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What S35 lens would yield these framings?


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#1 Karel Bata

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Posted 14 July 2011 - 12:12 PM

I'm not going to say what the original chip size was (yet) because some folks will just use a calculator! My suspicion is that the camera readout is innacurate because my calculations seem wrong to me, as would yours also be.

Please state whether you're going by personal judgement/experience, or are using some aid (in which case which?)

Many thanks for helping me out here. ;)

Posted Image
1 - distance: 4.8 metres


Posted Image
2 - distance: 3 metres


Posted Image
3 - distance: 2 metres


Posted Image
4 - distance: 1 metre


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#2 Stephen Williams

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Posted 14 July 2011 - 04:39 PM

Unless you were shooting on S35 or a S35 chip this is just a silly question, a 50mm lens is always a 50mm lens, which could be a wide angle, normal or tele lens depending on the format.

I'm not going to say what the original chip size was (yet) because some folks will just use a calculator! My suspicion is that the camera readout is innacurate because my calculations seem wrong to me, as would yours also be.

Please state whether you're going by personal judgement/experience, or are using some aid (in which case which?)

Many thanks for helping me out here. ;)

Posted Image
1 - distance: 4.8 metres


Posted Image
2 - distance: 3 metres


Posted Image
3 - distance: 2 metres


Posted Image
4 - distance: 1 metre


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#3 Karel Bata

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Posted 14 July 2011 - 05:51 PM

I puzzled over your answer, till I realised that - doh! - I'd put the question in the singular. I didn't mean which one single S3D lens would produce all four pictures in S35 format at those distances (and obviously one focal length could not do that) but instead which S3D focal lengths (get the plural there) would yield each of the different framings at those distances? in other words, what four lens settings would give those framings?

My bad for using the singular.

The reason I ask is because this is part of a series of tests to determine the spacial distortion of various combinations of lenses, distances, and inter-ocular settings when shooting 3D. Here you are only seeing the left eye. This was shot using a video camera where the lens readout seems to me to be wrong. Like, using various conversion tables and calculators the last is supposed to be the S35 equivalent of 28mm. At 1m? That don't look right to me. Anyone else got an opinion on this..?

Edited by Karel Bata, 14 July 2011 - 05:53 PM.

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#4 Stephen Williams

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Posted 15 July 2011 - 02:49 AM

The reason I ask is because this is part of a series of tests to determine the spacial distortion of various combinations of lenses, distances, and inter-ocular settings when shooting 3D. Here you are only seeing the left eye. This was shot using a video camera where the lens readout seems to me to be wrong. Like, using various conversion tables and calculators the last is supposed to be the S35 equivalent of 28mm. At 1m? That don't look right to me. Anyone else got an opinion on this..?


Forget about 'equivalant' focal lengths, the focal length is what is written on the lens. There is no equivalent for distortion.
The Equivalent nonsense normally refers to FF35 which is probably why your S35 conversion is wrong.
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#5 Karel Bata

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Posted 15 July 2011 - 03:40 AM

Sigh....

Stephen, your comment "There is no equivalent for distortion." shows that you don't appear to understand the nature of spatial distortions in 3D cinematography. Don't worry - few folks do. Yet you are content to be wholly dismissive of my query.

An image space distortion for an excessive IA might be represented like this:

Posted Image

That's for a Panny AG-3DA1 at 7ft (Panasonic recommend a minimum of 10ft to avoid this). Likewise the 1:30 'rule of thumb' is independent of lens focal length.

So it could be argued that when investigating this issue the actual focal length is neither here nor there. However when discussing this with cinematographers they always ask "What lens is that?" Answering that it's Xmm on a Y" chip is unsatisfactory, and the convention is to refer to 35mm focal lengths.

Edited by Karel Bata, 15 July 2011 - 03:41 AM.

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#6 Stephen Williams

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Posted 15 July 2011 - 06:45 AM

Sigh....



So it could be argued that when investigating this issue the actual focal length is neither here nor there. However when discussing this with cinematographers they always ask "What lens is that?" Answering that it's Xmm on a Y" chip is unsatisfactory, and the convention is to refer to 35mm focal lengths.


In theory yes, in practice no. 2 lenses of different manufacture will be different, even 2 lenses 1 serial no apart.

