numbers that indicate significantly more DOF than the correct version.

 

A DOF table given in terms of T/stops would only be valid for the specific make and model of lens for which it was calculated. Light loss isn't uniform, it tends to be worse at shallower stops. The all-purpose ASC type tables are only for f/stops.

 

 

 

 

 

-- J.S.

[Stuart Brereton]

I think the confusion here is the meaning of "using them for DOF".

 

Suppose we look at that lens that has both scales, and find that at indentically the same position of the iris blades, we get f/2.8 and T/3.5. Generic DOF tables are given in terms of f/stops, so looking up 2.8 will get you the right numbers. Looking up or computing with 3.5 will get you wrong numbers that indicate significantly more DOF than the correct version.

 

A DOF table given in terms of T/stops would only be valid for the specific make and model of lens for which it was calculated. The all-purpose ASC type tables are only for f/stops.

 

I'm sure we are just getting ourselves lost in definitions. My point is that if the diameter of the aperture at F2.8 is, for example 25mm, it will be fractionally bigger, say 27mm at T2.8. This larger aperture is to compensate for light loss, and as we all know larger apertures have less DoF.

 

Obviously, as every lens has a different degree of compensation, you can't use t-stops to calculate "all-purpose" DoF tables. Therefore you use F-stops, and that means that your DoF will be slightly misleading.

[John Sprung]

I think we're on the same page now.... ;-)

 

 

 

 

-- J.S.