There is no convebtion to refer to 35mm focal lengths, this is made up by fools who have no idea what they are talking about.

If I shoot 16mm motion, 35mm motion, 35mm Anamorphic, 35mm stills or 6x6 cm, 6 x9 cm, I put the relevant lens on the camera I want I don't convert, but I have been shooting for 30 + years long before small chip photo cameras came on the market.
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#7 Karel Bata

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Posted 15 July 2011 - 07:48 AM

Strange. When I screened the video the other evening to a group of professionals, some of whom you would probably know, or at least have heard of (and some with a lot more experience than either you or I), there was some discussion about what the equivalent focal length should actually be. We all agreed the calculation I'd used was somehow flawed, but there was no suggestion that such a conversion was only ever done by fools.

I do see your point. But would a cinematographer used to 35mm working on a HDTV shoot for the first time and asking for the equivalent of 50mm lens really be regarded as a fool? It's a very common thing to do, to look up equivalents, and professionals are well aware of the limitations.

Edited by Karel Bata, 15 July 2011 - 07:50 AM.

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#8 Stephen Williams

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Posted 15 July 2011 - 08:42 AM

I do see your point. But would a cinematographer used to 35mm working on a HDTV shoot for the first time and asking for the equivalent of 50mm lens really be regarded as a fool?


If a DOP does not know what focal length to ask the assistant to put on the camera, he will be replaced very quickly. The AC will be laughing at you. Assuming he has shot S16mm he will have no problem with HDTV 2/3 focal lengths as they are close.

Your confusion is the equivalent lens relates to FF 35mm Still photography NOT S35 motion picture, so it's less help than you think. Bear in mind that other than in Newspaper & wildlife photography FF 35mm was an amateur format, pros shot 6 x 6 or bigger.

A 'standard' lens for S35 is approx 32mm, FF roughly 50mm S16 roughly 15mm 6x6 roughly 85mm.

FWIW the last shot with a 28mm lens S35 as about right for FOV 1.00m -1.10m range, however it's does not 'look like' a 28mm lens was used on a S35 camera. The first shot would equate to approx 120mm
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#9 Karel Bata

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Posted 15 July 2011 - 09:08 AM

Huh?

Why are you now talking about stills photography? You've somehow made the assumption these stills came off a DSLR? Why?

And here's some of those 'fools' you're talking about AbelCine and Panavision

But really, what is your problem? 'silly', 'nonsense', 'fools'? Have I offended you elsewhere...?

:wacko:

I reckon the framings above at those distances, in S3D land, and despite Stephen's intense disapproval, are somewhere around 200, 110, 70, and 40. Just judging by eye. Anyone care to comment?
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#10 Stephen Williams

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Posted 15 July 2011 - 09:22 AM

Normally Equivalent calculations are to FF35 so people 'knoe what there doing'

If you have an Iphone with Pcam you can do a simulation, what I said matches the simulation, it's roughly the same as my Nikon D300 so I think there right.

As you can see it would be much easier just to read off the aczual focal length of the camera at the time!

It's just easier & more professional if people just learnt what they were doing & did not convert to something else. Why is it of any importance what the lens would have been on another camera system that your not using? I just get bored of answering questions from people who have problems with doing conversions!

Huh?

Why are you now talking about stills photography? You've somehow made the assumption these stills came off a DSLR? Why?

And here's some of those 'fools' you're talking about AbelCine and Panavision

But really, what is your problem? 'silly', 'nonsense', 'fools'? Have I offended you elsewhere...?

:wacko:

I reckon the framings above at those distances, in S3D land, and despite Stephen's intense disapproval, are somewhere around 200, 110, 70, and 40. Just judging by eye. Anyone care to comment?


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#11 Dom Jaeger

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Posted 15 July 2011 - 10:21 AM

At the risk of getting bashed attempting to intervene in a fistfight..

In terms of field of view, any DOP worth the title should know which focal length suits a particular format. There are plenty of apps or online guides if they're unsure, eg http://www.abelcine.com/fov/

But as Stephen correctly pointed out, the distortion of a particular focal length will vary with different lenses. An 18mm Zeiss Super Speed may not yield exactly the same image as an 18mm Cooke S4, for example. Abberations such as barrelling, pin-cushioning or breathing will vary from brand to brand, especially at wide focal lengths or with anamorphics. Sometimes focal lengths are approximations. Zooms are even less predictable.

It's one of the difficulties of 3D work that without compensating software even 2 lenses that are the same brand, series and focal length may not perfectly match each other through their focal range.
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#12 Karel Bata

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Posted 15 July 2011 - 11:35 AM

Do you find pCam to be accurate?

Well, thanks for all the advice about lens aberrations, but it's something I'm very aware of - particularly when working in 3D. These lenses seem well matched though.

I had no idea about the specific focal lengths on that particular camera, which I've never seen before and probably never will again. Call me foolish, let ACs laugh at me, but I just asked for a distance and framing - the tests are about 3D space distortion. The actual focal length didn't matter. But of course people will later ask, so the camera assistant wrote down some numbers. I did some focal length conversions later, and to my 35mm sensibility they now look wrong to me. Well, wrong in the sense that a strict 'conversion' in this case won't work. So yes, the tables are clearly rubbish. But since I can't rely on everyone being familiar with a camera that has it's own individual framing quirks, no matter how unprofessional that might be of them, the easiest thing is to somehow figure out what the rough S35 equivalent would be had it been a S35 camera. You know, ball park.

It is NOT a test to do with lens distortion.

Edited by Karel Bata, 15 July 2011 - 11:36 AM.

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#13 Ben Syverson

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Posted 15 July 2011 - 12:00 PM

I think the reason most people get confused is that there's no consensus on what an "equivalent" lens would be. So first, you have to come up with a personal criterion. For me, the most important thing is horizontal FOV. Some people prefer diagonal FOV, because different formats have different aspect ratios. That has never made sense to me. Well, different strokes.

Once you know your criterion, the calculations are exceedingly simple. Just take your focal length and divide it by the relevant dimension of Sensor 1, to get a format-agnostic focal length multiplier. To find the equivalent on any format, multiply the constant by the relevant dimension of Sensor 2. You have to decide if you want to compare horizontal, vertical, diagonal, etc.

For example, if I like 28mm lenses on my full-frame Canon (36mm wide sensor), I would do: 28.0 / 36.0 = 0.7777. If I want the same exact HFOV on S35 (24mm wide sensor), I just do: 0.7777 * 24.0 = 18.6666. I could also find the equivalent for my 8x10 view camera (254mm wide sensor): 197.555, or about 200mm. If you always convert the same two formats, you can consolidate this process into a simpler "crop factor." For an HFOV conversion from S35 to 135, it's 1.5. Just multiply or divide by 1.5 to go back and forth.

People get confused and think "a 50mm is always a 50mm on every format." Well, that's true, but meaningless. FOV is what you're interested in comparing, and FOV for the same lens changes with the format.

Eyeballing your stills, I would roughly guess at this progression (all focal lengths assuming S35 format):
1. 75-90mm
2. 50mm
3. 30-35mm
4. 24mm

It would be handy if you could pick up a Canon DSLR with a cropped sensor (Rebel, 7D, etc). The horizontal dimension of its sensor roughly corresponds with the horizontal dimension of S35, so it could be useful for previewing focal lengths.
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#14 John Holland

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Posted 15 July 2011 - 12:05 PM

So Karel how many 3D films are you involved in at this time ?
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#15 Stephen Williams

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Posted 15 July 2011 - 01:10 PM

Pcam is spot on, if you know format size & focal length there is nothing to go wrong.

It^s the DOP's job to know the lenses for the camera he is using, how could he possibly direct the other units if he did not know what was going on.

I have been matching motion control to 3D for 25 years, it's never easy, takes time & patients to do well. Zoom lenses can be a nightmare & primes are rarely exactly the focal length written on them.

The no's people want & need are the real world no's not a conversion to something else by someone who may have never worked on S35 film.

Do you find pCam to be accurate?

Well, thanks for all the advice about lens aberrations, but it's something I'm very aware of - particularly when working in 3D. These lenses seem well matched though.

I had no idea about the specific focal lengths on that particular camera, which I've never seen before and probably never will again. Call me foolish, let ACs laugh at me, but I just asked for a distance and framing - the tests are about 3D space distortion. The actual focal length didn't matter. But of course people will later ask, so the cameraze assistant wrote down some numbers. I did some focal length conversions later, and to my 35mm sensibility they now look wrong to me. Well, wrong in the sense that a strict 'conversion' in this case won't work. So yes, the tables are clearly rubbish. But since I can't rely on everyone being familiar with a camera that has it's own individual framing quirks, no matter how unprofessional that might be of them, the easiest thing is to somehow figure out what the rough S35 equivalent would be had it been a S35 camera. You know, ball park.

It is NOT a test to do with lens distortion.


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#16 Stephen Williams

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Posted 15 July 2011 - 01:21 PM

Eyeballing your stills, I would roughly guess at this progression (all focal lengths assuming S35 format):
1. 75-90mm
2. 50mm
3. 30-35mm
4. 24mm

It would be handy if you could pick up a Canon DSLR with a cropped sensor (Rebel, 7D, etc). The horizontal dimension of its sensor roughly corresponds with the horizontal dimension of S35, so it could be useful for previewing focal lengths.


My money is on (if such lengths existed)

120
75
45
25


Of course they are very close for FF35 which is what I said earlier, I rest my case.

Huh?

Why are you now talking about stills photography? You've somehow made the assumption these stills came off a DSLR? Why?

And here's some of those 'fools' you're talking about AbelCine and Panavision

But really, what is your problem? 'silly', 'nonsense', 'fools'? Have I offended you elsewhere...?

:wacko:

I reckon the framings above at those distances, in S3D land, and despite Stephen's intense disapproval, are somewhere around 200, 110, 70, and 40. Just judging by eye. Anyone care to comment?


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#17 Karel Bata

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Posted 15 July 2011 - 01:49 PM

hmm.. Hhere's what my pCam shows me (format 35mm full aperture - 1.33):

Posted Image

Sorry it's soft, I took that with a phone. Here's that first image again:

Posted Image

about 174mm (I've assumed his head would be slightly bigger than hers)

and you guys say 75-90, and 120. That's a huge amount of difference!

So what the hell is it?

Edited by Karel Bata, 15 July 2011 - 01:53 PM.

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#18 Stephen Williams

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Posted 15 July 2011 - 01:57 PM

Wrong settings try 35mm Super 3 + 4 perf - 1.78 then it will all make sense. I have the advantage that I shoot 35mm film most weeks!

You might wast to look at 4k RED, the lenses will be even wider as the recorded area is smaller than S35.

I would also say that the face size does not match, your too zoomed in on the pcam.

hmm.. Hhere's what my pCam shows me (format 35mm full aperture - 1.33):

Posted Image

Sorry it's soft, I took that with a phone. Here's that first image again:

Posted Image

about 174mm (I've assumed his head would be slightly bigger than hers)

and you guys say 75-90, and 120. That's a huge amount of difference!

So what the hell is it?


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#19 Karel Bata

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Posted 15 July 2011 - 02:20 PM

I'd deliberately zoomed in on him a bit to compensate for his slightly bigger head size - she's only a kid.

35mm Super 3 + 4 perf - 1.78 seems to comes out at 160.

But you have thrown me there. If no area of the negative is allocated to the soundtrack, aren't those two settings the same width on the negative? So a given lens focal length should yield the same subject image size, but the 1.78 is cropped top and bottom? Do I need to go Google the Technicolor format charts..?
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#20 Stephen Williams

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Posted 15 July 2011 - 02:35 PM

I'd deliberately zoomed in on him a bit to compensate for his slightly bigger head size - she's only a kid.

35mm Super 3 + 4 perf - 1.78 seems to comes out at 160.

But you have thrown me there. If no area of the negative is allocated to the soundtrack, aren't those two settings the same width on the negative? So a given lens focal length should yield the same subject image size, but the 1.78 is cropped top and bottom? Do I need to go Google the Technicolor format charts..?


I still think it's nearer 120, 135 is too zoomed in, there is huge head room. I tried to match the head sizes exactly.

S35 does not have a sound track & can't be projected in a normal theatre as it's SUPER nor regular.
R35 would be 35mm Projevtion area 1.185 then there is room for a soundtrack need to zoom out a bit nearer 100mm IMHO.
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